Covid-19 Antibody Seroprevalence in Santa Clara County, California - <AUTHOR> https://www.medrxiv.org/content/10.1101/2020.04.14.20062463v1 <comment><USER2> Caveat from the paper:

"This study had several limitations. First, our sampling strategy selected for members of Santa Clara County with access to Facebook and a car to attend drive-through testing sites. This resulted in an over-representation of white women between the ages of 19 and 64, and an under-representation of Hispanic and Asian populations, relative to our community. Those imbalances were partly addressed by weighting our sample population by zip code, race, and sex to match the county. We did not account for age imbalance in our sample, and could not ascertain representativeness of SARS-CoV-2 antibodies in homeless populations. Other biases, such as bias favoring individuals in good health capable of attending our testing sites, or bias favoring those with prior COVID-like illnesses seeking antibody confirmation are also possible. The overall effect of such biases is hard to ascertain."

<comment><USER3> Yes, and look at the way they corrected for this. They rebalanced for demographics, and that doubled their estimate. This is exactly the opposite of what they should have done. For example, zip codes farther from the testing sites were less likely to get tested, and more likely to be positive.

What you see is that certain groups were less likely to go get tested, UNLESS they had a good reason to think that they were positive. This should cause them to want to underweight the data from the underrepresented groups, but instead they overweighted it.

You can almost say that there were two populations that they were testing: White women who lived near a testing site who thought "what the hell, I'm bored with this quarantine so might as well get my finger pricked", and people who thought "I wonder if that thing I had a few weeks ago was COVID." The number you want is the prevalence from the bored white women. Bored white women might be somewhat skewed from other demographics, but probably not by that much. People who thought they might have had it is a massively skewed group. Effectively their correction removes the bored white women near a testing site, and only counts the people who have reason to think they had COVID.

<comment><USER4> With the average adult getting two bouts of common cold each year and mild COVID symptoms resembling a common cold, I'd think a large fraction of the population might think they had it. I wouldn't dear to guess in which way this shifts the estimate.

I think it's understood, that with such a small sample size, results are to be taken cautiously. You have to start somewhere though.

<comment><USER3> There was another serological survey of blood donors in Castiglione d'Adda in Italy. That one came up 70% positive. That town had 1.4% of its population die in March. That suggests an IFR of 2%, not counting people who were sick and might die from COVID in April.

<comment><USER5> We do need to be careful talking about "IFR" as with a disease with such high age-dependence demographic skews heavily alter population IFR.

Castiglione d'Adda has more people over 70 than Santa Clara County has over 65; population over 65 is about 60% higher relatively. Population under 18 conversely is about 22% lower.

Hard to do the math exactly, but if you simply switch 8.1% of your population from being children to being 80+, you raise IFR by 0.6% per the Imperial College China estimates. Combined with the hospital triaging Italy was doing, I don't think sub-1% IFRs in Santa Clara county are improbable. (though I do think this survey's claims are improbably low)

sources: [https://www.citypopulation.de/php/italy-localities- lombardia...](https://www.citypopulation.de/php/italy-localities- lombardia.php?cityid=09801410001)

[https://www.census.gov/quickfacts/santaclaracountycalifornia](https://www.census.gov/quickfacts/santaclaracountycalifornia)

[https://www.thelancet.com/journals/laninf/article/PIIS1473-3...](https://www.thelancet.com/journals/laninf/article/PIIS1473-3099\(20\)30243-7/fulltext)

<comment><USER3> I agree that you have to make an age adjustment for IFR, and your numbers seem reasonable. However, in the U.S. you also have a lot more diabetes, obesity, and high blood pressure, which are major risk factors. I wouldn't be surprised if that required a bigger adjustment than the age difference.

<comment><USER5> Agreed that US as a whole can have a high IFR.

Santa Clara county though is one of the healthiest places in the US. Life expectancy of 84 exceeds Italy in fact.

</comment></comment></comment></comment></comment></comment></comment><comment><USER6> There are similar high infection rates from other semi-randomized samples.

[https://www.nejm.org/doi/full/10.1056/NEJMc2009316](https://www.nejm.org/doi/full/10.1056/NEJMc2009316)

> Between March 22 and April 4, 2020, a total of 215 pregnant women delivered > infants at the New York–Presbyterian Allen Hospital and Columbia University > Irving Medical Center . All the women were screened on admission for > symptoms of Covid-19. Four women (1.9%) had fever or other symptoms of > Covid-19 on admission, and all 4 women tested positive for SARS-CoV-2 > (Figure 1). Of the 211 women without symptoms, all were afebrile on > admission. Nasopharyngeal swabs were obtained from 210 of the 211 women > (99.5%) who did not have symptoms of Covid-19; of these women, 29 (13.7%) > were positive for SARS-CoV-2. Thus, 29 of the 33 patients who were positive > for SARS-CoV-2 at admission (87.9%) had no symptoms of Covid-19 at > presentation.

<comment><USER5> NYC has 30x the per capita death rate of Santa Clara county.

Santa Clara county only being 15% as infected is not consistent.

<comment><USER7> Just a hypothesis, but if being more frequently exposed makes it more likely that the disease will be more severe, then this is plausible. There is some evidence that e.g. doctors/nurses were more likely to die compared to their age cohort, possibly because of higher viral load.

<comment><USER8> I've definitely seen the opposite stated, that doctors/nurses are not actually more likely to die. I forget if it was Italy or NYC, but the fatality rate for doctors & nurses had been something like 0.5%. They are much more likely to be infected than anyone else, and there has (rightly) been lots written about the doctors and nurses who have died, which gives people this perception.

</comment></comment></comment></comment><comment><USER9> "We recruited participants by placing targeted advertisements on Facebook aimed at residents of Santa Clara County..."

I wonder if these ads mentioned the purpose of the study, or if that information was only given out after initial contact (I don't know enough about IRB requirements here).

A concern is that this could cause a selection bias for people who suspected they had the virus. People may respond to such an ad out of curiosity ("I think I had the virus, so it would be good to know for sure") or obligation ("I'm pretty sure I had the virus, so I should help out with this study").

It wouldn't have to be a large selection bias, either. Of the 3,330 people they tested, they found only 50 who tested positive.

I would like to see a bit of a better method of sample selection before drawing any conclusions.

<comment><USER10> Yes, the ads accurately described the study. Several friends of mine participated (I live in Santa Clara County).

Of course there is selection bias, which is why they make adjustments to make the sample better represent the population (see the abstract for details on this, or read the paper for all the details, there's well-established science behind these adjustments and it's up to the reviewers to be sure that they did it correctly). The point is that "they only found 50" is quite a large number compared to the number of confirmed cases.

<comment><USER9> What adjustments were made to account for selection bias of the sort described? It's not covered in the paper, and "well-established science" certainly doesn't answer the question.

<comment> compiler-guy These are very common statistical methods when dealing with surveys and populations. It isn't this paper's job to describe the background on something like that, just like it isn't this papers job to explain blood testing.

They describe their limitations and adjustments exactly like most other studies of this sort do. For example:

"Those imbalances were partly addressed by weighting our sample population by zip code, race, and sex to match the county. "

<comment><USER9> On the contrary - detecting selection bias of this sort can be very difficult. Do you measure it using a questionnaire? You might ask your subjects "Do you think you previously had COVID-19?" But what do you do with that response data? Exclude everyone that says yes? Then you're skewing one way. There's obviously no population data to match that response with like there is for general demographics such as race and age.

Many studies are only as good as their sampling methods. A good sampling method will alleviate concerns of selection bias.

<comment><USER11> I think you'd call individuals(using a method with far less self selection bias) and get them to fill out the same questionnaire and then do the same types of adjustments you'd do with race or gender.

