Effects of wind on ductless minisplit air-to-air heat pump
I have had my a Mitsubishi hyper heat ductless minisplit hvac system for my new home now for going on 3 winters. It is rated to put out approximately 32,000 btus/h depending on outside air temp. My home design heat load is a little under 20,000 btus/h, and that is at a little under 0F. Last week it was -19F and the my home stayed at the thermostat temperature setting of 68F. Now today I am standing in my home thinking I feel a cool draft when I realize that it is the air handler blowing not so warm air. Today it is 8F but it is blowing like crazy out and snowing. Right now my inside thermostat is set at 68F and is only maintaining 67F. I have noticed this happening numerous times. Does anyone else experience this. I almost thought that the wind might somehow aid in bringing more heat energy to the outside unit. After all isn’t that the function of the fan? My blower door test resulted in an ACH of .2 so I am pretty sure it is not an increase of air exchange due to wind. There is also no snow accumulation around my unit and it does have the pan resistance heater. I wish I had of known this as the wind blows pretty consistently all winter where we live.
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Replies
The wind shouldn’t hurt the heat pumps ability to operate. People feel a “wind chill” for two reasons: the wind evaporates moisture from your skin, which is a form of evaporative cooling, and the wind draws heat away faster than still air does. A heat pump is pulling heat out of the outside air, so the wind actually helps in this case.
What you’re likely seeing reduce your inside temperature is the wind is resulting in higher thermal losses from your house. Part of this is the increased air pressure against your house caused by the wind worsens any air infiltration leaks you may have, the other part is that the moving air results in more heat loss than still air.
You might want to check that the outdoor part of your heat pump isn’t clogged with snow. If it’s clogged, that would reduce its effectiveness.
Bill
>" Now today I am standing in my home thinking I feel a cool draft when I realize that it is the air handler blowing not so warm air. "
During defrost cycles the head will blow cool air at low speed for several minutes before returning to the full-on heating mode. When it's actively snowing the outdoor dew points can be pretty close to the outdoor air temperature, resulting in more frequent defrost cycles.
If the line sets to the head are in a conduit penetrating the exterior wall and he conduit is no longer well sealed, wind pressures can force outdoor air in through the conduit which an also affect how it functions. (But I'm betting on defrost cycle frequency/duration.)