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  1. #14
    Join Date
    Apr 2004
    Posts
    7,680
    Unfortunately no, because heat would be removed from the water and you would have to burn gas to heat it. hydronic heat costs just a tad more than the gas that it costs to heat it. (pump).

  2. #15
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635

    Doc

    I did a google search and came up with a study (It might have been Home Energy Magazine. I'm not sure.) that showed delivered COP from actual homes. Given the typical poor installation and maintenance practices out there I'm not surprised by the low COP. Given what I've seen as a repair man I expect it. I can't tell you how many times I've seen a heat pump that was running only on its electric heat strips for an entire winter and the customer didn't even know it. They just paid HUGE bills. Events like that bias me towards gas. Gas furnaces are a little more idiot proof than heat pumps.

    The electrical usage of the blower in a gas furnace is a fair point. But it doesn't cover the gap. I'm not sure what numbers you're using. But the rates I posted are from my own personal utility bill. Just as when 5 cents per kWh makes the heat pump a no brainer, so too does 17 cent per kWh make gas a no brainer (for the moment). Obviously that's a very unique situation to our local market and could easily change.

  3. #16
    Originally posted by docholiday
    Unfortunately no, because heat would be removed from the water and you would have to burn gas to heat it. hydronic heat costs just a tad more than the gas that it costs to heat it. (pump).
    I think "ct" meant, wouldn't using your gas water heater instead of electric heat strips be a good source for backup heat for a heat-pump installation. This is what I had in mind, since I already have/need a gas burner to heat water.

    Yes, a gas water-heater hydronic backup (for forced-air heat pump) is less efficient than a conventional gas furnace dual-fuel setup, but it's got to be better than electric resistance. Again, in our climate, the backup isn't going to be called on all that often, maybe 20 days out of the year.


  4. #17
    Join Date
    Sep 2004
    Posts
    3,157
    Again, in our climate, the backup isn't going to be called on all that often, maybe 20 days out of the year.
    ------------------------------------------------

    Even here in Sunny calif we have periods of cold wet weather (fog) for every bit of 20 days . When that fog rolls in it may only be in the 40's but that heat pump will be burning every electric strip you can give it . In that type of weather I dont think a heat pump would be cost effective at all

  5. #18
    Join Date
    Apr 2004
    Posts
    7,680
    Sorry I misunderstood. I see what you mean now.

    Worth thinking about. Remember though, your hot water is only about 120 degrees. I'm afraid the size of the coil would be prohibitive and restrictive to your airflow when your looking for efficiency year round. Maybe one of the hydronic guys would share with us what the option would be.

  6. #19
    Chironian:

    One system is the Apollo by A.O. Smith. Their system uses an oversized quick recovery gas water heater connected by a circulating hot water loop to an air handler. The air handler has both an AC coil and a hot water coil. The sytem is typically set up so that the gas water heater provides the heat during the heating season. I'm pretty sure that it could be hooked up with a heat pump and use the gas heat in place of the heat strips as auxiliary and emergency heat.

    My own home has an oversized gas water heater,50 gallon quick recovery(there's only two of us) hooked up to an aquecoil hot water coil and circulator pump located at the discharge end of our heatpumps air handler. It's set up so that when the heat pump calls for auxiliary heat the circulator motor comes on and hot water from the water heater provides the auxiliary heat. If we wanted to we could select "emergency heat" on the thermostat and bypass the heat pump operation and just run the hot water coil.

    The secondary hot water coil does create addtional restriction for the air handler to overcome(a second coil) and therefore their may be issues dealing with insufficient air flow if not engineered correctly...hence an advantage going with a system such as the Appolo. If the second coil is taken into the design process your less likely to have any problems.

    My system works fine as the aqecoil hot water coil doesn't seem to be too restrictive to flow.

    The downside to the system is without some modification the gas water heater is putting out 135-140 degree hot water through the coil as you don't want your domestic hot water to be any hotter to prevent scalding. With a little modification your hot water can be set up to provide hoter water to the hot water coil and a lower temperature water for domestic.

    [Edited by roadking321 on 10-09-2005 at 08:41 PM]

  7. #20
    Join Date
    Sep 2004
    Posts
    3,157
    My own home has an oversized gas water heater,50 gallon quick recovery(there's only two of us) hooked up to an aquecoil hot water coil and circulator pump located at the discharge end of our heatpumps air handler. It's set up so that when the heat pump calls for auxiliary heat the circulator motor comes on and hot water from the water heater provides the auxiliary heat. If we wanted to we could select "emergency heat" on the thermostat and bypass the heat pump operation and just run the hot water coil.
    ------------------------------------------------------------

    I could have made a million on that idea if soeone hadnt thought of it first.

    even air being blown across a 120 degree coil should fel every bit as warm as the air would feel with a heat pump (I think)

  8. #21
    My water heater is set at 135 degrees. Temperature at the supply vents is about 25 degrees less...therefore, 110 degrees which is usually 20-30 degrees warmer than typical heat pump temperatures. My previous home had a gas pack and the temperature from the vents was warmer...about 125-130 degrees or so. As many have noted the warmer temperature created shorter run times and uneven tempertures within the home...although that nice blast of very warm air felt reassuring on a cold winter night!

  9. #22
    Join Date
    Apr 2004
    Posts
    7,680

    Re: Doc

    Originally posted by Irascible
    I did a google search and came up with a study (It might have been Home Energy Magazine. I'm not sure.) that showed delivered COP from actual homes. Given the typical poor installation and maintenance practices out there I'm not surprised by the low COP. Given what I've seen as a repair man I expect it. I can't tell you how many times I've seen a heat pump that was running only on its electric heat strips for an entire winter and the customer didn't even know it. They just paid HUGE bills. Events like that bias me towards gas. Gas furnaces are a little more idiot proof than heat pumps.

    The electrical usage of the blower in a gas furnace is a fair point. But it doesn't cover the gap. I'm not sure what numbers you're using. But the rates I posted are from my own personal utility bill. Just as when 5 cents per kWh makes the heat pump a no brainer, so too does 17 cent per kWh make gas a no brainer (for the moment). Obviously that's a very unique situation to our local market and could easily change.
    Well you have a point, an improperly installed or set up heat pump can be costly to operate. Fankly its inexcusable. And I respect your preference, but for the sake of this thread, I still think Nathan would be far better off with a heat pump than a way oversized gas furnace just so he can have the blower for his large a/c requirements. Remember he only has like a 50k heating need but 5 tons of cooling.

  10. #23
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    Originally posted by docholiday
    Remember he only has like a 50k heating need but 5 tons of cooling.
    Actually I don't remember. Was that from a different thread? If so, a two stage furnace would be the ticket IMO. It's different in California. ;^)

  11. #24
    Join Date
    Sep 2004
    Posts
    3,157
    50 k of heat , and 5 tons of cooling? is this a mobile home?
    if it is we are talking about a different ball game all together

  12. #25
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    No mobile home. Just a hot dry climate with very mild winters.

    I am going with 2 stage furnaces and VS, but I'm still going to be oversized on heating.

    Thanks for some very interesting responses. I've learned that there may be better solutions to many of the HVAC situations that are encountered, but local HVAC dealers still have to do the work, and it is quite a challenge to locate anyone willing to try something new.

    Many local dealers resist R-410A systems, zoning, even load calcs, etc. The dealer who is installing my system (Bryant) is reluctant to install an Evolution control, even though the product has been out for quite some time and it well regarded by the participants on this forum.

    I'm sure it's the same with many different types of businesses.

    Thanks again.

  13. #26
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    A customer that's demanding more expensive equipment and a contractor that's resisting? There must be something in the water down there.

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