But I also agree they 100% did not do any of these adjustments if they did it would be listed right here

> We report the prevalence of antibodies to SARS-CoV-2 in a sample of 3,330 > people, adjusting for zip code, sex, and race/ethnicity. We also adjust for > test performance characteristics using 3 different estimates: (i) the test > manufacturer's data, (ii) a sample of 37 positive and 30 negative controls > tested at Stanford, and (iii) a combination of both.

</comment></comment></comment></comment></comment></comment><comment><USER12> It's hacky and I'm happy to be told how wrong it is. But based on these recent antibody studies in Germany, Finland, and now here in CA, I've been assuming an actual fatality rate of about 0.4, and thus an actual infected rate of 250x our known deaths, which is a much firmer number.

This is only a small comfort since it means we _may_ have had about 8.75 million infected and presumably now immune in the USA. Or about 2.6%. There's still a long way to go in that case.

<comment><USER13> I've been using 0.5% for mental math, rounding down from the lower bound from this study in The Lancet:

[https://www.thelancet.com/journals/laninf/article/PIIS1473-3...](https://www.thelancet.com/journals/laninf/article/PIIS1473-3099\(20\)30243-7/fulltext)

I would be surprised if, after this current wave of infections, the percentage of people with antibodies in the US is higher than the low single digits.

Herd immunity without a vaccine is a pipe dream. Our best bet is to massively ramp up testing and contact tracing and really start pushing the number of infections down to a point where parts of society can start functioning again.

<comment><USER14> Herd immunity isn't a pipe dream it is just one hell of a sacrifice. And we'd better check the immunity actually lasts before we try that. Frankly I've never been a great fan of the 'flatten the curve' explanation, sure the graphs seem nice but I reckon the peak in those graphs is drawn too low by several orders of magnitude.

In the Netherlands a fatality rate of 0.5% would mean it'd take about a year for herd immunity to kick in assuming we managed sustain the peak that occurred about 2 weeks ago (and it's somewhat dubious whether the healthcare system actually _can_ sustain that peak).

<comment><USER15> One aspect that people seem to be ignoring with the whole 'healthcare capacity' argument is the mental health of the healthcare workers. The capacity everyone talks about is IMO the acute capacity, not really the chronic sustained capacity.

That's because just like in a war, it isn't realistic to expect the frontline soldiers to stay in combat for longer than weeks at a time before they start to exhibit PTSD and their effectiveness begins to drop.

Unless we have large reserves of doctors and nurses to rotate in and out I think we should be very careful not to take them for granted.

</comment></comment></comment></comment><comment><USER16> I made this comment the last time a serological testing study came out: they have 30 negative controls and claim 1.5% positives among their tests. So the number of controls is insufficient to rule out this being entirely false positives. You have to then rely on the test manufacturer's claims of false positives rates, which comes from 371 negative controls. They say:

> our estimates of specificity are 99.5% (95 CI 98.1-99.9%) and 100% (95 CI > 90.5-100%)

Look at the those confidence intervals, even the narrower one (from the manufacturer's data)! The bottom is a four-fold increase in false positives, compared to the point-estimate, and is greater than the total positives they had in their finding.

<comment><USER17> To repeat you in plainer English: the serum test isn't infallible and reports "infected", incorrectly, for uninfected patients. It does this at some rate that is very near, or perhaps larger than, the fraction of "true" infected patients they report in their results.

Teasing out data from all that noise requires that the false positive error rate be measured very accurately. And they didn't do that, so really this doesn't tell us much.

Edit: Alternatively, borrowing jargon from a more common field around here: the measured infection rate of ~3% is very close to the noise floor of the experiment. It might be that, or it might be near zero, and we can't tell the difference. This study is very good evidence that the infection fraction is not much larger, however. We can easily rule out high infection rates like the 30% numbers that seems to get thrown around.

</comment></comment><comment><USER18> I don't see anything in the methods about potential crossreactivity with NL63, OC43, or HKU1 coronaviruses. _Presumably_ this was done by the company, but crossreactivity is an extremely important control when it comes to this type of test. It is common, and if it's not vetted thoroughly, you may be measuring something else completely.

</comment><comment><USER19> Add this to growing pile of evidence that this coronavirus is more widespread than most testing to date would suggest. How much more widespread still appears very unclear. There is a major ramping up of antibody testing happening right now, and multiple new tests being introduced, so we should have a better idea very soon.

But the takeaway should be that this is a good thing. Every unknown case we uncover decreases the overall rate of hospitalization and death, and potentially decreases the effective transmission rate (assuming most people who had the virus develop immunity and that the immunity lasts, which is also still unclear).

<comment><USER20> I don't follow your argument. If the epidemic is more widespread than initially thought, why do you assume that the effective transmission rate would potentially decrease? If anything, the transmission rate was higher than assumed and, due to the higher number of infections and how they spread exponentially,it would only ramp up.

And additionally, there are reports of reinfections among covid19 patients who were found to be cured.

<comment><USER21> _" If the epidemic is more widespread than initially thought, why do you assume that the effective transmission rate would potentially decrease?"_

Herd immunity. If testing is only detecting 1/50th of cases in NYC, for example, it means that there have been about 6M cases, or about 69% of NYC's population. That's basically the threshold where we'd expect to see the infection counts level off naturally.

<comment><USER22> there is no herd immunity if reinfection can occur, which appears to be the case

<comment><USER21> There is no credible scientific evidence that reinfection can occur. There have been, at most, anecdotal reports from unreliable sources.

<comment><USER23> And there are good reasons to believe reinfection shouldn't be possible, to be clear - it's not just being dismissed out of hand.

</comment></comment></comment></comment></comment></comment><comment><USER24> The problem with every one of these studies I've seen is that they come up with around 3% of the population having antibodies, while a typical false- positive rate for these tests is also around 3%. In this case they claim they adjust for the specificity (basically false-positive rate), but I didn't see that they reported what the specificity was.

If the mortality really is very low, then it should be easy to prove. Just go to NYC, do some random testing, and show us an infection rate that far exceeds the false-positive rate.

<comment><USER25> This is certainly not a study. And certainly shouldn't be taken as good data of any kind, but it is interesting: [https://www.livescience.com/coronavirus- in-pregnant-woman-hi...](https://www.livescience.com/coronavirus-in-pregnant- woman-high-nyc.html)

Sure as hell isn't random (all pregnant women... so all women for one. All at the same hospital is another).

"Between March 22 and April 4, those hospitals screened 215 pregnant women for SARS-CoV-2 (the virus that causes COVID-19), and 33 women, or 15%, tested positive. Of these who tested positive, 29 women — or nearly 14% — showed no symptoms."

<comment><USER26> Anyone know if there's been a follow-up to see if the women eventually developed symptoms?

</comment></comment></comment><comment><USER27> I don't see anything about sampling bias here. I would assume that people who have been ill, experienced mild symptoms, or who were exposed to confirmed cases would be more likely to respond to the facebook ads recruiting testing volunteers.

I'm sure we are significantly undercounting cases but I highly doubt we are off by a magnitude of 50x.

<comment><USER28> I know. 50-85x is hard to believe. How could we be _that_ far off?

<comment><USER5> It's impossible to believe. Currently, Santa Clara's crude CFR is 3.7%.

NYC has similar demographics (and as bad nursing home hits?) -- 0.14% of the population has died from covid. That puts an upper bound of 26x (and that's if the entire population was infected)

<comment><USER29> You have no reason to believe that the Santa Clara CFR is correct, and dividing the CFR of one city by the IFR of another is meaningless.

</comment></comment></comment></comment><comment><USER30> With only 30 people in the negative control group, the confidence interval on the false positive rate would easily swamp out the results of the study for 1.5% positive sample ratio, no?

Seems kind of useless unless your control group is a lot larger, and the false positive rate can be shown to be <<1.5%.

