Hydronic/heat pump

[Morrelli]

I've got an LP HWH that is source for two hydronic air handlers. Also have central air utilizing the same air handlers tied to two older A/C units. zoned upper/lower. I'm thinking about a heatpump retrofit as I'd rather let the solar panels power a heatpump instead of burning LP for the heat and electric on older inefficient A/C units. I would install a tankless Navien with bypass recirc for DHW as I have some long waits for hot water and no way to put in a dedicated return recirc line.

A few questions:
Am I drunk?
Can I use the existing air handlers?
Should there be any consideration for a heatpump water heater in this picture and just upgrade the A/C units ?

Northern California Sierras Weather, hot summers and rarely gets below freezing in the winter, occasional snow.

my objective is to have solar carry the cooling and heating load. I know there is a lot of missing info, but do you think even contemplating such a retrofit is feasible?

Thanks in advance....

 

[John Gayewski]

You'd need a heat loss calc to find out if it's feasible. A heat pump water heater wouldn't be able to keep up with the load in heat pump only mode and would likley need to use its electric backup elements. That's just a guess, but I could very well be wrong as your load could be way smaller than I think. Either way the duty cycle on a water heater isn't designed to heat a house.

There are air to water heat pumps designed for space heating with radiant or air to air heat pumps for ducted forced air systems which should work fine for your purposes.

I guess you didn't really say if you have forced air or radiant. Why go from water to air?

 

[Sponsor]

 

[Morrelli]

You'd need a heat loss calc to find out if it's feasible. A heat pump water heater wouldn't be able to keep up with the load in heat pump only mode and would likley need to use its electric backup elements. That's just a guess, but I could very well be wrong as your load could be way smaller than I think. Either way the duty cycle on a water heater isn't designed to heat a house.

There are air to water heat pumps designed for space heating with radiant or air to air heat pumps for ducted forced air systems which should work fine for your purposes.

I guess you didn't really say if you have forced any radiant. Why go from water to air?

Thanks for the response. I'm not sure what you mean by "forced any radiant". the current unit is forced air over hydronic coils, ducted fed by a large HWH, which seems to be a boiler almost. it's a heater like none I've ever seen. runs at 150f. also supplies DHW. I thought a heatpump HWH would draw on electric as a given. I'll need to further educate myself on how those units work. sounds like an air to air heat pump would be the option. the space is so tight on third floor with this setup. for the life of me I don't understand why the contractor/owner builder located things as he did back in 1999. just to pull this huge HWH out will require opening a wall. pics attached. the water heater is tucked into a small opening down and to the left of the insulated "hallway" for lack of a better term.

 

[wwhitney]

See, e.g., Chiltrix:

Air To Water Heat Pump Manufacturer | Air To Water Small Chiller Heat Pumps & Air Conditioners | Residential Home & Server Room Chillers | Chiltrix Inc.

For an air to water heat pump to be very efficient for domestic space heating, you want the hydronic to air system to be designed to operate with 100F to 120F water, not 150F. So it doesn't sound like a drop-in replacement for your LP heater. Although if your fan coils are oversized you might find that they would still provide sufficient heat flow at a lower water temp.

Cheers, Wayne

 

[Morrelli]

See, e.g., Chiltrix:

Air To Water Heat Pump Manufacturer | Air To Water Small Chiller Heat Pumps & Air Conditioners | Residential Home & Server Room Chillers | Chiltrix Inc.

For an air to water heat pump to be very efficient for domestic space heating, you want the hydronic to air system to be designed to operate with 100F to 120F water, not 150F. So it doesn't sound like a drop-in replacement for your LP heater. Although if your fan coils are oversized you might find that they would still provide sufficient heat flow at a lower water temp.

Cheers, Wayne

Thanks Wayne -

 

[Fitter30]

Going with hp air handlers would be replaced system would different refrigerate and A coil. There's other ways of getting dhw to a faucet. Sounds like good plan might want to consider hp water heater.

Hot Water Recirculation for US

Hot Water Recirculation for US Test

www.grundfos.com

 

[Morrelli]

Going with hp air handlers would be replaced system would different refrigerate and A coil. There's other ways of getting dhw to a faucet. Sounds like good plan might want to consider hp water heater.

Hot Water Recirculation for US

Hot Water Recirculation for US Test

www.grundfos.com

With a HP water heater feeding the air handlers- do the handlers require a separate loop? if I put something like a grundfos comfort on the tank without a dedicated return, how do I isolate the two so the recirc isn't fighting the loop for the handlers? sounds like some control would be needed. if I'm.using a heatpump water heater, can I utilize 55 degree water to assist in any cooling across the handlers? sorry to go long. think my brain is going in too many directions on this...

 

[Fitter30]

Using a dhw for heating and hot water is not recommended because water sits in the air handlers and piping all summer long and can possibly grow bacteria. Hp water heater wouldn't keep up with the heating load of the house. Can't use 55° water to help with the ac load in the same air handler with a refrigerate coil.

 

[Morrelli]

Using a dhw for heating and hot water is not recommended because water sits in the air handlers and piping all summer long and can possibly grow bacteria. Hp water heater wouldn't keep up with the heating load of the house. Can't use 55° water to help with the ac load in the same air handler with a refrigerate coil.

ah, OK. so an alternative for DHW if using the HP WH specifically for the handlers function. ie. a navien tankless or the like?

 

[wwhitney]

If you're thinking of using an unducted self-contained heat pump tank water heater with the heat pump built in on top of the tank, you can't plausibly use that for space heating unless the unit is outside the house's thermal envelope. If it's inside, you effectively have resistive electric heating--the heat pump will take heat from the inside air, put it in the water, the water will go to a fan coil that puts the heat back into the air, etc. A resistive heater would do the same thing at much less expense and no moving parts to wear out.

Sounds like you need a good HVAC design professional, which means not just your typical HVAC company.

Cheers, Wayne

 

[Fitter30]

ah, OK. so an alternative for DHW if using the HP WH specifically for the handlers function. ie. a navien tankless or the like?

Any condensing boiler is only 95% efficient with return water temp under 140° above 87%.