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120F source for domestic hot?

Eric Snow
Eric Snow Member Posts: 2
I am new to the board here, and was directed by a mfg's rep to this wonderful site. I am an engineer and working on a solution for my home domestic water. I will be using an air to water heat pump when they hit the market (www.nyletherm.com) soon. This heat pump is a two stage (series) unit that will produce ~10 gpm of 120F hot water and add at least 40,000 BTU's. Additionally code requires me to have a back up method of heat, which will be a small direct fire tankless hot water heater. In order to use the heat pump for cooling I think (not done researching Authorities Having Jursdiction issues) I need a primary or system loop and a domestic hot water loop seporate from the system.

My question is the best way to use the heat pump to provide domestic hot water until the water demand exceeds the heat pump (or storage volume) capacity.

Solution #1
System water supply to the hot water service using a Taco type circulator. In series located between the circulator and the hot water heater (possibly a amitrol boilermate type unit) will be the code required back up heat, a tankless propane unit. Unit will fire (normally) when domestic water drops below 110F or so.

Possible problem with #1, this adds heat to the 'system' water and is really some thermal distance away from the hot water (going through the boilermate).

Solution #2
Locate a plate heat exchanger on a different loop with the b/u heat source. Maybe pass all the water from the boiler mate through a plate exchanger before the water goes to the boiler mate. I heard about Takagi having a unit that could heat system water and domestic water, any ideas would be appreciated.

Comments

  • don_85
    don_85 Member Posts: 2
    No need to reinvent the wheel.

    > I am new to the board here, and was directed by a

    > mfg's rep to this wonderful site. I am an

    > engineer and working on a solution for my home

    > domestic water. I will be using an air to water

    > heat pump when they hit the market

    > (www.nyletherm.com) soon. This heat pump is a two

    > stage (series) unit that will produce ~10 gpm of

    > 120F hot water and add at least 40,000 BTU's.

    > Additionally code requires me to have a back up

    > method of heat, which will be a small direct fire

    > tankless hot water heater. In order to use the

    > heat pump for cooling I think (not done

    > researching Authorities Having Jursdiction

    > issues) I need a primary or system loop and a

    > domestic hot water loop seporate from the

    > system.

    >

    > My question is the best way to use the

    > heat pump to provide domestic hot water until the

    > water demand exceeds the heat pump (or storage

    > volume) capacity.

    >

    > Solution #1 System water

    > supply to the hot water service using a Taco type

    > circulator. In series located between the

    > circulator and the hot water heater (possibly a

    > amitrol boilermate type unit) will be the code

    > required back up heat, a tankless propane unit.

    > Unit will fire (normally) when domestic water

    > drops below 110F or so.

    >

    > Possible problem with

    > #1, this adds heat to the 'system' water and is

    > really some thermal distance away from the hot

    > water (going through the boilermate).

    > Solution #2 Locate a plate heat exchanger on a

    > different loop with the b/u heat source. Maybe

    > pass all the water from the boiler mate through a

    > plate exchanger before the water goes to the

    > boiler mate. I heard about Takagi having a unit

    > that could heat system water and domestic water,

    > any ideas would be appreciated.



  • don_85
    don_85 Member Posts: 2
    No need to reinvent the wheel.

    have you looked into heat recover option? Most water to air
    heatpump manufacter have this option.

    The hot water is provided by a circulating water from your existing hot water tank thrugh the heat recovery coil and asorbing the heat that would normally be rejected by your
    heatpump.This will be the same heat that is absorb from your home during the cooling season.

    Not that great in the winter months but, works great in the summer.
  • Scott Gregg
    Scott Gregg Member Posts: 187
    Hot water

    If you come from your heat pump through your tankless and it is a Noritz model set at 125* or 130* if you are getting hot water into it at 120* it just will not fire. Once the incomming water temp drops about 15*, it will fire up and heat the water the rest of the way. A model N-069M will give you 7.9GPM at this rate.

    A couple more things, if your house is piped with 3/4" PEX or CPVC water lines, you will not be able to flow more that about 10GPM total anyway. It is very rare for a house to need more than about 6GPM of hot water at a time unless you have a body spray system or high flow tb filler and even then you are limited in actual flow by the pipe size installed.

    A "small" tankless may yeild less than desired results. I would use anything smaller than the Noritz N-069M.
  • Eric Snow
    Eric Snow Member Posts: 2


    The house is a 1930 cottage plumbed with I think everything except PEX. While doing the remodel I am going to re-plumb everything in PEX from a central manafold. One quirk about the local AHJ is they size the incomming water line to a domestic pex manafold based on how many goes-outs it has. Thus if I have the eight I plan on using now (and four more added later when we have the $ to add a master bath) I would need a 1 1/4 inch PEX supply to the manafold.

    Anyway I just want to be able to run two shower heads and have someone turn on a thrid fixture (sink or something) briefly and not affect the temps in the two showers. I am guessing at the 7 gallon figure for that number.

    We don't have huge body sprays or jetted tubs. Heck the only insulation on three of my exterior walls (going to be fixed during construction) is what the mice have dragged in. We live in the country!
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