</comment><comment><USER31> "Participants were recruited using Facebook ads targeting a representative sample of the county by demographic and geographic characteristics."

How is it representative when it's only Facebook users in this sample?

<comment><USER5> Unless you think FB users for some reason would be infected at significantly different rates, that shouldn't be much of a problem.

I'm much more concerned about selection bias toward prior sick people; IIRC, Stanford offered to report positive results to the patient.

<comment><USER32> There would potentially be an age bias, though probably less in FB than a lot of other services you could cherrypick from. It'd also arguably bias older, since FB has been aging up in audience from what I can tell.

Without reading the study, though, possible they actually controlled that in the demographic profile for the ad.

Edit:

Going to the other thread confirmed this. From the paper,

"This study had several limitations. First, our sampling strategy selected for members of Santa Clara County with access to Facebook and a car to attend drive-through testing sites. This resulted in an over-representation of white women between the ages of 19 and 64, and an under-representation of Hispanic and Asian populations, relative to our community. Those imbalances were partly addressed by weighting our sample population by zip code, race, and sex to match the county. We did not account for age imbalance in our sample, and could not ascertain representativeness of SARS-CoV-2 antibodies in homeless populations. Other biases, such as bias favoring individuals in good health capable of attending our testing sites, or bias favoring those with prior COVID-like illnesses seeking antibody confirmation are also possible. The overall effect of such biases is hard to ascertain."

</comment></comment></comment><comment><USER33> There's also some data coming out of Wuhan around antibody testing. The methodology is not as well formed as the study in the OP but there is still value in the data.

> Wuhan's Zhongnan Hospital found that 2.4% of its employees and 2% to 3% of > recent patients and other visitors, including people tested before returning > to work, had developed antibodies, according to senior doctors there.

Additional antibody testing is also underway in Wuhan.

Source: [https://www.wsj.com/articles/wuhan-starts-testing-to- determi...](https://www.wsj.com/articles/wuhan-starts-testing-to-determine- level-of-immunity-from-coronavirus-11587039175)

<comment><USER5> It is far more credible that Wuhan hit 3% infection rate (that's about double the PCR testing rate of the evacuees) than Santa Clara county, with an order of magnitude lower death count, having a 2% rate.

</comment></comment><comment><USER34> I think the numbers will coma out to show this ripped through the USA in February; we slammed the barn doors closed well after the horse was gone.

Of course that's not the narrative that fits agendas so just like with "why cant we test people?" back then, there will be many official reasons not to look for antibody data and to doubt what data gets gathered.

<comment><USER35> Based on the difference between CA and NY, I'd be willing to bet that it got here earlier, maybe in December.

<comment><USER36> You would have seen more reports in hospitals of interstitial pneumonia, as well as a higher YoY death rate during January.

<comment><USER37> The CDC is reporting an abnormally high pneumonia death rate in January, and it can't be explained by confirmed flu cases:

[https://www.cdc.gov/flu/weekly/#S6](https://www.cdc.gov/flu/weekly/#S6)

Look carefully at the black and red graph after the phrase "mortality surveillance data".

<comment><USER36> The graph and text clearly state it refers to pneumonia and influenza, if you refer to the legend where it says Percent P&I. The P&I for the first 8 weeks of the year is clearly within normal ranges. It spikes from baseline in the first week of March continuing on to the present day.

If you look at the first set of graphs, you'll see a spike around the same time for influenza tests. I don't know how fast pneumonia occurs in people weakened by influenza, but I would expect some delay.

I think the spike in both influenza and in death due to influenza and pneumonia is probably due to testing. If you presented with influenza like symptoms in March, you were definitely given a flu test to rule out influenza.

</comment></comment></comment></comment></comment><comment><USER38> my friend probably had the virus (2 inconclusive tests) and tried to get into this study. some group asked her for $125 to get tested. i'm not sure if she saw any of the facebook ads. so, grain of salt about representativeness of the sample. there's for sure a response bias towards people who think they had it.

<comment><USER39> Just curious, did your friend have pretty severe symptoms? As in, was it worse perceivably than say a case of bad flu?

</comment></comment><comment><USER40> There could be a meaningful distinction between exposure and infection. I would define the first as anyone who was exposed to the virus (or even just parts of the virus) and generated antibodies. The second would be an actual infection and presumably a sufficient antibody response to repel the virus and confer immunity to another infection. Really you can generate antibodies without even getting exposed to live virus, just like you can develop allergy to pollen or other foreign objects that enter your body. I would say only the second case is meaningful for public health. For that you need to look at how people do convalescent plasma. You need to test for specific antibodies that actually confer immunity.

</comment><comment><USER41> There are now multiple sources of evidence pointing to a very low true infection fatality rate, as low as 0.1% in some regions. Iceland has been testing a semi-random sample using PCR since early in the epidemic, and there have been several small antibody surveys in "hot spots" showing infection rates over 15%. You can also use CDC surveillance of flu-like illnesses to estimate the total number of infected nationwide; this morning I posted an analysis of this data estimating only 1 in 40 cases were detected in March, consistent with the Stanford results: [https://fivetran.com/blog/covid-19-count](https://fivetran.com/blog/covid-19-count)

<comment><USER42> It may have a low overall fatality rate, yet it seems to have a high rate of hospitalization in clinical cases.

<comment><USER43> > it seems to have a high rate of hospitalization in clinical cases.

The raw hospitalization rate is inflated because both treatment and testing are mostly limited to very severe cases in places where there's a lot of confirmed cases (e.g. NYC.)

<comment><USER42> Still, comparing it to influenza... we dont see this many severe cases typically.

<comment><USER43> Its pretty obvious this is worse than the flu. I don't think anyone is really disputing that at this point.

</comment></comment></comment></comment></comment><comment><USER44> Saw this comment [1] on Reddit that outlines the limitations of the study well:

This is the most poorly-designed serosurvey we've seen yet, frankly. It advertised on Facebook asking for people who wanted antibody testing. This has an enormous potential effect on the sample - I'm so much more likely to take the time to get tested if I think it will benefit me, and It's most likely to benefit me if I'm more likely to have had COVID. An opt-in design with a low response rate has huge potential to bias results.

Sample bias (in the other direction) is the reason that the NIH has not yet released serosurvey results from Washington:

We're cautious because blood donors are not a representative sample. They are asymptomatic, afebrile people [without a fever]. We have a "healthy donor effect." The donor-based incidence data could lag behind population incidence by a month or 2 because of this bias.

Presumably, they rightly fear that, with such a high level of uncertainty, bias could lead to bad policy and would negatively impact public health. I'm certain that these data are informing policy decisions at the national level, but they haven't released them out of an abundance of caution. Those conducting this study would have done well to adopt that same caution.

If you read closely on the validation of the test, the study did barely any independent validation to determine specificity/sensitivity - only 30! pre- covid samples tested independently of the manufacturer. Given the performance of other commercial tests and the dependence of specificity on cross- reactivity + antibody prevalence in the population, this strikes me as extremely irresponsible.

This paper elides the fact that other rigorous serosurveys are neither consistent with this level of underascertainment nor the IFR this paper proposes. Many of you are familiar with the Gangelt study, which I have criticized. Nevertheless, it is an order of magnitude more trustworthy than this paper (both insofar as it sampled a larger slice of the population and had a much much higher response rate). It also inferred a much higher fatality rate of 0.37%. IFR will, of course, vary from population to population, and so will ascertainment rate. Nevertheless, the range proposed here strains credibility, considering the study's flaws. 0.13% of NYC's population has already died, and the paths of other countries suggest a slow decline in daily deaths, not a quick one. Considering that herd immunity predicts transmission to stop at 50-70% prevalence, this is baldly inconsistent with this study's findings.

