My project is a Housing Authority remodel that has to meet Energy Star, thus be ASHRAE 55 compliant. Of course our budget is limited, but we are reusing perimiter HW finned tube in one of the buildings and adding Cooling only PTACs. The other building is EBB heat and adding PTACs as well. All apartments are one-bedroom and the PTAC will be placed in the living room with the intent that the adjacent bedroom is conditioned by the living room unit (remember budget constraints!). Fresh air is either windows or a central unit dumping into the corridors. My questions are as follows:
1.) Can I even do this with a PTAC and then if so can I do it with a single PTAC serving 2 rooms? It is definitely individual control, but multiple rooms, air speeds, humidity, etc are what they are based on the unit running per room temps.
2.) Am I reading correctly that radiant systems prevent me from using operative temps all together?
3.) If so, what programs are best recommended to figuring Mean Radiant Temps? (I do not believe my typical load program gives me this data)
Thanks
Christopher Schaffner
CEO & FounderThe Green Engineer
LEEDuser Expert
963 thumbs up
January 25, 2016 - 10:33 am
I think you have a more basic issue. If you are relying on the windows for ventilation, the GBCI reviewers will only grant this credit if you can show comfort and ventilation can be met at the same time (i.e. with the windows open).
Lindsay Austrom
Mechanical EngineerStantec
21 thumbs up
January 25, 2016 - 12:17 pm
David, I agree with Christopher's comment in terms of your first issue to address. However, it sounds like you may have a central ventilation system using corridor pressurization. In that case, I'll address your items 2 and 3.
2) If you have radiant heating/cooling, then you cannot assume that the operative temperature is equal to the space air temperature -- see ASHRAE 55 Appendix C. The operative temperature must then be calculated using the formula in Appendix C using the air temperature and mean radiant temperature (MRT).
You've described the heating as HW finned tube and EBB and the cooling as PTACs, which are all either free or forced convection. Do you have any radiant heating or cooling?
3) I use the ASHRAE Thermal Comfort Tool (purchase from ASHRAE, discount for members) which does include a MRT calculator. I don't know if any other software tools have the same. The CBE Thermal Comfort Tool requires manual input of either the operative temperature or air temperature and MRT.
You could also do a manual MRT calculation using the equations provided in Chapter 9 of the ASHRAE Fundamentals Handbook -- there is one for seated and one for standing occupants.