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DHW Off Heating Plant via HX |
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rev. 2008-11-25
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DHW Off Heating Plant via HX |
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rev. 2008-11-25
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Existing Conditions
Heating plant efficiency upgrade, with sufficient capacity and turndown, will be undertaken first.
The existing domestic hot water heat source is inefficient or uses electricity, which is expensive, as the heat source. The nearby heating plant is equipped (or will be equipped) with much more efficient boilers and has enough extra capacity to satisfy the DHW requirement.
Retrofit Conditions
Rather than buying a dedicated high efficiency DHW boiler, the available heating plant capacity can be used. By installing a relatively inexpensive brazed plate heat exchanger and some piping, the cost of a new boiler can be avoided. A digital controller should be used to switch appropriately between reset control on space heating demand and aquastat control on DHW demand, and to cycle pumps off when not needed.
Further Benefits
If the boiler is modulating, the DHW load will not cause the boiler to short-cycle.