For all of the above reasons, I hope people making personal and public health decisions wait for rigorous results from the NIH and other organizations and understand that skepticism of this result is warranted. I also hope that the media reports responsibly on this study and its limitations and speaks with other experts before doing so.

[1] [https://www.reddit.com/r/COVID19/comments/g32wjh/covid19_ant...](https://www.reddit.com/r/COVID19/comments/g32wjh/covid19_antibody_seroprevalence_in_santa_clara/fnotu78/)

<comment><USER45> It's better to have data and know its limitations, than not to have data at all.

<comment><USER46> This may be a true statement when applied to public health professionals, but is quite likely dangerous to public welfare when in the hands of disinformation campaigns and propaganda.

</comment></comment></comment><comment><USER47> "These prevalence estimates represent a range between 48,000 and 81,000 people infected in Santa Clara County by early April, 50-85-fold more than the number of confirmed cases. Conclusions The population prevalence of SARS-CoV-2 antibodies in Santa Clara County implies that the infection is much more widespread than indicated by the number of confirmed cases."

</comment><comment><USER48> This thread critiques this article in a way I find convincing: [https://twitter.com/DiseaseEcology/status/125122527387113472...](https://twitter.com/DiseaseEcology/status/1251225273871134721)

</comment><comment><USER49> Great to see actual testing on a representative population sample, though I'm not sure what the consequences ought to be:

> These prevalence estimates represent a range between 48,000 and 81,000 > people infected in Santa Clara County by early April, 50-85-fold more than > the number of confirmed cases.

<comment><USER50> So with 69 deaths so far and 9 deaths last week in Santa Clara County, projecting that to an extra 4 weeks to 105 deaths for those infected in early April, that means a 0.16% death rate?

<comment><USER51> Lots of reasons I don't think you can extrapolate meaningful death rates from this yet. One big one is that time from infection to death covers a very wide range: in Wuhan time from hospitalization to death had both a mean and a standard deviation of about 2 weeks, and time from infection to hospitalization isn't well known yet, but is likely at least a week. Add to that the fact that some cases are diagnosed post-mortem and you might not know about all of the fatalities for early April cases until well into May.

</comment></comment></comment><comment><USER52> In our small town, I know of 3 people who came into direct contact with the first confirmed case, exhibited symptoms, but were refused testing. I can definitely believe their guess that the number of cases is an order of magnitude greater than the number confirmed.

</comment><comment><USER53> That is certainly alarming that it is so much more widespread than expected - it really highlights the failure of our controls against the virus and the importance of early testing. It I'd good news that this implies the death rate is less severe.

However, a caveat is that antibody tests might have high rates of false positives, which would be a particularly large problem when very few people are actually positive. So read this with a grain of salt. The paper isn't peer reviewed yet etc.

<comment><USER54> Most signs so far suggest that the virus is basically uncontainable, short of everyone on the planet taking aggressive measures to stop it escaping China back in January or December.

<comment><USER40> How do you square that with the fact that there is no outbreak in any overseas Chinese community? Not Taiwan or Hongkong or Macau, nor in the epicenter of Italy ([https://www.reuters.com/article/us-health-coronavirus- italy-...](https://www.reuters.com/article/us-health-coronavirus-italy- chinese/from-zero-to-hero-italys-chinese-help-beat-coronavirus- idUSKBN21I3I8)), nor San Francisco Chinatown ([https://www.nytimes.com/2020/04/17/us/san-francisco- coronavi...](https://www.nytimes.com/2020/04/17/us/san-francisco-coronavirus- chinese-hospital.html))? All of these communities have far more ties to mainland China.

<comment><USER55> It could have already passed through all of those communities basically unnoticed, and/or confused with other ILIs. There's no way to rule out that possibility, and when you consider how rare cardiovascular diseases (the most common comorbidity) are in those communities, you have to conclude that it's not vanishingly unlikely: [https://minorityhealth.hhs.gov/omh/browse.aspx?lvl=4&lvlid=4...](https://minorityhealth.hhs.gov/omh/browse.aspx?lvl=4&lvlid=49)

Obviously mitigation efforts still play some part in limiting the spread, but I would not bet that all of those communities were able to suppress such a contagious disease before a big chunk of the population was exposed to it.

<comment><USER40> Maybe Chinese emigrants in Italy are young so they didn't notice the wave. But Taiwan/Hongkong/Macau? They are testing and tracing. When their recent travelers to Europe and America came back, a lot of them were infected and caused a spike in cases. [https://www.nytimes.com/interactive/2020/04/09/world/asia/co...](https://www.nytimes.com/interactive/2020/04/09/world/asia/coronavirus- hong-kong-singapore-taiwan.html)

</comment></comment></comment></comment></comment><comment><USER56> I suspected the asymptomatic rate to be high, but not by a factor of 50-85! That's very great news no?

</comment><comment><USER57> This is very strong evidence that the "realists" like Alex Berensen were correct. The shutdowns probably should end, while encouraging at-risk populations (mostly retired) to stay at home.

<comment><USER46> Data from Wuhan was that in the early phase of the epidemic about 70% of infections were transmitted at home. Once they realized this, they went to rapid isolation of positive tests and quarantine of contacts in "COVID hotels" away from home.

So your suggestion is entirely unworkable unless there is a plan to remove all at-risk persons from contact with low-risk persons.

Please show your work and let us know what that plan looks like. Who will care for these people, how will they be housed, how will you prevent the care force from bringing infection to them ala nursing homes, etc.

<comment><USER57> Guess what? We have been doing it your way for 45 days. Everyone infected is now locked in a house with others. They too are now infected. Intrafamilial and nosocomial infection is much more powerful than community -- that has been proven here and in earlier epidemics.

And yet anti-science morons in SF clutch their scarf over their mouths when you jog past them.

</comment></comment></comment><comment><USER58> Antibody tests are not as accurate as RT-PCR, but the sensitivity that was observed here was 91% and 99% specificity when compared to confirmed COVID cases. I just want to point out that these researchers are using the corrects tests to do this.

<comment><USER59> They use the correct tests, but they use them on a group that isn't even close to a random sample of the population, which is what you'd need to do to get to their conclusion.

<comment><USER58> I'm not going to comment on that because I have a basic understanding of public health and epidemiology on the diagnostic side of things. Why do you think that this isn't a "good" random sample?

<comment><USER60> It's not a random sample; it's a convenience sample of people who responded to Facebook ads.

<comment><USER58> What about Facebook ads doesn't mean that they're an adequate sample? Is there a confounding factor that you have in mind?

<comment><USER60> Many confounding factors. Socioeconomic factors that can't be fixed with stratified sampling (access to transportation, usage of Facebook, etc.. conversely the willingness of a $10 amazon gift card to motivate people to participate will vary). People who are concerned about possible past exposure to COVID-19 may have a different probability to respond.

Of course, the bigger issue is that we can't rule out that the antibody tests have a false positive rate that can explain the whole result. We need serology tests in places with a higher positive rate to know.

Basically, 50 positive results out of 3330 is a really small signal. Just a small false positive rate or sampling issue could explain all the positive results.</comment></comment></comment></comment></comment></comment>


Show HN: Halite – A simple libsodium wrapper for PHP projects - <AUTHOR> https://github.com/paragonie/halite <comment><USER2> Just wanted to give OP, CiPHPerCoder, a shoutout.

His work is all really high quality and he works very hard. Halite is great for the PHP crypto crowd (if you are unfortunate enough to be in that crowd...it is small). Really high quality project.

</comment><comment><AUTHOR> Hi HN,

I've been working on this project for a year now, and looking to push for a version 3 release before 2016 is over.

Halite takes a lot of guesswork out of cryptography. You don't even need to know what a nonce is to use it successfully.

