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Quotes - Engineering - SalesHeat Exchangers For
Domestic Hot
Water Systems
Domestic hot water duty is thermally undemanding and administratively exacting. The load is spiky, the temperatures are modest, and the water being heated is drinking water.
That last fact is what drives the selection. Where a boiler, steam or glycol circuit heats potable water, many jurisdictions require double-wall construction, and the DSU, DWU, DTCS and DTCW ranges exist to provide it.
Double-wall requirements vary by jurisdiction and by the authority having jurisdiction. Confirm before ordering, because single-wall and double-wall ranges are not interchangeable.
Request a QuoteDomestic Hot Water Systems
Demand Is Spiky, Not Steady
A hotel at seven in the morning, a school at lunchtime, a stadium at half time. Domestic hot water load arrives in short heavy peaks separated by long quiet periods, and the system has to be designed for the peak while behaving sensibly between them.
That is why storage and recovery are usually a paired decision. A larger tank with a smaller heater, or a smaller tank with a faster one, can both serve the same building.
Instantaneous or Storage
Instantaneous heating sizes the exchanger for the peak flow and eliminates stored volume. Storage sizes the tank for the peak and the heater for recovery between peaks.
Instantaneous is compact and demands good control; storage is forgiving and takes floor space. Most commercial buildings end up with some storage because the peaks are too sharp to follow.
Double-Wall Is a Consequence Decision
Tube failures are uncommon. The question is what happens if one occurs and nobody notices for a week. Where the answer involves drinking water in an occupied building, the arithmetic favours double-wall construction regardless of how reliable a single tube is.
It costs surface area and therefore money, because the interface between the two tube walls is a real thermal resistance.
Scaling Follows Surface Temperature
Hard water scales preferentially on the hottest surface, which is the tube wall. Using steam at high pressure produces a wall temperature far above the water target and accelerates scaling considerably.
Lowering the medium temperature and adding surface reduces the scaling rate more effectively than any amount of water treatment on the same system.
What We Need to Size a Domestic Hot Water System
The peak draw and how long it lasts. Domestic hot water demand is spiky rather than steady, and a hotel at seven in the morning is a completely different problem from the same building at midday. Send the peak flow in GPM and its duration, not an average.
Whether there is storage, and how much. A tank absorbs the peak and lets a smaller heater refill it between draws; instantaneous heating sizes the exchanger for the peak itself. Both work, and the choice usually comes down to the floor space available against the sharpness of the draw profile.
The heating medium and its temperature. Steam gives the fastest recovery and the highest tube wall temperature, which matters on hard water because scale forms preferentially on the hottest surface. A lower medium temperature with more surface runs considerably cleaner over a building's life.
And the local double-wall requirement. Where a non-potable circuit heats potable water, the DSU, DWU, DTCS and DTCW ranges provide the vented second barrier. Requirements vary by jurisdiction and by the authority having jurisdiction, so confirm rather than assume: the ranges are not interchangeable and a single-wall unit installed where double-wall is required cannot be signed off.
