[TRNSYS-users] Garage Heating

[Fred Porter <fporter@archenergy.com>]

All;
I simulated an existing 5-bay garage and attached 2000 sf offices in 
Colorado, and calibrated a DOE-2 model with real weather and bills. 
Infiltration must be about 65% of the annual building heat load, even 
with fairly bad walls. The owner wants to build another one with minor 
changes. The garage is heated with overhead low-intensity tube heaters 
with a combined output of 200 Btuh/sf. The high capacity can also handle 
some ventilation, if anyone ever turned it on. When it is cold and the 
doors are opened the thermostats will kick all these heaters on. With 
bay doors on each side, the room is probably over 100 ac/hr for an hour 
per day and there are a few more hours with just one door open, 
depending on occupant behavior.

I notice that radiant hydronic in-floor heat is installed in repair 
garages at 35 Btuh/sf at design conditions, much lower than my system. 
It would seem the heat rate off the floor could increase momentarily 
when a draft of cold air hits a warm floor, but is limited over time to 
the much smaller boiler capacity. So is some of the claimed savings from 
in-floor heat in these types of spaces just from less "recovery 
capacity," and less output during periods of extreme airflow.  I suppose 
I could "simulate" this by merely reducing the capacity while leaving 
the infiltration schedule the same, and I would just show more hours 
with loads not met. My old standby DOE-2 has limitations for this type 
of situation obviously. These peak infiltration events are subhourly; my 
workaround is to group them into an hour, and the calibration to monthly 
bills is actually quite good.

Does anyone know of comparisons between similar buildings with these two 
types of "radiant" heat, or have experiences with actual installations, 
or other programs. The setpoint is already down at 60F so I'm not going 
to "simulate" one system as better than another by changing the setpoint 
down.

--
Fred W. Porter
Senior Engineer
Architectural Energy Corp.