Mini Split and Range Hood
I have an odd scenario with my Daikin mini split heat pump. Here’s the setup: heat pump upstairs with 2 heads (one for each bedroom), large range hood on the main floor. The range hood is probably oversized but it does a fantastic job moving kitchen related smoke and odors out. The issue is when the range hood is running to makes the heat pump in one of the bedrooms run too. The heat pumps are actually always on and set to about 69 degrees, but he 69 degree setting does not seem to matter. When the range hood is on and the bedroom temperature is 75 it will still trigger the heat pump to run. This only seems to happen in heat mode. My guess is has something to do with the air draw or movement? Any ideas?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Bryan,
One obvious possibility is that the biggest air leak in your house is in the bedroom. When you turn on that big honking fan in the kitchen, you depressurize the house, and cold air rushes into your house through leaks in the thermal envelope. This makes your house colder. Responding, your ductless minisplit cranks up.
I think Martin is right but the fan is pulling cold air in and across the temperature sensor for the mini split. The fan may not change the temperature of the room enough for you to feel but even a small draft near the mini splits sensor will make it run.
Try turning off the mini split and turn on the fan then use the smoke from a burning incense to find your leaks?
Walta
Walter, where should the air be coming from? Will it pull it through HRV ducting / intakes if the house is well sealed?
Walter,
I agree with your analysis. All that is necessary for the minisplit to come on is a cold breeze near the temperature sensor at the air intake location.
Stephen,
An HRV is not a makeup air unit; it is designed for balanced operation (air in = air out). For more information on this issue, see Makeup Air for Range Hoods.
Thanks Martin. I read that article. Luckily, we're playing with a much smaller range hood, a mere 200 CFM. We also have an HRV exhaust duct into the kitchen. Does it stand to reason that for low cooking loads, we could run the HRV on high to help remove odours and moisture from the house, instead of flipping on the hood fan?
Stephen,
It's your house, and you can operate your house any way you want. If operating the HRV achieves the result you want, without operating the range hood fan, then there is no reason not to do what you want.
The only risk to your method is that pulling smoke into your HRV core is not good for the HRV. That's why the grille for the exhaust duct on your HRV should never be located near your kitchen range. If your cooking results in lots of smoke, using your range hood exhaust fan might still make sense.
Stephen,
IMO the juice isn't worth the squeeze by altering how/when you use your range hood. Evacuating humidity and other substances related to cooking is significantly more important to occupant health rather than the couple of pennies spent in electricity when the minisplit turns on.
btw... 200 cfm range hood fan doesn't sound oversized by any stretch.
Betcha a nickel there is a ferocious air leak where the umbilical goes through the wall to the mini split
Bryan,
I am not sure about the Daikin units, but a Mitsubishi installer told me last week something along the same line as Keith above - the penetration in the wall for the "umbilical cord," or bundle of wires, condensate line, and refrigerant line, is a considerable sized hole. And ironically enough, the temperature sensor for the indoor cassette is right on top of this penetration. It stands to reason that when the range fan runs, and pulls in outside air through the cracks, it is pulling air around the umbilical penetration and cooling the temperature sensor and calling for heat. I would suggest checking the air sealing details at this location. It seems easy enough for the handy homeowner to do.
Thanks for everyone's response. I will check the hole for leaks and fill with foam where appropriate.