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  1. #1

    Dual Fuel control issue


    A Dual Fuel Hydro air system has been proposed using a gas Buderus boiler with the Logamatic control system and two 3 ton Carrier hi-eff series #19 Heat Pumps & a FE4AANF006 Fan Coil unit with the infinity control system installed in North Central CT. The Buderus indirect domestic hot water heating/storage system will likley also be installed at the same time. Question (s)--is or will there be any control issues between the Carrier Infinity system and the Buderus control system-? The intent is to use the heat pumps down to a yet to be detremined temp.--say 40 degrees--then swith over to the Buderus boiler for primary heating--is this possible with these two control systems-? Does the use of the boiler and the heat pumps make sense for this part of the country-? House--20 year old--two story-2800 sq. ft. Thanks

  2. #2
    Join Date
    Sep 2006
    Posts
    1,253
    I believe you are going to find that you can run your heat pumps down to a much lower temp before shutting them off - if you shut them off. With your setup, the two heat sources should be working together with the heat pumps providing the primary heat and the hydro coil system supplementing the heat pumps.

    Even considering the impact of the defrost cycles on the efficiency of the heat pumps they will still have a COP of about 2.5 at 27*F. COP is Co-efficient Of Performance which tells you how much energy you get out of the heat pump for how much energy you put in. In this example, at 27* for each BTU of energy (3,413 BTU for each kW) the heat pump consumes it puts 2.5 times the BTUs into your home.

    Your decision to lock out the heat pumps at some temp will be driven by fuel costs. Figure out what it cost to produce 100K BTU of heat with your boiler and the fuel it uses (propane or Natural gas) and the heat pump at different temps (heat pumps lose efficiency as the temps drop). Your contractor should be able to provide you with all the details and should help you figure this out.

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