Water ring heat pump system variable water volume operation and its related problems

Currently in the field of real estate water ring heat pump air-conditioning system due to its high system efficiency (compared to air-cooled heat pump system), investment and living, easy independent billing and other characteristics of a wide range of applications, but also achieved some economic benefits. However, the system also exposed some problems during use. As part of the load conditions, how to reduce the pump power consumption?

In the real estate project air conditioning system, the current use of sub-district independent household water ring heat pump units, each district (households) use their own needs to determine the opening and closing time and the required temperature. Cooling water system set. Each district (household) charges their respective meters when they are charged, and the electricity charges of centralized pumps and cooling towers are apportioned by each user. This raises the question of how to reduce the pump's power consumption during the transitional season and when only a few users are staying. On this point we will naturally think of the pump to run with variable water. But the problem is that the conventional central air-conditioning system chilled water pump variable range of water is limited by the type of chiller evaporator, usually full liquid evaporator is not less than 70% of rated water, dry evaporator and lithium bromide unit evaporator Less than 50% of rated water. However, for the water ring heat pump system, its partial load may reach 10% or less. How to maintain the economic operation of the water system under such a small load? Water system in the design to take what measures?

First: Each water ring heat pump unit cooling water into the goods are set two-way valve, the switch linkage with the unit, the unit open to open, the unit off it is also closed.

Second: the unit side of the pump open and stop and two-way valve linkage, the system as long as there is a two-way valve is open, the unit side pump put into operation.

Third: the unit side pumps according to the supply and return pressure for frequency control.

Fourth: Pump in the system design process should consider the load characteristics with reasonable size.

Fifth: cooling tower (boiler) side of the pump according to the system back to the temperature decided to open stop. (Above 32 Â° C or below 16 Â° C)

The program in the implementation process mainly to solve two problems. The first is based on the load characteristics of how to configure the unit side of the pump. The second is the system uses what kind of control. In response to these two points we have to elaborate.

1 unit side of the pump configuration

The use of variable speed pump running water system in the choice of pump should pay attention to two points,

First, it is necessary to prevent the vibration frequency of the pump after the speed change from resonating with the natural frequency of the vibration isolation device.

Second, to prevent the water system due to the closure of two-way valve caused by changes in the characteristics of the pipeline, so that the pump operating point into the surge zone. (On this point in the pump selection by the manufacturer to check)

Below we through a project example to illustrate the variable water pump system selection. A real estate project using water ring heat pump air conditioning system, the total cooling water 600t / h, the system may reach the minimum load of 5% of the design load. , Under normal circumstances configure the three pumps, each flow is 200t / h. Assuming the rated speed of the pump are 1450r / min. When the partial load of 5%, if the amount of circulating water decreases, then the pump speed will reach 218r / min (constant pressure pump flow and speed into a relationship). What happens then?

We know a speed of 1450r / min pump vibration frequency is about 24HZ, when the pump speed reduced to 218r / min when the vibration frequency of the pump is about 3.6HZ. The natural frequency of the shock absorber is about 3 ~ 6HZ. This pump will slow down in the process of resonance. Therefore, in order to prevent resonance (also to control the pump vibration transmission rate), and general civil buildings in terms of pump vibration frequency and natural frequency of the shock absorber should be more than 2.5. In this example, it is assumed that the natural frequency of the shock absorber is 6HZ, then the vibration frequency of the pump should be above 15HZ and the minimum speed of the pump should not be less than 900r / min (at this moment, the pump flow is about 120t / h). This speed corresponds to the system at 20% of the partial load. Therefore, in order to ensure that the pump can operate economically even when the system is under a lower load, we have another small pump in the water system design.

Small pump configuration is based on the principle of a large pump running to its minimum speed, if the system load is still further decline, then the big pump down, turn on the small pump. That is, the maximum flow of a small pump for a large pump speed after the minimum flow.

In this case the flow of a small pump should be 120t / h (its rated speed is still 1450r / min). When the speed of 900r / min, the flow rate of about 75t / h, this flow corresponds to about 12.5% â€‹â€‹of the part load. This pump configuration can basically meet the economic operation of the water system. If you need to further reduce the water flow with the load drop, it can also be equipped with a smaller flow pump. The same principle. In this example, the nominal flow of this pump is 75t / h (rated speed 1450r / min). When the speed drops to 900r / min, the pump flow drops to 45t / h, which corresponds to a partial load of 7.5% of the system. This configuration can further reduce the pump at low load power consumption.

2 variable volume control system

Variable water system uses DDC control, the advantages of this control method is (1) the entire system, reliable, energy-saving. (2) cheaper prices, low installation costs, save space. (3) easy to use, easy to upgrade, strong security. (4) Have technical support. (5) Can realize the soft start of the pump, make the startup process have little influence on the power grid.

