Summary of key points of air conditioning water system design

When the pipe diameter is between DN100 and DN250, the recommended flow velocity is about 1.5m/s. When the pipe diameter is less than DN100, the recommended flow velocity should be less than 1.0m/s. When the pipe diameter is greater than DN250, the flow velocity can be increased. The calculation should pay attention to the correspondence between the pipe diameter and the recommended flow rate. Air conditioning repair

The current size specifications of pipe diameters are: DN15, DN20, DN25, DN32, DN40, DN50, DN70, DN80, DN100, DN125, DN150, DN200, DN250, DN300, DN350, DN400, DN450, DN500, DN600

Note: Generally, when selecting a water pump, the inlet and outlet pipe diameter of the water pump should be one model smaller than the pipe diameter of the pipe section where the water pump is located. For example: the pipe diameter of the pipe section where the water pump is located is DN125, then the inlet and outlet pipe diameter of the selected water pump should be DN100. Shanghai Central Air Conditioning Project

Heating water flow speed/(m/s)

Design experience value of household water machine

 The pipe velocity is calculated at 1.8 m/s, and the flow calculation formula is: pipe cross-sectional area × 1.8 × 3600 (converted to h)

2. Installation of fittings of air-conditioning water system

1 The design position of the pump in the system. Shanghai air conditioning design

Generally speaking, the chilled water pump should be located at the front end of the chiller, and the chilled water coming back from the end will be pumped back to the chiller through the chiller pump; the cooling water pump is located on the water path where the cooling water enters the unit, and the cooling water from the cooling tower is pumped back through the cooling water pump. Unit: The hot water circulation pump is located on the return water main pipe, and the hot water returned from the end is pumped back to the plate heat exchanger through the hot water circulation pump.

2 Valve design on the cooling tower.

1) Solenoid valve is added to the water inlet pipe of the cooling tower (manual valve is not recommended).

2) The pipe drain valve should be installed indoors (if it is placed outdoors, because there is some water in the pipe, it is easy to freeze in winter).

3 Water quality treatment

1) Water filter: Regardless of the open or closed system, the water filter must be considered in the system design. At present, the commonly used water filter devices include metal mesh, Y-type pipe filters, straight-through decontamination devices, and so on. Generally installed on the inlet pipes of chillers, water pumps, heat exchangers, electric control valves and other equipment

2) Closed water system: softened water treatment equipment and corresponding water supplement system must be installed in the cold and hot water system.

The installation position of the electronic water treatment instrument: placed behind the water pump and in front of the host.

4 Valves before and after the water pump

1) The inlet pipe of the water pump is connected in sequence: butterfly valve-pressure gauge-soft connection.

2) The outlet pipe of the water pump is connected in sequence: soft connection-pressure gauge-check valve-butterfly valve.

    5 sub-catchment

 For air-conditioning water systems with more than two channels of supply, water collectors should be installed. The diameter of the collector and manifold should be initially selected according to the cross-sectional velocity (0.5~1.0m/s) when the total flow passes through, and should be greater than 2 times the diameter of the larger opening of the pipe; the diameter of the sub-cylinder, the manifold and the collector is D The determination:

1) Determine the D sub-cylinder according to the cross-sectional flow rate. The calculation is based on the cross-sectional flow rate of 8-12m/s; the water separator and the water collector are calculated based on the cross-sectional flow rate of 0.1m/s.

2) Determine D according to empirical formula estimation, D=(1.5~3)×D MAX, D MAX is the larger diameter of the branch pipe.

3) Add an electric pressure difference bypass valve and a bypass pipe between the manifolds (the pipe diameter is generally DN50).

4) A thermometer should be installed on the return pipe of the water collector.

6 Location of various instruments

Arrange temperature gauges, pressure gauges and other measuring instruments in a place that is convenient for observation. The valve height is generally 1.2 ~ 1.5m above the ground. When it is higher than this height, a working platform should be installed.

1) Pressure gauges: pressure gauges should be installed on the pipes outside the water chiller, water inlet and outlet pipes, water pump inlets and outlets, and the branch valves of the water collectors and distributors;

2) Thermometer: Thermometers should be installed on the inlet and outlet pipes of the water chiller and heat exchanger, on the water collector and manifold, after the branch valves of the water collector, and the water supply and return branch pipes of the fresh air unit.

7 Discharge and exhaust of water system

1) At the lower point of the water system, drain pipes and drain valves should be installed, and the drain time is 2 to 3 hours.

2) At the higher points of the water system, a gas collecting tank should be designed, and a venting device should be installed at each higher point (when laying without a slope, at the end of the horizontal pipe flow).

8 Selection of differential pressure bypass valve

In the variable water volume water system, in order to ensure a constant flow of cold water flowing through the evaporator in the chiller, a bypass pipe is installed on the water supply and return mains of multiple chillers. A bypass regulating valve for differential pressure control is installed on the bypass pipe. The larger design flow is determined by the cold water volume of a chiller, and the pipe diameter is directly selected according to the larger allowable flow rate of the cold water pipe.

9 Unit location

The distance between the protruding parts of the two compressors is less than 1.0m, the distance between the refrigerator and the wall and the distance between the non-main passages is not less than 0.8m, and the distance between large and medium-sized refrigeration units (centrifugal, screw, absorption chiller) is 1.5 ~2.0m. The upper part of the refrigeration machine room of the refrigeration unit is preferably reserved for lifting hooks or electric lifting equipment for lifting larger parts.

Three steps for selecting water pumps for air conditioning water systems

The first step is to determine the flow rate of the pump

1 Cooling water flow rate.

It is generally selected according to the values provided by the product samples, or calculated according to the following formula, where Q is the cooling capacity of the refrigerating host.