HOMETechnical DataDisrtict cooling & heating
The pump lift is 24 m, Flow is 400 LPM, Pressure loss of heat exchanger is 0.3 bar, Pressure loss of the differential pressure flow control valve is 0.3 bar, and The set differential pressure is operating as the differential pressure between points A and F (2-0.9=1.1 bar); This is a case where a flow of 100 LPM has been distributed to each standing line. If the flow is cut off due to the operation of temperature control valves installed at points B, C, D, and E according to changes in outside temperature, the lift of point A rises, resulting in higher pressure. The differential pressure flow control valve detects the increased lift of point A and increases point F to the same level, thereby maintaining a differential pressure of 1.1 bar between points A and F. The pressure gradient of the entire pipeline becomes constant (refer to Diagram 2), resulting in optimal flow alancing effects despite the variable flow. Also, a constant differential pressure is maintained at all times even in cases where only one or two apartment units require heating, thereby preventing the breakdown of the temperature control valve for each household and completely resolving noise-related problems within households.
In Diagrams 4 and 5, a constant flow control valve (automatic balancing valve) is installed in the same location. If the flow becomes smaller after operation of temperature control valves at points B, C, D, and E, the constant flow control valve will operate below the control range since the flow will be smaller than the original flow of 400 LPM. As such, the pressure gradient within the pipeline will change, leading to a flow imbalance. There will be excessive flow in certain sections. This is why some adopt the solution of installing a constant flow control valve for each standing line, but this leads to the issue of imbalance among households within each standing line. This is why it is recommended that a constant flow control valve should be installed for each household. However, in case of continuous heating, where the pump needs to be operated even when the level of used flow is extremely low, the lift of the circulation pump rapidly increases. As such, there is noise since the differential pressure goes up when the constant flow control valve is operated. Moreover, rapid fluctuations in differential pressure lead to decreased control performance of each household’s temperature control valve and even cause breakdown. This is why there is a need to install a differential pressure valve or differential pressure flow control valve and appropriately maintain a differential pressure of the supply and return to ensure definite balancing effects.
As shown in Diagram 7, the method of balancing the flow with only a differential pressure valve of the machinery room is adopted for small systems, and is mostly used for single pump systems that do not have a high circulating head. The capacity is 80% or more of the pump flow. The set differential pressure is the same as the pump lift, or as the pressure loss value of the overall circulation pipelines if there is an overall pressure loss value.
A system that uses only a differential pressure valve is difficult to apply when several pumps are operated or load fluctuations are substantial.
In this case, there is a need to install a differential pressure valve for pump relief purposes and set up a differential pressure flow control valve for each apartment building. This would enable to establish balance among apartment buildings as well as among different zones within an apartment building through a differential pressure flow control valve.
< Valve selection >
(1) Differential pressure valve
As a relief purpose, it determines the relief flow which is over 25 % of a pump flow since it could be selected within the scope where the pump would not get excessive loads. The set differential pressure would be the same as the pump lift or the pressure loss value of the overall circulation pipelines.
e.g.) Pump flow Qp=75ton/h
Pump lift H=24m=2.4bar
Relief flow (usually, 30~35% of pump flow) Qr=22.5T/H
Select the valve Cv value as YDF-1F 40A(Cv=18) which is over 16.95
(2) Differential pressure flow control valve
Since the valve controls the flow changes occurring due to the temperature control valve operation within an apartment, if the flow of each apartment would be 25ton/h,
Q = 25ton/h(417LPM)
(△P : Here, 0.3. It is the maximum pressure loss of the valve itself and constant)
Select the valve Cv value as YDF-2F 65A(Cv=58) which is larger than 53.2. At this time, the controlling differential pressure DPs such as the points A-A', B-B', and C-C' which the differential pressure flow control valve should control are irrelevant to the valve size selection and are different a bit according to working places. When the required flow for each apartment is very huge, the differential pressure flow control valve should be enlarged. So, if the range ability would be 1/40, 1/40 of the maximum flow could not be controlled, in this case, it would be appropriate to install the differential pressure flow control valve for each zone like Picture 7.