I'd like to get more feedback from other developers if possible.

<comment><USER3> Looks nice on the surface. The only thing that leaps out at me from the readme, is the lack of a suggested way to store/recover the salt? Ideally I'd see a function that takes a "password" and some "plaintext" \- generates a salt from an OS provided source, an IV (if applicable) and returns a package of the cipher-text along with the salt (and IV).

I suppose there might be instances where the cipher-text without the salt might be useful -- but I can't immediately think of any. Keeping the salt "semi-secret" is akin to using a two-key system: the password the user knows, and the salt that the server knows -- but it strikes me as a brittle way of doing things, and provides unclear promises wrt. availability etc (can the user always recover the data, only remembering the password?).

One could of course _construct_ such a function on top of the primitives provided here - but I think it would make a lot of sense to provide something along the lines of:

      * sym_enc(password, plaintext) >
         -> returns "box" autogenerated-salt|ciphertext
         -> possibly with a version header, indicating
            KDF (&enc algo) used (could just be a magic
            number)
        Should obviously use an AEAD mode

     * syn_dec(password, box)
        -> retrieves key by getting KDF, salt from
           box, regenerating key
        -> and returns decrypted plaintext

There's nothing wrong with exposing the KDF-functions I suppose, but it feels like it's aiming a bit low, in close proximity to ones feet.

<comment><AUTHOR> > The only thing that leaps out at me from the readme, is the lack of a > suggested way to store/recover the salt? Ideally I'd see a function that > takes a "password" and some "plaintext" \- generates a salt from an OS > provided source, an IV (if applicable) and returns a package of the cipher- > text along with the salt (and IV).

Generally you want to just do this once:

        $key = KeyFactory::generateEncryptionKey();
        KeyFactory::save($key, '/path/outside/webroot');

And from then on:

        $key = KeyFactory::loadEncryptionKey('/path/outside/webroot');

Encryption typically never touches a password (although you can derive one from a password and salt if you so choose). The normal way of doing things is to just use a random key.

(My takeaway is: the README for v3 probably needs work to make this more clear.)

Thanks for the feedback! :)

<comment><USER3> Right. Still, after your last edit, the last section (the example with a password derived key) -- still stands out from the rest of the otherwise excellent readme -- in that it's not actually a usable example. I mean the code (appears to) _work_ \- but it's not an actually usable example like the others. Because it leaves a lot of questions up in the air (or worse, for an untrained eye, it might lead to implementing "one-way" encryption, if real data is encrypted, and the salt thrown away...).

</comment></comment></comment></comment><comment><USER4> [https://wiki.php.net/rfc/libsodium](https://wiki.php.net/rfc/libsodium)

</comment><comment><USER5> There's also a BitTorrent client by the same name, if anyone thought this sounded familiar.

</comment><comment><USER6> This looks really great, but I have to ask: why only support for PHP 7+? Is there any plan to support PHP 5.x? With only PHP 7+ it's more or less unusable in the large majority of current PHP projects or in common PHP hosting environments.

<comment><AUTHOR> We actually have a blog post for this exact question.

[https://paragonie.com/blog/2016/04/go-php-7-our- commitment-m...](https://paragonie.com/blog/2016/04/go-php-7-our-commitment- maintaining-our-open-source-projects)

The short of it:

* PHP 7 allowed us a combination of type safety and brevity that makes it much easier to reason about the security of Halite in a way that PHP 5 does not.

* There is a very bad habit in the PHP community, led by WordPress, to provide _very legacy_ support (i.e. PHP 5.2.4 in 2016). For that reason, we're going against the grain focusing on PHP 7 only. If people want to use any of our new open source libraries, they need to make the decision to upgrade now.</comment></comment>


Improve YouTube Video Playback by Disabling VP9 Support in Chrome or Firefox - <AUTHOR> http://www.cnx-software.com/2016/06/29/improve-youtube-video-playback-on-low-power-intel-mini-pcs-by-disabling-vp9-support-in-chrome-or-firefox/ <comment><USER2> As an addendum to this, I found out Chrome doesn't even have GPU acceleration enabled by default.

Type chrome://gpu in the address bar. If you've got of unavailable options there. Chances are it's off.

Type chrome://flags in the address bar. Click Enable on the first option under Experiments "Override software rendering list"

Saved me quite a few CPU cycles, voila.

<comment><USER3> It's enabled for most people. There might be a good reason why your GPU (or GPU drivers) are blacklisted; see [https://chromium.googlesource.com/chromium/deps/gpu/software...](https://chromium.googlesource.com/chromium/deps/gpu/software_rendering_list/+/cdf5c6133df8cc29f2b705f4025fb752ebe94cde/software_rendering_list.json)

<comment><USER2> Weird. Not anything I can see immediately. However this is an ATI 6970 I EFI flashed to work on a 2008 MacPro.

<comment><USER4> Really? The fact that you hacked a GPU to work on your Mac didn't immediately raise red flags?

<comment><USER5> There's absolutely no reason to suspect that a web browser cares what kind of firmware you used to boot your OS.

</comment></comment></comment></comment></comment><comment><USER6> I've been using h264ify in Chrome on OSX for some time, but lately it started having problems with seeking/rewinding. Have to switch to Safari when I want to rewind. Managed to cobble together a chrome extension that opens the current url in Safari, also pausing the video and using the current playback time (too rough to share).

</comment><comment><USER7> If you have mpv and youtube-dl, you can just `mpv [http://youtube.com/whatever`](http://youtube.com/whatever`) and it'll play. Much better performance than anything in browser from my experience.

I just have a keybinding for `mpv $(xsel -o)` which plays whatever url I have in my clipboard in mpv.</comment>


Mini Tablet Display Technology Shoot-Out - <AUTHOR> http://www.displaymate.com/Tablet_ShootOut_4.htm

<comment><USER2> I can't stand the 16:10 screen format which is terrible for everything except watching movies. That's the main reason our Nexus 7 is rarely used (and our kids are completely confused by the Android UX; although they're having a much harder time with iOS 7 than iOS 6, too).

<comment><USER3> I bought and prefer the Nexus 7 to the iPad Mini simply because it fits in my jacket and coat pockets. I've had and enjoyed iPhones and iPads in the past, so this was not a step I took lightly.

The most used application on any of my hand-held devices is the Kindle.app. I quite like reading on the Nexus 7 in portrait orientation. It doesn't feel too skinny.

<comment><USER4> My iPad Mini fits in my jackets' pockets, barely, but it does.

<comment><USER5> Of all my jackets/coats, only one has a pocket larger enough for an iPad Mini. That's where the Nexus 7 beats out the iPad.

<comment><USER3> All this talk about fitting in pockets reminds me of Jeff Hawkins, the inventor of the Pilot, who was said to carry a block of wood in his shirt pocket while developing the device.

I know the "pocket test" is one of the reasons why the original iPod was better than the Rio Nomad and other 1st gen hard drive based MP3 players.

</comment></comment></comment></comment></comment><comment><USER6> Dr. Raymond M. Soneira badly needs an Editor. His use of Winnie-The-Pooh Punctuation makes his Article far too hard to Read.

<comment><USER7> I'm not sure why the over use of capitals makes it hard to read, it seems very trivial to me to parse the over abundance of proper nouns. I suspect it was written this way to help NNP detection, possibly the author uses a service like AlchemyAPI and unknown runs of init-capitalized text causes NN to be parsed as NNP.

</comment></comment><comment><USER8> The Air's screen is outstanding in this regard. Usually you can trust Apple to not cut corners with this sort of stuff, so this is unfortunate. It's also strange because the larger screen uses IGZO tech as well.

<comment><USER9> Is it really that unfortunate? I've never noticed any color issues on my iPad 2.

