Valves and their benefits

An instructive article related to the Independent Pressure Control Valves and their benefits in the HVAC System.

by Danfoss

In HVAC systems it is important to ensure that all coils in the system can receive the design flow and ensure thermal comfort for the occupants. This thermal sensation has an impact as important as a good design, because it defines the person who wants to return, can work comfortably and efficiently and operating costs are the most optimal (Fig. 1).

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The imbalance is caused naturally by the pressure drop in the pipeline and in the intrinsic elements of the system. For this reason, the manual balance valves are used to guarantee the flow to each coil and the control valves to maintain the temperature of the room. (Fig. 2 and Fig. 3).

 

During the normal operation of the HVAC system there are variables that come into play and influences the way in which the equipment will operate (outside temperature, number of people occupying areas, electrical equipment on, luminaire etc) and for this reason the elements operate at loads partial and this is where the variable speed drives play a crucial role to operate the pumps and fans, supplying the energy required at that time.

Following the idea of ​​the ice water system, the pumps' variators are directly linked to the balancing of the system and its correct operation will be determined by the opening and closing of the control valves.

Following the traditional design of control valves of 2 valves and manual balance valves, typical problems begin to arise, such as overflow in coils causing a low dT in the chiller, low flow in the furthest coils, poor operation of the pumping system and requiring additional pumps to be started unnecessarily. This generates dissatisfaction of the occupants and high energy and maintenance costs. (Fig. 4)

The overflow is an issue that is very important to take care of, because the efficiency of them is reduced and as you can see in the graph (Fig. 5) the dT of the chiller is greatly affected and the operation of the pumps (% flow) becomes a very high cost in energy.

The reason is that the pressure changes are constant and traditional valves are selected taking into account only a pressure drop, having a dynamic system no longer operate optimally.

To avoid this there is a very simple solution and with which we can replace these 2 valves by 1 alone, this is where the Pressure Independent Balance and Control Valves (PIBCV) play a crucial role in the designs and operation of the HVAC system. These valves have the characteristic that in the same body there is a flow limiter, a differential pressure controller and the control is carried out by means of an actuator. (Fig. 6)

The differential pressure control plays the most decisive role in the operation of the PIBCV, this consists of a diaphragm, which with the pressure changes generated with the opening and closing of the valves, keeps a constant flow. This is very helpful for the actuators to operate only due to the temperature variations of the areas and to increase the service life of the areas. (operation cycles are reduced).

Following the trends of the market and the internet of things, there are currently control elements (actuators that allow us to have communication to the BMS in a constant way allowing us to have monitored the position in which the valve is located, what is the flow rate is supplying, injection temperature and return of the coil, consumption, etc. (Fig. 7)

Not only will it allow us to have all the information at the moment and be able to make decisions in a timely manner, it also allows us to reduce installation and configuration costs. Because the valve flow adjustment can be made through the BMS. It will not be necessary to do it in the commissioning and it will greatly reduce installation costs, make changes during the operation without having to access the roof.

In conclusion, in any system where variable speed pumps are going to be used, the best option will always be to install Pressure Independent Balance and Control Valves because their selection is simple, the equipment will operate according to the required demand, help to make efficient the dT of the chillers, improve the operation of the pumps and reduce the operating costs during the useful life.

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