Dual Fuel vs. Heatpump with Hydronic Coil Backup Heat

johntrhodes81

Just wondering if anyone had any thoughts on Duel Fuel Heatpumps vs Heat pump with Hydronic Coil Backup heat. Both would be propance backup: propance furnace or mod-con boiler running on propane. The boiler option would allow indirect hotwater, where the dual fuel wouldn't. Also the boiler option could be used for pool heating where the dual fuel couldn't. I am in SE PA, but have not yet performed a load calc but will on my 3,600 sq.ft. house.

Thanks,
John

hot_rod

Are you talking about an air to air heat pump?

you could consider an air to water heat pump which gets you a hydronic source that could provide heat, cooling, DHW. Some pool heat could be pulled when it is in cooling mode, instead of DHW

For dual fuel, use a gas furnace with a hydronic coil that could heat or cooling from the A2WHP

johntrhodes81

Sorry to be unclear but yes an air source heatpump. I was thinking either a dual fuel setup with switching over to a propane furnace or a propane boiler and water coil so the heatpump could run down to the economic balance point with the coil supplying supplemental heat when the heatpump can't keep up or after the heatpump shut down due to outside temp.
A water source heatpump seems to high an initial cost to get a pay back?
Johm

Hot_water_fan

A water source heatpump seems to high an initial cost to get a pay back?

Almost always

I don't know your electricity cost, but if it's around average ($.13/kwh or so), I doubt there will ever be an economic balance point to switch over to propane. Propane could be a backup, but it's operating cost will likely always be higher. So maybe skip the boiler entirely?

johntrhodes81

Its 14 cents here.  Propane gives twice the btus per dollar as electric heat strips.  I need another heatsource other than straight heatpump. Dualfuel would likely mean more propane usage since the temperature to switch would be higher.  The boiler route would let the heatpump run to a lower outside temp providing some of the btus needed to heat the house.

Hot_water_fan

I don’t see a compelling economic use for propane here - a cold climate heat pump (which work down to the negative teens) + electric resistance of some flavor should come in both less expensive up front and over time. SE PA is a relatively mild heating climate, you might never need the heating strips (or a small % of the year). If $.14/kwh at 100% = $41/MMBtu and propane is half that, you’ll only need a heat pump with a COP of 2 to be cheaper, which is about every heat pump at nearly every outdoor temp. We can solve the pool heating and DHW another way, like the Air to water system mentioned above. 

johntrhodes81

Ok. What type of heatpump are you discussing. I am not familiar.
Thanks 

Hot_water_fan

If you mean a cold climate heat pump, then something like this:

http://mylinkdrive.com/USA/M_Series/R410A_Systems-1/Indoor_Equipment-3/Multi_Position_Air_Handler-2/SVZ_KP_NA_Models/SVZ_KP36NA?product

Fully ducted, just like a furnace. There are other manufacturers out there as well. Depending on your heat loss, you might not need a cold climate version and could easily just use a Trane/Carrier/whatever and supplement it with electric strips. Just because a dual fuel set up might save on operating costs doesn't mean it's worth the upfront investment, as the balance point might be a temperature like 10 degrees, which you might spend only handful of hours at per year. Dual fuel with propane (since it's so expensive) doesn't make much sense. Dual fuel with natural gas is another story.

TAG

Have had numerous weekend place in Bucks County over the years ... one in Chester. For overall comfort I normally install a furnace along with the heat pump .... my last couple projects have used the Carrier 5 speed Heat Pump with infinity control --- modulating furnace. My new place is overkill -- full Carrier set up - boiler for radiant and the indirect. When propane was $1g ... Propane was cheaper. My electric is a bit more than yours ... my last propane fill was last week at $2.69g. The modern heat pumps can do the heating .. I'm just a bit of a chicken and we do leave the property often for a week at a time and turn down the heat. This way if we decide to come on short notice the furnace is there. I like the furnace in the coldest weather

IMO -- The boiler for just one coil is silly. First the boiler may not condense at the temp the coil needs and the overall cost of the setup is high .... the furnace will give you more control and higher efficiencies.

How much water do you need to heat .... they do make heat pump water heaters. There are propane on-demand. I always went propane tank. We always have a gas stove