How To Select Heat Pump For Water Heating in A School？

The Heat Pump Hot WaterUnit uses the  reverse Carnot cycle principle to make the working fluid undergo a phase change through the movement of the compressor. Using this repeated cycle phase change process, it absorbs heat from the outside (air, water, etc.) and releases it to the cold water. Then the cold water is gradually heated, and the hot water is sent to the user through the water circulation system. PHNIX Heat Pump Water Heaters are widely used in hotels, factories, schools, hospitals, entertainment and leisure, villas, etc. Here, in this article, the method for the selection of a heat pump water heating system for a school will be introduced..

A. Description of the system's maximum daily water consumption and water tank selection

1.  Application: Student shower hot water, toilet hot water, dishes washing hot water, school kitchen hot water. (Specific requirements vary from school to school))

2.  Water Amount Calculation: Student shower hot water (average value): 35L/person*day (the average value is calculated according to the simultaneous using of all student)

3. Shower hot water in bathroom: 5L/person*day (hot water in bathroom sink) . dish washing and kitchen hot water : 10L/person*day (calculated according to 2 meals per day)

Remarks: Hot water resources are precious, and the design of hot water amount is only enough for students to bathe, wash their faces, dishes and also kitchen vegetable washing. Hot water for washing clothes, mops are not included. Schools should raise students' awareness of water conservation.

(Heat pump water heating system for Southwest Jiaotong University In China)

B. Examples

Xinzhan Town Central School in Southwest China:

1.  Water tank calculation

Background information of The School: The school has a total of 922 students and 144 students live in the school dormitory. The school requires sanitary hot water for students to shower, wash their faces, wash dishes in the canteen, and vegetables washing in the kitchen. Taking into account the school's planning, development and system standardization, the number of people for meals is expected to be 1,000 people, and the number of people for shower and face washing is expected to be 200 people. The specific method of the amount of water consumption are shown in the following table:

2. Heat Pump Selections

Considering the water demand, local climate conditions and the capacity changes of the heat pump water heaters under the different local climate conditions, the total amount of domestic sanitary hot water required by the project is up to 20 metric tons. In winter, the lowest ambient temperature is 5℃, and the temperature of tap water is about 10℃. Then the heat required to heat up 20 metric tons of tap water from 10°C to 55°C is calculated with the formula below as:

Q=CMâ–³T=1.163*1(ton)*(55-10)=52KWH

Then the heat required by the heat pump to heat 20T water is: Q=20*52=1040KWH

According to the principles and characteristics of air source heat pumps, the lower the outdoor temperature, the lower the heat output. Therefore, when selecting the heat pump, the heat output of the heat pump should be corrected according to different ambient temperatures. Taking into account that when the ambient temperature is low, the capacity is reduced. At this time, the heating capacity of 1 unit of PHNIX PASHW050S-XI is 12KW, and the heating capacity of 2 units of PHNXI PASHW100S-XI is 24KW. The required working time is:

N=1040/60=17h

According to the above calculation, it is designed to use one unit of PHNIX PASHW050S-XI plus 2 units of PHNIX PASHW100S-XI.