Estimation of HVAC cooling capacity, pump head, ventilation
DATE:2024-10-15 11:08:16
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The cooling capacity of air conditioners for home use is directly related to the room area, sealing conditions, the number of people, the degree of sunlight exposure and other factors.
Before purchasing an air conditioner, it is best to choose a suitable model and power reasonably according to the size of the room area and air circulation.
Mainly for villas, large rooms or office use, you can press:
Ordinary environment: one cubic meter of required cooling capacity: 50W.
Harsh environment: one cubic meter required cooling capacity: 70W
Estimation method 1:
HVAC water pump selection: usually selected than the number of revolutions ns in 130 ~ 150 centrifugal submersible pumps, pump flow should be 1.1 ~ 1.2 times the rated flow rate of the chiller (single take 1.1, two parallel take 1.2. By estimation can be roughly taken per 100 meters of pipe length along the loss of 5mH2O, the pump head (mH2O):
Hmax=△P1+△P2+0.05L(1+K)
△P1 is the water pressure drop of the evaporator of the chiller.
△P2 is the water pressure drop of the one that accounts for the largest water pressure loss of the air-conditioning end unit in parallel in this loop.
L is the pipe length of the most unfavorable loop
K for the most unfavorable loop in the sum of local resistance equivalent length and the total length of the straight pipe ratio, when the most unfavorable loop longer K value of 0.2 ~ 0.3, the most unfavorable loop shorter K value of 0.4 ~ 0.6
Estimation method 2:
What is talked about here is the resistance composition of closed air conditioning chilled water system, because this kind of system is the most commonly used system.
1. chiller resistance: provided by the unit manufacturer, generally 60 ~ 100kPa.
2. Piping resistance: including friction resistance, local resistance, which unit length of the friction resistance that is more than resistance depends on the technical and economic comparison. If the value of the pipe diameter is small, the initial investment in the province, but the pump running energy consumption; if the value of small is vice versa. The current design of cold water piping than Mo group should be controlled in the range of 150 ~ 200Pa / m, larger diameter, the value can be smaller.
3. Air conditioning resistance of the device: the end of the type of device has a fan coil unit, combined air conditioner, etc.. Their resistance is based on the design of the air into and out of the air-conditioning coil parameters, cold, water temperature difference, etc. by the manufacturer after the coil configuration calculations to provide many rated value in the product samples can be found. This resistance is generally in the range of 20~50kPa.
4. The resistance of the control valve: air-conditioned rooms are always required to control the room temperature, through the air-conditioning end of the device on the water circuit to set the electric two-way control valve is to achieve a means of room temperature control. The specifications of the two-way valve by the valve is fully open when the flow capacity and the allowable pressure drop to choose. If the value of this allowable pressure drop is large, the valve control performance is good; if the value is small, the control performance is poor. The valve is fully open when the pressure drop of the branch circuit of the total pressure drop of the percentage is known as the valve right degree. Water system design requires valve weight S> 0.3, so the allowable pressure drop of the two-way control valve is generally not less than 40kPa.
According to the above, you can roughly estimate the pressure loss of a high-rise building air-conditioning water system of about 100m high, that is, the head of the circulating water pump required:
1. Chiller resistance: take 80kPa (8m water column);
2. Piping resistance: take the chiller room decontaminator, water collector, distributor and piping resistance of 50kPa; take the transmission and distribution side of the pipeline length of 300m and than the friction resistance 200Pa / m, then the friction resistance of 300 * 200 = 60,000Pa = 60kPa; such as the consideration of the transmission and distribution side of the local resistance for the 50% of the friction resistance, then the local resistance of 60kPa * 0.5 = 30kPa; the total resistance of the system pipeline is 50kPa+60kPa+30kPa=140kPa (14m water column);
3. Air conditioning end device resistance: combined air conditioner resistance is generally larger than the fan coiler resistance, so take the former resistance of 45kPa (4.5 water column);
4. two-way control valve resistance: take 40kPa (4m water column).
5. Thus, the sum of the resistance of the parts of the water system: 80kPa +140kPa + 45kPa + 40kPa = 305kPa (30.5m water column)
6. Pump head: take 10% safety factor, the head H = 30.5m * 1.1 = 33.55m.
According to the above estimated results, you can basically grasp the same size building air-conditioning water system pressure loss value range, in particular, should be prevented because of the lack of calculation, too conservative, and the system pressure loss is estimated to be too large, the pump head selected too large, resulting in energy waste.
1. The calculation of the platform level, station hall level, the main equipment room can be given as an example, and then the screen door air leakage and other important parameters to make specific instructions, so that you can have a preliminary understanding of the design parameters of the subway station.
Unit area heat index: residential: 150W/square; office building: 180W/square; restaurant: 250W/square; subway station no specific indicators, need to be calculated
2. Ventilation and air conditioning of the main equipment estimates:
Ventilation and air conditioning can estimate the main equipment for the host, cooling water pumps, chilled water pumps and cooling towers, air conditioners because it involves heat and humidity conversion, there is no obvious estimation of the data relationship. Generally commonly used Hao Chen or Red Leaf software calculations.
Host cold - chilled water flow - cooling water flow rate relationship is as follows:
Chilled water flow = host cold * 4.187 / (temperature difference) * 3.6 (in m3 / h)
Cooling water flow = chilled water flow * 1.25 (in m3 / h)
Cooling tower flow = cooling water flow * 1.1 ~ 1.25 conventionally speaking, the cooling tower selection of large conducive to heat transfer
Example: host cooling capacity of 1290KW, according to the estimated chilled water flow rate of 222m3 / h, cooling water flow rate of 277m3 / h, the cooling tower flow rate of 300m3 / h. Design drawings parameters.
