Heat Pumps without much redundancy in cold climate?

[Maine Way]

I have recently begun to consider mixing Heat Pumps into the HVAC design of a remodel. They were suggested as a way to control humidity, and it seems they could have many benefits - heating, cooling, air quality).

Looking at LGRED technology, manufacturer indicates full heating capacity down to outside temps of 4F and continued operation down to -13F. It is very tempting to leave the baseboard heat out of the bedrooms and rely on the heat pump.

In the worst situation, I could plug in an electric heater when its continuous very low temperatures. I would still have a boiler which would serve radiant zones downstairs and perhaps some cast iron baseboard downstairs. I'd add a kick space heater to bathrooms off the boiler to give individual room control of heat there.

It seems as though the heat pump would do 98% of the heating for those rooms and I can avoid the clunky cast iron. And, probably save on heat...

Thoughts?

 

[John Gayewski]

What you save in money you will give up on comfort. This a a trade off. The heat pumps use electric resistance to keep up at which point you lose lot of savings.

This is personal decision. I personally like to be comfortable in the winter heat pumps don't feel as comfortable when not using resistance.

Manufacturers make claims based on laboratory conditions and high winds usually aren't taken into account.

That doesn't mean they can't be useful. Cooling and humidity control are good things. But for heat alone I'd prefer radiant heat in the bedroom.

 

[Sponsor]

 

[Fitter30]

Heat and cool with two mini split systems 2ton units with each having 3 indoor wall units. 1900 sq ft 3 bed 2 bath modified A frame. In southern mo. 6* can heat with only one system 68*. Have two systems and propane fireplace for backup. No strip heat. The higher efficiency systems eliminates 3/4 of residential service people two main reasons lack of factory training ,laptop with the correct program and computer knowledge.

 

[CenterTree]

Are you talking mini-splits or a regular unit?

We have a Carrier GreenSpeed variable speed system (both AC and Heat pump). Love the AC portion! It does a good job at removing humidity.

The heat side can be efficient (when it works). He's my biggest complaint from heat pump heat. It doesn't really feel like HEAT. Yeah, it gets the house up to temp and maintains it fairly even. However, we always feel unsatisfied by the lack of warmth. Like John said, just not a comfortable heat, as there is always air moving that feels lukewarm.

Not familiar with the LGRED, but our CARRIER air handler has heat strips built in so that when the temps get too low for the heat pump to be efficient, they come on to make up for the lack of heat. This adds a great deal to your energy bill!
We can actually FEEL the difference when the supplemental heat strips kick in as compared to just the pump. (at about 7 degrees for us).



AC: GREAT!

Heat: MEH.



Also, as fitter mention... I agree, you may have trouble finding competent service people for these systems. Our installers are always on the phone with CARRIER direct when they come to do service.

 

[WorthFlorida]

Heat pumps of today can work really good at lower temperatures but as stated above, you cannot rely on heat pump alone. Conventional HVAC heat pump with an air handler has an "Aux" source of heat (second stage heat) such as fossil fuel or electric heat strips. It's the Smart Thermostats does most of the decision making when to activate the AUX heat when needed. Using the outside temperature from a local weather site, the set temperature and the room temperatures are used. Most thermostats when the set temperature is more than two or three degrees above the room temperature, the aux heat will be turned on. If it is only one degree usually only the heat pump is activated. Some thermostats allow the the second stage to be programmable when to activate by setting the degree difference. Smart thermostats can allow you the use heat pump only, aux heat only or both.

 

[Maine Way]

These have been helpful replies and I suppose confirmed what I knew. It just seemed that the heat pumps could mostly do the job already, so it was getting stupid to put so much into a MOD CON system, especially since I still have all that cast iron BB to install. But, the comments are really good...the BB heat will be more comfortable heat and perhaps the heat pumps do the duty in lighter, shoulder seasons (and of course can dehumidify and cool as well in summer).

 

[Dana]

These have been helpful replies and I suppose confirmed what I knew. It just seemed that the heat pumps could mostly do the job already, so it was getting stupid to put so much into a MOD CON system, especially since I still have all that cast iron BB to install. But, the comments are really good...the BB heat will be more comfortable heat and perhaps the heat pumps do the duty in lighter, shoulder seasons (and of course can dehumidify and cool as well in summer).

Be sure to not oversize the modulating heat pumps either, or they won't do what you want them to do. To dehumidify they need enough load to run at a high enough modulation level to get the coil temps to a low enough temp, and high enough duty cycle to wring out a significant amount of moisture.

Run an AGGRESSIVE Manual-J type load calculation (online freebie tools such as coolcalc or loadcalc are fine, if you're aggressive enough on input data) and when in doubt between sizes go for the smaller rather than larger.

 

[ArayT]

As others have said, would not recommend it. Heat pump provides heat in two ways, what it captures outside and heat of compression. With what you have available outside, that just isn't enough.

 

[Jadnashua]

While this is an old thread, one thing that can affect the overall comfort is the fan speeds available. In the summer when cooling, a higher fan speed can help with overall comfort, but it can mean that in the winter, especially when the outside temperature is low, that higher fan speed can mean you get wind chill as the air moves across the heat exchanger too fast to heat up much. While the measured air temp may be in the desired, thermostat set value, the high fan speed can make things feel cooler (aka, a draft). So, if the air handler is not smart enough, you may need to manually slow it down some when heating.