The entire control system is in each floor or a certain air-conditioning area set a site controller, when a water ring heat pump unit is put into use corresponding to the two-way valve that is open (unit and two-way valve control by the unit itself Supporting controller). Two-way valve account opening signal to the scene controller, and then by the scene controller signal to the central building of the central controller, and finally by the central controller will signal to the pump, control the pump start. When all water ring heat pump units in the system stop working, all two-way valves are closed, no signal is sent to the scene controller at this time, and there is no signal input from the central centralized controller, at this moment, the control water pump is turned off.

After the central controller sends the signal to the pump (group), the pump starts. According to the example above 75t / h flow of small pumps first start. The speed of the pump after start-up by the side of the supply and return water pressure control, with the system put into operation more units, was opened two-way valve also will increase, the system pressure drop for the supply and return gradually reduce the water pump The speed gradually increased. When the speed of the small pump reaches its rated speed, the pressure difference between the supply and return water will decrease if it decreases again. The small water pump stops running. The pump with the flow rate of 120t / h is put into operation. If the open two-way valve in the system continues to increase , The system supply and return water pressure continues to decrease, the pump speed continues to increase, when the pump reaches its rated speed, if the supply and return water pressure drop then the pump stops running, a 200t / h flow pump started . The speed of this pump is still gradually increased by the differential pressure of the supply and return water. When the rated speed is reached, the second 200 t / h pump is put into operation if the differential pressure between supply and return drops again. At this time the first 200t / h flow pump deceleration, the two pumps at the same time by the supply and return water pressure control to maintain synchronous speed. When both pumps reach their rated speed, the third 200 t / h pump continues to operate if the pressure differential continues to drop. At this point the original speed reaches the rated speed of two pumps decelerate, three pumps with the same supply and return water pressure control to maintain synchronous speed until the system reaches full capacity of three pumps have reached the rated speed.

For the cooling tower (boiler) side of the pump its open stop by the unit side of the pump backwater temperature control, fixed water volume operation mode. When the return water temperature exceeds 32 â„ƒ, the pump is turned on and the cooling tower is put into operation. When the backwater temperature is lower than 16 â„ƒ, the water pump is turned on and the boiler is put into operation.

3 variable volume operation economy analysis

After the unit side of the water pump running mode changes in the energy-saving effect of what exactly? We are still based on the previous example to do an engineering analysis.

The real estate project is a comprehensive project, which includes office, shopping malls, residential and other parts. Its annual air-conditioning running time is 250 days. (Ie 6000 hours) throughout the year air-conditioned load distribution in Table 1:

Load rate% 5 10 20 30 40 50
Time frequency h
Load rate% 60 70 80 90 100
Time frequency h 300 50

Several models of pumps rated power respectively: (1) flow 200t / h pump, rated power of 22kw. (2) flow 120t / h pump, rated power of 11kw. (3) Flow 75t / h pump, rated power of 7.5kw. According to the constant pressure system pump flow and input power showed a one-way relationship, we can calculate the variable water pump system at different air conditioning load factor of the input power. See Table II.

Load rate% 5 10 20 30 40 50
Input power kw 4.5 6 11 19.8 27.2 33
Power consumption kwh
Load rate% 60 70 80 90 100
Input power kw 39.6 46.2 52.8 59.4 66
Power Consumption kwh Cumulative 199490

If the project pump is not configured with two other small pumps, only three large pumps for speed control. So in the partial load conditions the annual pump power consumption will happen? See Table III.

Load rate% 5 10 20 30 40 50
Input power kw 13.6 13.6 13.6 19.8 27.2 33
Power consumption kwh
Load rate% 60 70 80 90 100
Input power kw 39.6 46.2 52.8 59.4 66
Power consumption kwh Total 206,300

From the above comparison we can see that the program of variable water volume 1 compared with constant volume of water-saving 49.6%, variable volume program 2 compared with the fixed-volume program savings of 47.9%. From this we can draw the economic significance of the water-saving operation scheme of the water pump in the water ring heat pump air-conditioning system. In addition, the variable-volume program 1 and variable-volume program 2, the power saving effect is not obvious, mainly because in this case the air-conditioning system is not running at low load for a long time. Through this example, we can also draw such experience, low load air conditioning system running time is not long, the variable water system pump configuration can be configured directly to two to three large flow pumps, without the additional configuration of small flow Water pump. This simplifies the control of the water system. Only when the air-conditioning system runs at a low load for a long time, one to two small-flow pumps need to be additionally configured from the perspective of further energy saving.

SDDF QE series pressure filters are designed in accordance with international regulation, which consist of a filter housing with a screw on cover plate.

Standard equipment

-mounting holes in the filter head

-two-piece bowl for size 660 and above

-compatibility with fire-resistant fluids HFA/HFC

-drain plug with pressure relief(size 330 and above)

Connection Diagram

DF QE connection