Calculation of the area for domestic hot water heat exchangers
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I would like to ask the experts: how is the heat exchange area of the heat exchangers in a domestic hot water unit calculated? The following conditions are given: 1. Heat source: steam, with a pressure of 0.4 MPa. 2. Each unit contains two heat exchangers, each capable of producing at least 20 m3/h of hot water. 3. The outlet temperature of the hot water is 60 degrees Celsius. 4. The unit can withstand a pressure of 1.6 MPa. 5. The pressure drop should not exceed 10 KPa. 6. Each unit is equipped with a hot water tank with a capacity of 1 cubic meter. 7. Each unit has a digital thermostatic mixing valve installed. I would appreciate any guidance on this matter. Is there also a schematic diagram of a domestic hot water unit that I could use as a reference? I’m a beginner and not very familiar with this topic; thank you in advance to all the experts.
This is water mixed with steam to become hot water, and there is no need to calculate the heat exchange area.
Don’t all heat exchangers for regular domestic hot water require the calculation of the heat exchange area?
Let’s do the heat balance calculation. The enthalpy of steam at 0.4 Mpa is 2740, the enthalpy of water at 60°C is 251, and the enthalpy of water at room temperature (20°C) is 83.9. The density of water at 60°C is 983.2. Therefore, 983.2*20*251 = a*2740 + (983.2*20 – a)*83.9, which gives a = 1237. For cold water: 18427
What is the value calculated for the 4th floor?
The original poster isn’t clear in their explanation; they seem to be referring to both heat exchange units and the method of directly heating steam in a cold water tank (referred to as a steam heater). With a steam heater, calculations are based on heat balance, while for heat exchange units, it’s necessary to calculate the heat exchange area. Since the products available vary from one manufacturer to another, the results also differ.
Thank you, maybe I didn’t explain myself clearly.
The requirements specified by the poster are very clear; it is a typical heat exchanger (non-volume type heat exchanger) + thermal storage tank-based heat exchange unit, and attention should be paid to the issue of scaling on the secondary side of the heat exchanger.