California Electric Reheat

July 1, 2012

California Electric Reheat

“Reheat” is the term used by air conditioning engineers to describe the process of reheating supply air of a variable volume air conditioning system. In a variable volume system, all rooms get the same cool air from a main air handler.

If one or more of those rooms gets too cold, the air is locally heated to make the space comfortable. This reheat can be done with either electric heating coils or with hot water heating coils. Electric coils are less expensive to install but use electricity rather than gas (used to heat the hot water) as a fuel source.

In California, the use of electricity is strongly discouraged by the Title 24 energy code. Thus, electric reheat is prohibited in California.

There is an exception, however. When the Title 24 calculations are done in conjunction with other factors such as boiler piping loss, electric heat may meet the energy code. It would appear that the USGBC did a full energy model proving electric heat to be an efficient energy choice. And MEP Ninja was “shocked” to make this discovery.

Mark D. Robison, PE

2 Comments

  1. Alec Denson says:

    Seems a bit silly to have to reheat air which has been over-cooled, particularly with all the green energy six-shooters being fired in the air lately. In what scenarios is this likely to occur?

  2. Mark Robison says:

    Yes, indeed, this is an energy wasteful design. But it is very in-expensive to construct and it was the most common design prior to 1980. The HVAC industry developed VAV to improve on this situation.

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