Latest Discussions : HVAC

sfe391

07:45AM | 11/28/05
Member Since: 11/27/05
7 lifetime posts
Hello all:

I'm new to the board and hoping someone can help me. I have two conditioned zones in my house with a Janitrol GMP N0804 REV B in one and a Janitrol GMP 075-3 REV B in the other, both with matching cooling coils and condensers with a total of 5-1/2 tons of cooling capacity. My house is 3200 square feet, well insulated, double paned glazing etc., but the cooling has never worked very well. The supply air is quite cold, but the overall cooling is poor (eg. when its 90 degress out, the cooling has to run for 3 or 4 hours to get the interior temp to drop 8 or 10 degrees). So my questions are as follows:

1. Is the cooling capacity adequate for the house size?

2. Is there a way to increase the airflow to push more cold air? If so, is it something I can get the thermostat to switch so the increased air flow only comes with the cooling demand?

3. Is there anywhere on line I can get Janitrol literature for these two units?

Thanks in advance!

sfe391

08:51AM | 11/28/05
Member Since: 11/27/05
7 lifetime posts
Thanks for the reply. I realize that cooling load calcs would answer the load question, but I was looking for a rule of thumb answer. The house is 4 years old, tight, well insulated (R-19 walls, R-30 ceilings and floors), with about 18% dual glazing distributed about equally on the four orientations in a climate zone with a 1% cooling design temperature of 85 degrees, and relatively dry when cooling is required. Does anyone know if 5 to 6 tons of capacity is about right?

sfe391

10:19AM | 11/28/05
Member Since: 11/27/05
7 lifetime posts
Okay. For the lower zone, a UAdeltaT calc at a 1% design temp yields 4,200 btu/hr. The west glazing gains a max of 12,050 btu/hr per ASHRAE solar heat gain factors. I forget the specific heat and density of air, but even if you add fifty percent of the conductive gains for infiltration, and a like amount for internal gains, you still come up way short of 3 tons, which is what I have cooling the zone. So something does not compute. Am I missing something? Does anyone have a rule of thumb for air conditioning sizing?


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