I don't use it for any color-intensive content creation, but in several years of use it never even occurred to me that there might be a problem with its color accuracy.

<comment><USER10> At some point screens have to hit the 'good enough for most people' point just as processors did.

Apple has apparently concluded that the 'good enough' point is x2... if that's true, it makes sense that they're not building devices above retina density if there is little quantifiable benefit to 99.9% of end-users. Atleast until the tech becomes much cheaper.

<comment><USER11> It's really lucky for Apple that the "good enough" point happened to _exactly_ coincide with double their old pixel densities (plural, since they had two different densities on the iPad and iPhone), almost unbelievably so in fact.

<comment><USER12> That's... uh pretty disingenuous as an argument. The "good enough" point didn't have to be exactly the current densities, it just had to be less than the current densities... If the "good enough" point wasn't achieved with a doubling of the pixel resolution, Apple would still have doubled the pixel resolution, because exactly doubling brings a whole load of advantages from a technical or graphical design point of view. It's just that a few years later there would be another doubling until "good enough" had been surpassed.

<comment><USER13> As long as Apple decides it's good enough...then it must be good enough. ;P

</comment></comment></comment></comment></comment></comment><comment><USER14> I wonder if Apple went this way because of the supply chain more than anything. All indications are that Apple will be moving 2-3x more iPad minis than these competitors. I'm curious if they went with the safer IGZO panel because those other technologies just don't ramp up as well.

<comment><USER15> I find it curious and funny that it's always Apple that gets such benefits of doubt. When they have the best hardware, it's because they're years ahead of everyone else in their supply chain strategies. When they have the worst, it's because they must be hobbled by the same supply chain.

Would you have expressed the same comment for Google/Amazon if the Nexus or Kindle had the worst screen?

<comment><USER16> I wouldn't have - because they won't be selling anywhere near as many. What do you do if you have a choice to sell a few of a great product, or heaps of a slightly inferior one? I know which I'd choose, but Apple took the money and ran. I don't know what the figures will be, but I'd bet an order of magnitude more iPads are sold. Can the manufacturers of the better screen produce that many? I'm guessing no, but someone out there knows the answer.

<comment><USER15> So you're saying Apple's decision to put an older generation screen on the iPad Mini is justifiable because they still manage to sell many more than competitors who have gone out of their way to put in better hardware into their own products?

And you're saying this as an Apple customer?

<comment><USER17> Yes. People don't purchase the iPad alone, but for the ecosystem. I moved to Android but just bought an iPad as it has an App I need for work that isnt available on any Tablet OS. Thats why theyre able to do it and still win over the others.

</comment></comment></comment></comment></comment><comment><USER18> I find it interesting that this is the only tablet that hits the 300dpi threshold, and the next Kindle White is supposed to meet this as well. 300dpi is of course the resolution of most print magazines. The implication is obvious, but what isn't is why Apple declined to participate in this race.

<comment><USER19> Print magazines are actually closer to 600 dpi for black text while only 200 dpi or less for color (due to Moiré patterns and CMYK printing).

In any case, Apple have indicated that they're more interested in limiting screen resolution fragmentation than chasing a specific resolution number (both iPads have the same number of pixels and that number is exactly 2 times the original iPad).

<comment><USER20> Right, it's diminishing returns. My Retina iPad 4 looks great. Maybe an extra 100 dpi would make it look better, but it would require more hardware, redesigned programs, etc. Frankly I'm not sure I'd even be able to notice it.

Of course, if you're not using the standard RGB style screen, it may make a difference. Having an extra 100 DPI on a pentile screen may be noticeable. I don't know.

<comment><USER21> > Of course, if you're not using the standard RGB style screen, it may make a > difference. Having an extra 100 DPI on a pentile screen may be noticeable. I > don't know.

Pentile screens are only on certain Samsung AMOLED screens. No LCD on the market is using Pentile, so it's a moot point.

</comment></comment></comment></comment><comment><USER22> It looks better tho

<comment><USER7> "it" being? my co-reference parser raised an exception

<comment><USER23> Was the title of this article changed? There seem to be a bunch of comments as if the iPad Mini were singled out somehow in the title, but now it's just a generic tablet shootout.

This is why the HN policy of editing titles is really frustrating. People start discussing it based on the original title, and none of the discussion makes sense after it's been edited. I don't see why they don't simply implement a technical requirement that the title is the title of the page or some heading element on the page; that's what it ends up being edited to anyhow, just changing the title out from under everyone just leads to more confusion.

<comment><USER11> The "discussion" the other headline generated appears to be two really poor comments. I'd suggest this is an argument for the HN title policy.

</comment></comment></comment></comment><comment><USER24> It's too bad those other tablets are rubbish.

<comment><USER25> Nexus 7 is actually pretty good. Some reviews:

[http://www.anandtech.com/show/7231/the- nexus-7-2013-review](http://www.anandtech.com/show/7231/the- nexus-7-2013-review)

[http://arstechnica.com/gadgets/2013/07/the-2013-nexus-7-revi...](http://arstechnica.com/gadgets/2013/07/the-2013-nexus-7-review- meet-the-new-standard-for-android-tablets/)

<comment><USER26> I haven't been impressed with mine unfortunately. Issues:

1 - the display doesn't get dim enough; it's too bright to read in bed next to a partner

1a - this is _INCREDIBLY_ annoying: at the lowest brightness, the display flickers. Noticeably.

1b - I repeat 1a

2 - slow charging times

3 - it's not quite wide enough to read technical pdfs comfortably. Also, the software available to read pdfs generally is not particularly good. Ebookdroid is the best of a bad bunch. On the bright side, it can invert colors for reading in bed. However, it still isn't particularly good at finding the content in pdfs formatted for other screens, boxing it to exclude eg page numbers or headers, then filling the screen with just content.

Anyway, I found the slightly wider screen on an ipad mini better for reading pdfs. ymmv; if I where just reading kindle books and not reading in bed I'd probably like it better. Also, I'm over 6 feet tall and have big hands, so I find the mini comfortable. Again, ymmv.</comment></comment></comment>


Heat Pumps Work Miracles - <AUTHOR> https://dothemath.ucsd.edu/2012/06/heat-pumps-work-miracles/ <comment><USER4> I build controls for many heatpumps ([https://flair.co/pages/mini-splits-and- window-units](https://flair.co/pages/mini-splits-and-window-units)) and follow the space pretty closely. They are truly magical with respect to pumping heat from the cold outdoors into a warm indoor space.

That said, the efficiency gains on the energy consumption side are admirable. From a global warming standpoint however, heat pumps are actually still pretty bad because of the refrigerants.([https://www.drawdown.org/solutions/materials/refrigerant- man...](https://www.drawdown.org/solutions/materials/refrigerant-management)) This is not an issue with more traditional electric heaters (resistive or otherwise).

The real calculus for those concerned with global warming (I understand this was not the topic of the writeup) is the net effect of these systems over their lifetime - aka, Energy Saved and its GHG effect via leveraging a heat pump vs the GHG effect from the release of the refrigerant. Perhaps the real win would be a refrigerant recovery business that is...air tight :)

<comment><USER5> There is a such thing as a solid state heat pump which operates without refrigerants or any moving parts. They are not as efficient as regular heat pumps, though, at least currently. But maybe that could change.

[https://www.researchgate.net/publication/270646164_Efficienc...](https://www.researchgate.net/publication/270646164_Efficiency_of_a_thermoelectric_heat_pump)

[https://www.energy.gov/eere/buildings/downloads/high- efficie...](https://www.energy.gov/eere/buildings/downloads/high-efficiency- solid-state-heat-pump-module)

[https://arpa-e.energy.gov/?q=slick-sheet-project/high- effici...](https://arpa-e.energy.gov/?q=slick-sheet-project/high-efficiency- solid-state-cooling-technologies)

<comment><USER6> You reminded me of Lonnie Johnson's _" Johnson Thermo-Electrochemical Convertor"_, or JTEC for short. On their webpage they say they are aiming for 85% Carnot efficiency for converting heat to electricity, and it can run in reverse to become a heat pump[0][1].

