Sizing a Heat Exchanger Help

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New Member
May 23, 2023
Could you please help me with the sizing of the heat exchanger for the hot water storage tank?

The capacity of the buffer tank is 2000 liters (528.34 gallons). I have made 2 HX in the upper zone, one for DHW and the other for wet UFH using Alpex pipes measuring 26x3mm (1"x0.12 inches) and both with a length of 50m (164.04 ft).

I made the test with a temperature of 40°C (104°F) in the buffer tank at the inlet of the heating circuit, I couldn't get more than 30°C (86°F).
There is also a problem with DHW, sanitary water from the supply is around 15°C (59°F). When I turn on the faucet, it reaches nearly 40°C (104°F) until the supply from the heat exchanger is depleted, and then it drops to around 25°C (77°F).

I made a mistake in my calculations somewhere, a correction is inevitable. But I would like to ask for the help of someone more experienced to determine how big of a heat exchanger I need so that I don't make two of them :)

Consideration can be given to a copper or flexible stainless steel pipe for HX, as well as the installation of a submerged stainless steel boiler tank 80-100L (21-27 gallons) for DHW. What do you recommend?

My climate zone is Dfa/Dfb or 5A (continental humid hot/warm summer). The total area of the house is 150m² (1614.59 sq ft) on 2 floors. The maximum heat losses at an outside temperature of -15°C (5°F) and inside temperature of 22°C (72°F) are 4.5-5 kW/h (15342-17060 BTU/h), and the losses at an average outside temperature of 5°C (41°F) and inside temperature of 22°C (72°F) are around 2.2-2.5 kW/h (7512-8533 BTU/h).

I apologize for listing more units and measures, and I'm from Europe, so we use a different system of units.

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I had no choice, in the end, I had to change the pex-al-pex pipes and replace them with flexible stainless steel pipes of 1" diameter. I installed about 160 ft ( 50m ) of this pipe for HX in the upper zone and will be used for underfloor house heating.
Instead of pex-al-pex DHW tube exchanger, I installed a 22 gal ( 100L ) stainless steel boiler.

I still haven't finished the buffer tank and put it into operation, but as soon as I have new information I will let you know :)

Sizing a Heat Exchanger Help Sizing a Heat Exchanger Help
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