We are generally warm and wet. When we do get cold, really cold, we are also very dry at least with regards to relative humidity.
Wood vs...Heat pump?
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We are generally warm and wet. When we do get cold, really cold, we are also very dry at least with regards to relative humidity.
If you look up the data sheet on your model and keep in mind that building heat loss increases as the outside temperature drops, this makes perfect sense.
At the seasonal design temperature of 47 degrees on mine, it achieves its rated 2 ton capacity of 24,000 BTU/hr. I think the installer chose a balance point (heat loss equals heat pump capacity) of 37 degrees, at which temperature the manufacturer rates the heat pump for a little over 20,000 BTU/hr.
Based on how the heat pump keeps up, I've noticed the actual balance point seems to vary between 30 and 36 degrees. When it's cloudy and calm, the heat pump keeps up at much lower temperatures. When it's windy or clear with dry air, (the latter maximizes radiant heat loss), I see the auxiliary heat kick in at higher temperatures.
So I'm guessing on average my actual balance point is around 33 degrees and the heat loss at that temperature around 19,500 BTU/hr.
At 15 degrees, which is a temperature we usually only see once or twice a year in this area, it's only rated for 15,000 BTU/hr. At that temperature, my heat loss is probably somewhere in the 25-30,000 BTU/hr range, so it's obvious why the auxiliary heat is needed.
Since the 15 kW heat strips are equivalent to 51,000 BTU/hr, it's also obvious how they're able to warm the house up so quickly when they kick on.
I haven't noticed the same with mine - I notice lots of defrost cycles when it's cold,regardless of humidity, and I think it was probably a design compromise - mine doesn't have a humidity sensor. I was recently thinking that would have been an upgrade that could allow a well programmed controller to better predict how often defrosts were really needed. It sounds like some may already have that feature.
JA600L
Minister of Fire
Just to clarify, at this point does the auxiliary come on at all? My heat pump will run too at those temps, but when it falls 2 degrees from the setpoint it kicks auxiliary on. Which is going to happen often at that temperature.
There is no auxiliary heater on my Mitsubishi mini split. When it gets that cold my wood boiler storage is charged up and the thermostat is set to a lower setpoint and that kicks in. I am not representing a 1 ton minisplit as a winter time solution in northern New Hampshire but I am impressed as to what it can put out. My house has a lot of passive gain on sunny days so the minisplit is getting help from the sun. I usually shut it down if its going to be below 30 at night and run the boiler and turn it back on in the AM.
There are minisplits and then there are conventional split system heat pumps that use an air handler and ducts. The technology is much farther advanced on the minisplits. The minis generally don't have backup resistance coils and can put out full rated output at 5 degrees above zero, the conventional heat pumps can't do that yet.
If you were super serious about using a heat pump to heat your home in temps below zero then you can do it by oversizing your equipment. There is always some heat to be extracted from the outside air. Much cheaper (equipment cost) would be a resistance heater of some sort that can kick on and make up the difference.
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There are more options than what has been posted. Do your homework it will be worth it. Lots of not so good info on this thread.
Ashful
Minister of Fire
Back to the original post:
I haven't seen natural gas mentioned as an option.
Dustin, do you have access to NG? I'm guessing "no" since your fireplace downstairs is propane. Given the glut of NG and how nicely it heats I'd consider it if available.
BTW, if the fireplace is a direct vent unit it can be quite a capable heater especially for backup. . Also, if propane now and NG becomes available it can be easily re-jetted for NG.
I haven't seen natural gas mentioned as an option.
Dustin, do you have access to NG? I'm guessing "no" since your fireplace downstairs is propane. Given the glut of NG and how nicely it heats I'd consider it if available.
BTW, if the fireplace is a direct vent unit it can be quite a capable heater especially for backup. . Also, if propane now and NG becomes available it can be easily re-jetted for NG.
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Ok. There are conventional heat pumps that modulate and work to below zero. There are ducted mini splits that work below zero. There are mini splits that replace conventional air handlers but still work like a ductless split. There are mini splits that heat water. There are heat pump water heaters. Some mini splits that work below zero but capacity is cut in 1/2 and cop is low. There are mini splits that work below zero with little capacity loss while retaining cop. There are mini splits that work below zero and retain capacity but have much lower cop. Each scenario has a different effect on the wallet. There are a crap ton of different units out there that you have to take your time and read every spec. Many make info misleading. For mini splits The larger the unit the less efficient it is, But with heat pump the larger the better for capacity reasons as it is hard to oversize anymore.
I have a ground source heat pump it cost about $800-$900 a year for heat and hot water ( winter months only for hot water ). Our electric rates are about .14 kw/hr. It cost about 20k to have installed including ductwork. I dont run the A/C much and have never noticed a cost associated with the A/C. I live in interior Maine our house is about 3000 sq/ft of conditioned space. It was not any more expensive then having a conventional oil or propane system installed along with central A/C and ductwork.
i have a heat pump in PA, its very cheap to run. I still burn as primary heat, but the heatpump covers the shoulder season, and is infinitely better than the oil in the house for the times I am not using the stove. highly recommend, relative to the oil, it paid for its self really fast, like 2 or 3 years, even with burning... oil is expensive. have a trane xr14, good unit
Late to the party but I have a few observations. An all electric furnace is typically installed with all metal non insulated duct work. It will sweat if a heat pump is running in cooling mode. This may or may not be the case here.Mini splits are nice but I've decided no to install them due to what I have seen at work. They are lined inside with Styrofoam that allows the growth of mold in areas that are inaccessible without complete disassemble. I have seen this in both ceiling mounted and wall mounted units. In the ceiling mounted unit I saw it when we took it apart to get to the blocked drain pan. In the wall mounted I saw it when it was cut apart to scrap the coil.
That is how we run our system as well. It's great for our several months of shoulder season weather. Our system is an American Standard Heritage 16.
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