Sadly, I can find no third-party measurements of how well it performs in practice, so I guess it's still in the R&D phase. I did find a nice talk by Johnson about the project though[2].

[0] [http://www.johnsonems.com/about/](http://www.johnsonems.com/about/)

[1] [http://www.johnsonems.com/benefits/](http://www.johnsonems.com/benefits/)

[2] [https://www.youtube.com/watch?v=F6FUk2E9-68](https://www.youtube.com/watch?v=F6FUk2E9-68)

</comment></comment></comment><comment><USER7> Modern heat pumps are truly a marvel, especially when you get one designed for heating and not just an AC-unit running in reverse. They're very common in Sweden and can easily warm an entire house even at -20 C.

Whenever this topic appears on HN I want to get on my soapbox and yell "INSULATION PEOPLE, INSULATION!". Most houses I've seen outside of the Nordics have shit-all insulation and that's depsite it working both ways - house stays cooler in the summer. It's such a small cost to add during construction and it pays off in a year or two, tops.

Modern, newly built houses in Sweden, way above the arctic circle, require less than 5000 kWh per year to heat and generate hotwater.

<comment><USER8> > It's such a small cost to add during construction and it pays off in a year > or two, tops.

Classic market failure: operational costs don't factor into home buying decisions prominently, so whatever small added construction cost is borne by the homebuilders (the cost of added insulation doesn't quite result in an equal increase of selling price).

Short of instituting a carbon tax that would make operational costs of heating suddenly more prominent and priced accordingly, this is a great case for efficiency standards in homebuilding. Suppose your home came with an "energy star" HVAC rating...

<comment><USER9> You can actually get your home Energy Star certified.

[https://www.energystar.gov/newhomes](https://www.energystar.gov/newhomes)

Some states have even offered tax credits for doing so.

<comment><USER8> Thanks for the link, didn't know about that!

</comment></comment></comment></comment><comment><USER10> It's worth noting that the temperatures at which heat pumps function well is more of a design choice than a fundamental limitation. You can make a heat pump which functions down to -20C with HFC refrigerants, maybe lower with some other types. However, you may choose to optimize 'mild weather' performance by forgoing low temperature performance. Modern heat pumps work pretty darn well across a range of temperatures.

What we really need are heat pumps which do not use HFC refrigerants - <USER2> are a pretty significant cause of global warming, and there are other options (CO2 being one of the best, in my opinion). [https://www.drawdown.org/solutions/materials/refrigerant- man...](https://www.drawdown.org/solutions/materials/refrigerant-management)

</comment><comment><USER11> Heat pump water heaters have efficiency of 3x+ vs .9 or so for gas or electric resistance. If you have have an electric resistance water heater get a heat pump model. It costs more upfront but will pay for itself in not too many years, especially considering many places have incentives. In the US natural gas is so cheap the economics are not nearly as good, it takes a long time to pay back the difference but does eventually. With even a modest carbon price obviously this would be different.

If you are going to replace your furnace or AC get a quote for replacing with a heat pump instead, either central or multiple mini-split heads. Heat pumps have gotten a lot better in recent years, particularly being able to work in cold weather down to 0F or below, expanding northward the places they are practical.

<comment><USER12> I can tell you that my heat pump set up at my condo is absolute trash here in Northern Ohio. Running 24/7 it is unable to get my condo above 62 deg F. It blows cold-ish air under an outside temperature of 40 deg F. Windows are new, doors are weather stripped. I'm having it run it in supplemental mode just to get it above 65 deg F.

<comment><USER13> My HVAC is utter crap ≠ HVACs are crap. This is a great example of a worthless anecdotal comment that distracts from the point. Give us some more detail like model number or install date? Is it a modern unit not coming close to its advertise performance? Is it appropriately sized for your condo?

</comment></comment></comment><comment><USER14> Big issue in the Netherlands (and probably more countries) will be noise pollution though. Houses here are built really close to each other and the combined noise could be an issue. Neighbours are already complaining about the noise from my parents heat pump.

<comment><USER15> Do you have any centralized district heating in NL similar to in Sweden?

<comment><USER14> In some newly developed areas we do, but most of the heating in the Netherlands runs on natural gas, since we have so much of it.

<comment><USER16> ...or rather _since we had so much of it_. The Dutch government is, after all, making noises about the country going 'off the gas' to become 'gas-free' around 2050. As to whether this really will happen and what it actually will entail - are they going to tell industry to stop using gas as well? - <USER3> to be seen but heat pumps are being pushed as one of the alternatives to gas. Given that nearly all central heating in the Netherlands is water-borne and most systems are designed for a high working temperature - between 70 and 90 degrees - the switch to a heat pump will need more than just a simple swap of the prime heater. Low-temperature (possibly fan-assisted) convectors can be used to replace high-temperature radiators, these can also be used to cool down the house in summer. More insulation is needed in most Dutch houses, even newly built houses sometimes don't have more than 10 cm of foam insulation in the roof and less in the walls.

</comment></comment></comment></comment><comment><USER17> The most recent season of This Old House, Jamestown Net-Zero House[0], is worth a watch for folks interested in learning more about home efficiency techniques in general.

[0] [https://www.thisoldhouse.com/watch/jamestown-net-zero- house](https://www.thisoldhouse.com/watch/jamestown-net-zero-house)

<comment><USER18> I'll add that to my must watch list - I live in an old (1930's) home that leaks heat like crazy, so I'm interested in possible retrofits, though I'm a bit concerned that it'll be a monstrous task.

<comment><USER19> Pretty much anything in a pre-1980 house will a nightmare to retrofit. Houses in the 1945 to 1965 era (in the US) especially were mostly built as quickly and as cheaply as possible.

The concept of energy efficiency didn't really exist before the 1973 oil crisis as oil use per capita was steadily going up and up until then.

Energy Star, for example, was only established in 1992.

Energy efficiency is very very recent.

<comment><USER18> Oh yeah, my home was built strictly to keep the frozen death out, I have to throw a big furnace at it to be livable while it exhausts everything through its impossible to insulate roof.

</comment></comment></comment></comment><comment><USER20> I had a "geothermal" heat pump put in to my house via Google's Dandelion and it works great so far. It's been -30F at my house but the ground sourcing renders that moot. As far as I can tell their innovation was going vertical so they didn't need to dredge up a huge loop of land. The pump has two channels that go down 300ft each and the fluid runs down and back up each bore hole.

It provides heat (working great so far), hot water (but I already had an electric inline heater, so I can't speak to the slow-refill issues), and A/C in the summer. I'm curious to see how well the AC performs!

<comment><USER21> I don't see Google mentioned anywhere on their site. What's the relation?

[https://dandelionenergy.com/](https://dandelionenergy.com/)

<comment><USER20> Alphabet spinoff, looks like: [https://dandelionenergy.com/about/](https://dandelionenergy.com/about/)

</comment></comment></comment><comment><USER22> Maybe I'm missing something, but no matter how efficient a heat pump is, doesn't it have a limit on how much heat it can pump as ∆T increases?

Even here in western NY we occasionally have to deal with -10 F (-23 C) weather for a week and so that's a pretty big temperature delta if you want a comfortable 68 F (20 C).

Combine that with the fact that gas is still quite a bit cheaper per unit of energy than electricity (in my area) and a heat pump just doesn't make any sense.

The ability to have a single unit heat and cool is definitely nice, but without a geothermal-like ambient temperature to work with, I just don't see this working out, even with all the insulation in the world.

