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Combo DHW & AHU

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  rev. 2008-11-25        

Existing Conditions

An electric water tank presently heats the domestic hot water.

There are various electric baseboard heaters and electric forced air heaters in the facility.  Electric resistance heating is a very expensive and should be minimized or replaced with another fuel source.

The purpose of the heaters is to add heat in the stairwells and service rooms that are not served by the air handlers.

Retrofit Conditions

It is recommended that a high efficiency natural gas hot water heater be installed in the facility.

It is also recommended that an air handling unit be installed in the ceiling space, complete with ductwork to each area of the facility [except xxx].  The water heater will be piped to supply hot water to a heating coil in the air handling unit, as well as satisfying domestic hot water needs.  A programmable thermostat will control the air handler.

When using potable water for heating, the installation must conform to accepted plumbing practice and local codes, including the use of copper piping.  This type of installation is commonly referred to as a "Combo" system.

It is recommended that the electric heaters be equipped with local electric controls to turn them off during unoccupied times, and when the outdoor air temperature is greater than 10°C.  A commercial quality setback thermostat with an outside air sensor can be used.  Where occupant adjustability is not desirable, ensure the setback thermostat includes security lockout functions.  Where vandalism or tampering are a problem, use a Honeywell T775 controller and timer, located remotely from the space sensing element.

Further Benefits



Application Details


Issues and Concerns







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