Back
Before purchasing an air conditioner, it is best to choose a suitable model and power reasonably according to the size of the room area and air circulation.
Mainly for villas, large rooms or office use, you can press:
Ordinary environment: one cubic meter of required cooling capacity: 50W.
Harsh environment: one cubic meter required cooling capacity: 70W
Estimation method 1:
HVAC water pump selection: usually selected than the number of revolutions ns in 130 ~ 150 centrifugal submersible pumps, pump flow should be 1.1 ~ 1.2 times the rated flow rate of the chiller (single take 1.1, two parallel take 1.2. By estimation can be roughly taken per 100 meters of pipe length along the loss of 5mH2O, the pump head (mH2O):
Hmax=△P1+△P2+0.05L(1+K)
△P1 is the water pressure drop of the evaporator of the chiller.
△P2 is the water pressure drop of the one that accounts for the largest water pressure loss of the air-conditioning end unit in parallel in this loop.
L is the pipe length of the most unfavorable loop
K for the most unfavorable loop in the sum of local resistance equivalent length and the total length of the straight pipe ratio, when the most unfavorable loop longer K value of 0.2 ~ 0.3, the most unfavorable loop shorter K value of 0.4 ~ 0.6
Estimation method 2:
What is talked about here is the resistance composition of closed air conditioning chilled water system, because this kind of system is the most commonly used system.
1. chiller resistance: provided by the unit manufacturer, generally 60 ~ 100kPa.
2. Piping resistance: including friction resistance, local resistance, which unit length of the friction resistance that is more than resistance depends on the technical and economic comparison. If the value of the pipe diameter is small, the initial investment in the province, but the pump running energy consumption; if the value of small is vice versa. The current design of cold water piping than Mo group should be controlled in the range of 150 ~ 200Pa / m, larger diameter, the value can be smaller.
3. Air conditioning resistance of the device: the end of the type of device has a fan coil unit, combined air conditioner, etc.. Their resistance is based on the design of the air into and out of the air-conditioning coil parameters, cold, water temperature difference, etc. by the manufacturer after the coil configuration calculations to provide many rated value in the product samples can be found. This resistance is generally in the range of 20~50kPa.
4. The resistance of the control valve: air-conditioned rooms are always required to control the room temperature, through the air-conditioning end of the device on the water circuit to set the electric two-way control valve is to achieve a means of room temperature control. The specifications of the two-way valve by the valve is fully open when the flow capacity and the allowable pressure drop to choose. If the value of this allowable pressure drop is large, the valve control performance is good; if the value is small, the control performance is poor. The valve is fully open when the pressure drop of the branch circuit of the total pressure drop of the percentage is known as the valve right degree. Water system design requires valve weight S> 0.3, so the allowable pressure drop of the two-way control valve is generally not less than 40kPa.
According to the above, you can roughly estimate the pressure loss of a high-rise building air-conditioning water system of about 100m high, that is, the head of the circulating water pump required:
1. Chiller resistance: take 80kPa (8m water column);
2. Piping resistance: take the chiller room decontaminator, water collector, distributor and piping resistance of 50kPa; take the transmission and distribution side of the pipeline length of 300m and than the friction resistance 200Pa / m, then the friction resistance of 300 * 200 = 60,000Pa = 60kPa; such as the consideration of the transmission and distribution side of the local resistance for the 50% of the friction resistance, then the local resistance of 60kPa * 0.5 = 30kPa; the total resistance of the system pipeline is 50kPa+60kPa+30kPa=140kPa (14m water column);
3. Air conditioning end device resistance: combined air conditioner resistance is generally larger than the fan coiler resistance, so take the former resistance of 45kPa (4.5 water column);
4. two-way control valve resistance: take 40kPa (4m water column).
5. Thus, the sum of the resistance of the parts of the water system: 80kPa +140kPa + 45kPa + 40kPa = 305kPa (30.5m water column)
6. Pump head: take 10% safety factor, the head H = 30.5m * 1.1 = 33.55m.
According to the above estimated results, you can basically grasp the same size building air-conditioning water system pressure loss value range, in particular, should be prevented because of the lack of calculation, too conservative, and the system pressure loss is estimated to be too large, the pump head selected too large, resulting in energy waste.
1. The calculation of the platform level, station hall level, the main equipment room can be given as an example, and then the screen door air leakage and other important parameters to make specific instructions, so that you can have a preliminary understanding of the design parameters of the subway station.
Unit area heat index: residential: 150W/square; office building: 180W/square; restaurant: 250W/square; subway station no specific indicators, need to be calculated
2. Ventilation and air conditioning of the main equipment estimates:
Ventilation and air conditioning can estimate the main equipment for the host, cooling water pumps, chilled water pumps and cooling towers, air conditioners because it involves heat and humidity conversion, there is no obvious estimation of the data relationship. Generally commonly used Hao Chen or Red Leaf software calculations.
Host cold - chilled water flow - cooling water flow rate relationship is as follows:
Chilled water flow = host cold * 4.187 / (temperature difference) * 3.6 (in m3 / h)
Cooling water flow = chilled water flow * 1.25 (in m3 / h)
Cooling tower flow = cooling water flow * 1.1 ~ 1.25 conventionally speaking, the cooling tower selection of large conducive to heat transfer
Example: host cooling capacity of 1290KW, according to the estimated chilled water flow rate of 222m3 / h, cooling water flow rate of 277m3 / h, the cooling tower flow rate of 300m3 / h. Design drawings parameters.