<comment><USER11> Elsewhere in this thread fastbeef says "They're very common in Sweden and can easily warm an entire house even at -20 C [-4F]." So, it can work though at -10F you would probably need supplemental heat.

Of course in Sweden residential natural gas prices are almost 4 times what they are in the US so its a very different economic decision. Shows what a carbon tax can do.

[https://www.statista.com/statistics/702735/household- natural...](https://www.statista.com/statistics/702735/household-natural-gas- prices-in-selected-countries/)

<comment><USER7> Keep in mind that 1 kW worth of gas gives out 0.9 kW, while 1 kW of electricity entered into a heat pump gives out AT LEAST 3 kW of heat.

Also, no one uses gas for heating in Sweden. Very old houses down town use it for cooking only.

</comment></comment></comment><comment><USER23> Question to other engineers here. We were designing a "smart wine chiller" recently. Ran into a problem - small size sealed compressors are very, very, hard to come by, and if you want one that is also quiet, prepare your arm and a leg.

We ended up having the compressor custom made by local fridge factory. Engineers there told us that designing such a small piston compressor and hoping it to be reliable and efficient is a futile effort, but they still did their best.

Is between piston driven compressors, and peltier coolers, is there just anything on the market? More quiet and robust than small piston compressors, and more efficient than peltier?

<comment><USER24> Have you looked into compressors for mobile applications, such as a Danfoss 35F? I mean, technically its a reciprocating piston compressor, but the smaller ones can be quite quiet.

[https://assets.danfoss.com/documents/DOC223886433214/DOC2238...](https://assets.danfoss.com/documents/DOC223886433214/DOC223886433214.pdf)

<comment><USER23> Not small enough. The one we custom ordered is like 6x6cm (piston itself is only 9mm,) and they even managed to make it run on DC.

The factory and their tech level truly surprised me despite them being complete nonames, who mostly do fridge part kits for local production in 3rd world countries.

This reminded me yet another time of just how underappreciated are those no- name factories. They truly are the real unsung heroes of our globalisation era.

<comment><USER23> Adding to that, the most expensive single part in all at happened to be the specialty BASF o-ring for the piston at $6 dollars...

Body, piping, insulation, every other part came at less than that

</comment></comment></comment></comment><comment><USER25> Slightly OT, but..

I live in a temperate climate. I've sometimes wondered if it would be worthwhile to adjust house construction so that:

\- In the summer, the kitchen refrigerator's heating coils touch outdoors air instead of indoors air.

\- In the winter, the refrigerator's cooling is provided, at least partially, by the outside air.

\- In the summer (only), the kitchen oven vents into the outdoors rather than into the kitchen.

\- In the winter (only), a heat exchanger recovers some of the heat from our electric clothes dryer.

<comment><USER26> One idea i've had is to just make a central heatpump system.

Why does a fridge need its own compressor that vents heat back to the house even in the summer?

Why can't your water heater use that same heat instead?

This all started because my brother used to redirect dryer air back into his apartment during the winter, using a saw dust sock to keep the lint contained.

I started thinking about how heat could be better managed if everything used a central ac/heat pump. heat generated by the fridge, your computer, the ac, etc could be used by your water heater, your heater heater, your dryer.

Add heat recovery systems to your dryer, and your drains, and bam super sustainability.

<comment><USER27> There are AC units that do this: pipe the heat to the hot water tank first.

* [https://www.rheem.com/innovations/innovation_residential/int...](https://www.rheem.com/innovations/innovation_residential/integrated_systems/)

* [https://techcrunch.com/2011/06/12/air-conditioning-water-hea...](https://techcrunch.com/2011/06/12/air-conditioning-water-heater/)

Once the water tank reaches its max temperature, then heat is dumped outside.

The practical problem is that you need to have the different parts work together, and fridge makers don't don't to hot water makers.

<comment><USER26> >The practical problem is that you need to have the different parts work together, and fridge makers don't don't to hot water makers.

You don't need a fridge or a hot water heater or an ac or a furnace at that point, because the primary function has been offloaded to the central heat pump. you need heat exchanger attached to water, heat exchangers attached to a cold room, heat exchangers attached to a central air system.

You don't have to have the parts work together if the most expensive part of each appliance has been centralized. At that point you've now reduced the appliance to where to put the heat exchanger.

</comment></comment></comment></comment><comment><USER28> The most commonly used heat pumps utilize the external air as a source. Which is quite silly on a sunny but chilly day. Even 2m^2 black & isolated panel exposed to the sun will be tens of degrees warmer. Just putting the heat exchanger in some micro glass house with a valve would increase the efficiency.

</comment><comment><USER29> We have a heat pump and I love it, but for the longest time it was beyond me how the thing works. When it finally clicked, it blew my mind. The idea that there's heat to be found, even on a cold day, is amazing. It's actually what made me want to understand thermodynamics more deeply.

</comment><comment><USER30> Also heat pumps work a miracle because the fluids they use are NOT perfect, platonic fluids that obey the ideal gas law.

[https://en.m.wikipedia.org/wiki/Joule–Thomson_effect](https://en.m.wikipedia.org/wiki/Joule–Thomson_effect)

</comment><comment><USER31> This was a really lucid and engaging piece on the mathematics of these systems. I wish more math teachings would be done in long form like this instead of the cargo culted textbooks that are put out by major publishers.

</comment><comment><USER32> Talking about fridge, do you guys know if there's a use for heat collector out of the fridge radiator ?

Right now it's mostly wasted heat, or IIUC even worse, in closed spaces it forces more energy consumption from the fridge.

<comment><USER33> It's not a lot of heat in residential use cases.

Fridges for enclosed spaces should have a fan to push the air around.

The more space you give a radiating fridge, the more efficient it'll be.

I do wonder if a small fan on a radiating fridge would pay for itself if controlled by temperature probes.

</comment></comment><comment><USER34> BTW the whole blog is a goldmine. Rim-filled of evidence of how our energy- hungry civilisation can't last :)

</comment><comment><USER35> Heat pumps based on air do not work economically below 40F. Neighbor has one and his electric bill is out of control in the winter. Drop below freezing and the system will pump heat out of the house to de-ice the external unit, and electric resistance heat will kick in.

We have dual fuel, so we burn oil below 40F. Works great.

If you can afford it, putting in a heat pump that works off of ground will eventually pay for itself.

<comment><USER36> Outside temperature definitely affects an air heat-pump's performance, but the ones common in sweden stop being effective at -10c or even -15c.

I have a ground-source pump and its brilliant. But plenty of my neighbours are happy enough with air-source pumps.

<comment><USER37> Recent conversations with net-zero builders indicate that ground-source pumps are being pushed away for most single-family residential projects in favor of the new-generation, highly-effective, cold-climate air-source heat pumps.

Mitsubishi and Fujitsu seem to have a large lead in cold-climate air-source heat pumps that are rated effective to -13F (anecdotal reports greenbuildingadvisor.com indicating effectiveness down to -20F). Yet, talking to builders, contractors, friends, and family, you will often still hear old tales about how "heat pumps aren't effective below 40F". Heat pumps come in a wide range of flavors. It's clearly possible to heat your house exclusively using an air-source heat pump in most USA climates.

<comment><USER7> There's a huge difference between air-source heat pumps and rebranded AC units running in reverse. We have a Mitsubishi FH35 6kw heat pump that easily heats 80 m2 (800 sq feet) down to -13 C this winter.

<comment><USER15> Do you recommend the model you quoted in your comment?

<comment><USER7> I do, it's fantastic! Just make sure to get a good installer for it.

<comment><USER38> As a fellow northern climate person, now in Arizona, have you any idea its efficacy in the 45 celsius normal summer heat, for cooling?</comment></comment></comment></comment></comment></comment></comment>