What are the environmental conditions for SARS-CoV-2 to survive?
Because "any" Coronavirus is so dangerous, much research have been done on viruses with similar properties. They are called "surrogates". Because nCoV is new, we don't have any studies, so we need to estimate it's behavior from previously studied similar viruses.

Here:

RH   = Relative Humidity. 
Tr   = Room Temperature
TGEV = Transmissible Gastroenteritis (surrogate)
MHV  = Mouse Hepatitis (surrogate)


Viral survival for the TGEV/MHV surrogate:


on stainless steel:      4°C @ 20% RH:  28 days
in water/sewage (TGEV):  25°C: 22 days
in water/sewage (MHV):   25°C: 17 days
contaminated water is a potential vehicle for exposure if aerosols are generated


For airborne Human Coronavirus 229E (HCV/229E):


Optimal survival:  6°C @ 50% RH: 
Poor* survival:     20°C @ "High" relative humidity (RH)
(* "poor" in terms of 20°C but varying RH.)


For SARS CoV-P9:


Serum: 96 h = 4 days
Sputum &amp; Feces: 96 h = 4 days
Urine: 72 h = 3 days


For SARS-CoV (GVU6109):


in diarrheal stool (at low pH): 4 days
in respiratory/air droplets:  >7  days @ 20°C (Tr)
in respiratory/air droplets:  >20 days @ 4°C



  "The main route of transmission of SARS CoV infection is presumed to be respiratory droplets. However the virus is also detectable in other body fluids and excreta. The stability of the virus at different temperatures and relative humidity on smooth surfaces were studied. The dried virus on smooth surfaces retained its viability for over 5 days at temperatures of 22–25°C and relative humidity of 40–50%, that is, typical air-conditioned environments. However, virus viability was rapidly lost (>3 log10) at higher temperatures and higher relative humidity (e.g., 38°C, and relative humidity of >95%)."
  
  "We and others have reported that infectivity of SARS CoV (SARS coronavirus) was lost after heating at 56°C for 15 minutes but that it was stable for at least 2 days following drying on plastic."




UPDATE: 2020-03-13

From [7]: 


  "We found that viable virus could be detected in aerosols up to 3 hours 
  post aerosolization, up to 4 hours on copper, up to 24 hours on 
  cardboard and up to 2-3 days on plastic and stainless steel. HCoV-19 and 
  SARS-CoV-1 exhibited similar half-lives in aerosols, with median 
  estimates around 2.7 hours. Both viruses show relatively long viability 
  on stainless steel and polypropylene compared to copper or cardboard: 
  the median half-life estimate for HCoV-19 is around 13 hours on steel 
  and around 16 hours on polypropylene. Our results indicate that aerosol 
  and fomite transmission of HCoV-19 is plausible, as the virus can remain 
  viable in aerosols for multiple hours and on surfaces up to days."


For SARS-CoV-2:
Experiments were performed @ 40% RH and 21-23°C.


Copper (Cu):      4 hours
Stainless (Fe):   48 hours (2 days)
Cardboard:        24 hours 
Plastic:          72 hours (3 days)
SARS-CoV-2 is most stable on plastic and stainless steel.


References:


[1] 20xx https://aem.asm.org/content/76/9/2712.short
[2] 1985 https://www.microbiologyresearch.org/content/journal/jgv/10.1099/0022-1317-66-12-2743
[3] 2005 https://academic.oup.com/cid/article/41/7/e67/310340
[4] 2009 https://www.sciencedirect.com/science/article/abs/pii/S0043135409000785
[5] 2010 https://www.hindawi.com/journals/av/2011/734690/
[6] 2003 https://www.ncbi.nlm.nih.gov/pubmed/14631830  
[7] 2020 Aerosol and surface stability of HCoV-19 (SARS-CoV-2) compared to SARS-CoV-1