Martino wrote:

Many local HVAC companies just guess the size of the AC unit and therefore I
decided to run my new house data through a Manual J compliant software.
Depending on design summer temperature I obtain the following AC size (in
tons) recommendations

Summer Temp Size 1 Size 2
90F 4.76 6.02
95F 5.04 6.46
100F 5.32 6.89
105F 5.61 7.33

The house is being build near Seattle where the max summer temp rarely
exceeds 105F but gets to 100F for a week or so during summer. 90F can stay
with us for few weeks per summer.

I am a bit confused about two sizing recommendations:

Size 1 is based on sensible and latent heat gain
Size 2 is based on 75% Sensible Capacity

I do not want to oversize my A/C unit but I do not want to significantly
undersize it either. What do you think? Thanks.


First off, you have to use the summer design conditions for your area!
Washington, Seattle-Tacoma airport, Official listed Summer Design is 80
dry bulb & 64 wet bulb, or around a low 41% relative humidity.

Therefore, you are using Summer Design temperatures that are way too high!
Run the above 80-F dry bulb & 64-F wet bulb temps through your manual J
software, then tell us what you get.
How many square footage is your home? Did you figure the heat-gain
correctly?
The ductwork & airflow is critical to efficient operation!
http://www.udarrell.com/proper_cfm_b...syste ms.html

- udarrell

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WISDOM PRINCIPLED EMPOWERMENT COMMUNICATIONS -
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