How to size heat pumps for cold winters and hot and humid summers?
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How does one choose the optimal heat pump size for heating and cooling in an environment like mine in which winters can get quite cold and summers can be hot and very humid?
I’m worried that my unit will be sized correctly for heating, but oversized for cooling. Per this article (https://www.greenbuildingadvisor.com/article/undersized-minisplit-heat-pump), I understand an undersized heat pump is better for managing humidity, especially during shoulder seasons.
Here are my details and what I’m considering:
Winter design temperature = 10 degrees F
Summer design temperature = 85 degrees F
Climate zone 4A
No backup heat atm, heat pumps entirely for heating and cooling
Loads for a zone I’m designing for:
– Heating load: 21,500 BTU
– Total cooling load = 15,900 BTU (sensible load = 12,100 BTU; latent load = 3,800 BTU)
I’m considering this Fujitsu configuration:
Outdoor Unit Model #⁺: AOU18RLFC
Indoor Model #⁺: ARU18RLF
Rated Heating Capacity (Btu/h) @47℉⁺: 21,600
Rated Cooling Capacity (Btu/h) @95℉⁺: 18,000
Full ASHP specs: https://ashp.neep.org/#!/product/32101/10/21500/85/15900/0/11940/744865/1
This unit seems to be a good fit for my heating needs: 95% design load served (which is within the 90 – 115% recommended range), 97% annual heating load served, 90% modulating.
For cooling, it would serve 130% of my design load and 95% of my annual cooling load, 78% modulating. This seems oversized.
Will this under-perform from a cooling standpoint or is it fine? Am I correct in assuming that the more I bump up my heating capacity to get to 100% design load served, the more I will tend to oversize for my cooling needs? Am I sizing correctly for sensible vs latent cooling needs? Is the best solution to undersize for heating to nail my cooling needs and then figure out backup heat for the rest of the heating load (e.g., heat strips)? Am I overthinking this?
-Luke
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Replies
The unit you are considering is a variable speed unit it will ramp down to 3100 BTUs at 95° so oversizing your cooling load will not be a problem.
Consider adding the strip heat as backup heat so when the system does go down it is inconvenience and not a crisis.
Be sure the bid includes the Fujitsu thermostat.
Walta