[BLDG-SIM] Garage Heating

[Chris Jones]

Fred
I did some analysis for a very large warehouse with 10 bay doors on one 
side.  The design assumed two "zones".  The interior zone which included 
the envelop loads from roof, walls, slab edge, windows, etc.  The zone also 
heated the required ventilation air.  This was done by a gas fired roof top 
unit.  The second zone was the area adjacent the bay doors.  The problem I 
had was in determining first the depth from the doors affected by the doors 
opening and second the average air change rate per hour for occupied 
hours.  Radiant gas fired heating tubes at the ceiling were used.  These 
heat up fairly quickly.  The mechanical designer thought he had designed a 
large enough system but the dock workers complained that they were too cold 
during the worst days of winter.  I was called in after the fact and from 
my research I agreed with the designers assumptions for average air change 
per hour.  Do you have any additional thoughts about this kind of facility?



At 14:38 13/05/2005, you wrote:
>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.
>
>
>
>
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Chris Jones, P.Eng.
14 Oneida Avenue
Toronto, ON M5J2E3
Tel. 416 203-7465
Fax. 416 946-1005 



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