Central air conditioning water system design knowledge

1. Open system
The water system is directly connected to the big gas. Commonly used in cooling water system, the system is relatively simple.
When the water pool capacity is larger, the water temperature is more constant, and it has a certain cooling storage capacity in summer.

High oxygen content in the water, more opportunities for corrosion of piping and equipment.
Need to increase the extra energy to overcome hydrostatic pressure, the pump power will increase. Hydraulic balance is relatively difficult.
 

2. Closed system
Water piping system is not directly connected to the atmosphere; pump selection is relatively small compared to open (static pressure) pump head, power are relatively small.
Piping and equipment corrosion opportunities; system design is relatively simple;
To have an expansion tank (fixed-pressure effect), the height should be higher than the highest point of the water system more than 1.5m; to have a bleeder valve and other valves.

3. Same program and different program water system
(1) the same program water system: supply and return water through each loop of equal length of the pipeline; mainly to ensure that the resistance of the piping system is roughly the same, the distribution of water flow uniformity; the need to set up the return pipe, the length of the pipeline is long, the initial investment is slightly higher.
(2) heterogeneous program water system: supply and return water through each loop of the pipeline length is not equal
Do not need to return pipe, pipeline short, simple pipeline, low investment; may lead to uneven distribution of water and liquid volume phenomenon; can be installed in the branch pipe flow regulator; it is recommended that the installation of balancing valve.

4. Hot and cold water piping
(1) two-control water system: heat, cooling combined with the same piping system. Suitable for winter, summer cold, heat load is clear, the transition season is very short or the transition season does not require air-conditioned buildings.
Cooling in summer, heating in winter, the transition season can be used natural cooling source (such as fresh air) cooling building.
Piping system is simple, initial investment; can not meet the requirements of cooling and heating at the same time.
(2) Three-control water system: cold and hot water supply pipes are connected to the end equipment at the same time (the coil is still cold and hot), each end equipment can be independently cooled or heated, cooled, heated return water piping shared.
Can meet the requirements of cooling and heating at the same time, the piping is relatively simple.
In both cooling and heating end equipment running at the same time, the water temperature of the return pipe is a mixture of chilled water and hot water return temperature, this water temperature will be higher than the normal requirements of the chiller return temperature and lower than the normal operation of the heat exchanger return temperature. There is a heat and cold loss, equipment energy consumption will be much larger than when the two are running independently.(3) Four-control water system: separately set up cooling and heating pipelines, but the pipelines for cooling and heating return water are shared.
The end must have both cold and heat coils; can flexibly realize the simultaneous supply of cold and heat, there is no heat and cold loss; piping system is complex, high initial investment, occupying much space in the building; generally used in special high-standard buildings (eg: five-star hotels).

5. Fixed water flow
Fixed water flow: in the fixed water system, there is no automatic water control measures. Generally used to adjust the end of the air volume or electric three-way valve to implement temperature self-control regulation; through automatic control of the three-way valve opening, adjust the bypass branch and the DC branch of the water flow, so as to control the amount of water through the end of the equipment.
The system is simple, easy to operate, without the need for complex self-control equipment.
The total capacity of the chiller unit and the total flow of the pump must be calculated according to the sum of the maximum value of the cooling capacity of each end and cannot be decided according to the maximum value of the sum of the cooling capacity of each end hour by hour, or else it will be insufficient due to the lack of flow and result in the insufficiency of some of the cooling capacity of the end.