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1.Simple estimation method for pump head
Selection of HVAC water pumps: usually using specific speednsIn130～150The centrifugal clean water pump should have a flow rate equal to the rated flow rate of the chiller unit1.1～1.2Multiple (single unit taken)1.1Two parallel connected devices1.2According to estimation, we can roughly take each100The loss along the length of the meter pipe is5mH2OPump head（mH2O）：
Hmax=△P1+△P2+0.05L (1+K)
△P1Reduce the water pressure of the evaporator in the chiller unit.
△P2The water pressure drop of the unit with the highest water pressure loss at the end of each air conditioner connected in parallel in the loop.
LFor the pipe length of the most unfavorable loop
KTo calculate the ratio of the total equivalent length of local resistance in the unfavorable loop to the total length of the straight pipe, when the unfavorable loop is relatively longKValue taking0.2~0.3， The unfavorable loop is relatively shortKValue taking0.4～0.6
2.Practical estimation method for head of chilled water pump
What is being discussed here is the resistance composition of a closed air conditioning cold water system, as this system is a commonly used system.
1.Resistance of chiller unit: provided by the unit manufacturer, generally60~100kPa.
2.Pipeline resistance: including frictional resistance and local resistance, where the frictional resistance per unit length, i.e. the specific friction group, depends on technical and economic comparisons. If the value is large, the pipe diameter will be small, saving initial investment, but the energy consumption of the water pump operation will be high; If the value is small, then the opposite is true. At present, the specific friction group of the cold water pipeline in the design should be controlled within150~200Pa/mWithin the range, when the pipe diameter is larger, the value can be smaller.
3.Resistance of air conditioning terminal devices: The types of terminal devices include fan coil units, modular air conditioners, etc. Their resistance is provided by the manufacturer through coil configuration calculations based on the parameters, cooling capacity, water temperature difference, etc. of the air inlet and outlet air conditioning coils proposed in the design. Many rated operating conditions can be found on product samples. This resistance is generally within20~50kPaWithin the scope.
4.Resistance of regulating valve: Air conditioned rooms always require temperature control, and setting an electric two-way regulating valve on the water circuit of the air conditioning terminal device is a means of achieving temperature control. The specifications of a two-way valve are selected based on the flow capacity and allowable pressure drop when the valve is fully opened. If the allowable pressure drop value is large, the control performance of the valve is good; If the value is small, the control performance is poor. The percentage of pressure drop when the valve is fully open to the total pressure drop of the branch is called valve weight. Valve weight is required in water system designS>0.3Therefore, the allowable pressure drop of the two-way regulating valve is generally not less than40kPa.
Based on the above, a rough estimate of a building can be made100mThe pressure loss of the air conditioning water system in high-rise buildings, i.e. the required head of the circulating water pump:
1.Resistance of chiller unit: take80 kPa（8mWater column);
2.Pipeline resistance: Take the resistance of the dirt remover, water collector, water separator, and pipelines in the refrigeration room as50 kPaTake the length of the pipeline on the transmission and distribution side300mCompared to frictional resistance200Pa/mThe frictional resistance is300*200=60000 Pa=60 kPaIf considering the local resistance on the transmission and distribution side as frictional resistance50%, then the local resistance is60 kPa*0.5=30 kPaThe total resistance of the system pipeline is50 kPa+60 kPa+30 kPa=140 kPa（14mWater column);
3.Resistance of air conditioning terminal device: The resistance of modular air conditioners is generally greater than that of fan coil units, so the resistance of the former is taken as45 kPa（4.5Water column);
4.Resistance of two-way regulating valve: take40 kPa（4.0Water column).
5.So, the sum of the resistance of each part of the water system is:80 kPa+140 kPa+45 kPa+40 kPa=305 kPa（30.5mWater column)
6.Pump head: take10%The safety factor, then the headH=30.5m*1.1=33.55m.
Based on the above estimation results, it is possible to have a basic understanding of the range of pressure loss values for air conditioning water systems in buildings of similar scale. In particular, it is important to prevent overestimation of system pressure loss and excessive selection of pump head due to lack of calculation and conservatism, which can lead to energy waste.
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