STP SERIES Install, Operation, and Maintenance Manual
SECTION 3: OPERATION AND CONTROLS
Rev-1
Diversified Heat Transfer, Inc.
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439 Main Road, Route 202
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Towaco, New Jersey 07082
Page
21
of
97
STP Manual
PHONE: 800-221-1522
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WEBSITE: www.dhtnet.com
09/11/2019
3.3 PLATE OPTIONS
STP Series units’ heat exchangers are available in standard double-wall brazed plate
construction. Double-wall construction features boiler and domestic water separated by a n air
gap between two walls, rather than being separated by only a single wall. This g r e a t l y
e n h a n c e s protection against leakage of the boiler water into the domestic water. If there is
leakage in a wall, the water is collected within the air gap which is vented to atmosphere for
leak detection. Similarly, if the domestic water leaks through a wall, it is collected within the
air gap and is vented to atmosphere for leak detection.
3.3.1 Double Wall Construction and Protection Performance
The advantages of double-wall construction include:
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Prevention of cross-contamination
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Easy inspections and low maintenance
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Fully visible and vented leak detection between plates
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Potable water and heating medium are completely separated.
Leakage can be caused by corrosion, erosion, and vibration, and can result in the domestic
water system being contaminated by a heating medium, such as hydronic water, glycol
solution, etc.
There is no practical way to have the heating medium sterile or free from harmful treatment
compounds or corrosion by-products. A low pressure/temperature heating medium circuit
does not ensure contamination protection of indirect, single-wall water heaters. Whether they
are shell and tube, shell and coil, plate and frame, or any other type, all consist of relatively thin
wall heat transfer surfaces separating the heating medium from the domestic water system.
Therefore, the potential for cross contamination is real and in some instances contamination has
occurred.
Several states and cities are now insisting on double-wall vented construction in all indirect
type domestic water heaters. Plumbing codes have also been re-written to include double-
wall protection. See Figure 3-2 for an illustration of how a single wall and double wall differ in
construction, and how both function in the event of a hole, allowing fluid to leak through a plate.
