Variable flow distribution In heating plants with radiators, the presetting of the thermostatic valve usually takes into account the pressure difference ΔHo = 10 kPa. In the balancing process, the balancing valve STAD in the branch is set to obtain the correct total flow on the branch. This will confirm the default value, and the center of the branch can reach the expected 10kPa. If the differential pressure on the thermostatic valve can exceed 30 kPa, noise may build up in the unit, especially if some air remains in the water. In this case, it is best to use an STAP as shown in Figure 7 to stabilize the pressure drop. On each branch or small riser, a STAP can stabilize the pressure drop. The flow qs can be measured by the measuring valve STAM. Constant flow distribution in residential buildings, water temperature is adjusted by the central controller based on outdoor conditions. Stimulating the pump head may be high (relative to the thermostatic valve too high), it will cause noise. If the backwater temperature is not limited, you can use constant flow distribution. One solution is to arrange a bypass pipe AB and a counterbalance valve STAD-1 for each house (Figure 8a). This balance valve takes away the resulting ΔH. Each house also has a secondary pump with a suitable pump head (less than 30kPa). When the thermostatic valve is closed, Δp applied to the thermostat valve is maintained at an acceptable level to avoid creating noise in the system. The designed secondary flow must be slightly less than one flow to avoid backflow in bypass AB, creating a mixing point at A and lowering the water supply temperature. This is why the balance valve STAD-2 is installed on the secondary circuit. To avoid the use of a secondary pump and STAD-2, a Proportional Pressure Relief Valve, BPV, can be provided per house as shown in Figure 8b. The BPV is connected to the balance valve STAD-1 to obtain the required primary flow rate. BPV set point to choose to meet the requirements. When the thermostatic valve is closed, the pressure differential between A and B increases and tends to exceed the BPV setpoint. With BPV open, the pressure differential between A and B is kept constant. General Design Recommendations The design of a circulatory system depends on its specific characteristics and working conditions. For example, in the design phase of variable flow distribution system, we should consider whether the outage or the same procedure. Constant speed pump or variable speed pump. End device is the regulation control or switch control. Some general recommendations are valid in all cases: 1. The system must be hydraulically balanced under design conditions so that installed power can be delivered. From this point of view, there is no difference between the end device using the adjustment mode or the switch mode control. 2. The compensation method or "TA balance" must be used to optimize the balance process. This avoids the entire system back and forth repeatedly detected, thus greatly reducing labor costs. With both methods, it is possible to clearly identify if the pump size is large and modify the pump, thus reducing pumping costs. The balance program offers the possibility of detecting most of the irregular cycle points. Manual balancing valves are always capable of measuring flow for diagnostic purposes. 3. Care must be taken to adjust the correct characteristics of the two-way control valve (mostly EQ% or EQM). Correct dimensions: The control valve must be able to withstand most of the available circuit pressure differential under design conditions at full open and design flow rates. Control valve valve authority should not fall below 0.25. 4. If the last condition above can not be met in some circuits, install a local Δp controller in these circuits to increase the valve authority of the control valve and reduce the risk of noise. 5. When using a variable speed pump, the Δp sensor must be placed in the correct position to reduce pumping costs and reduce the Δp variation across the control valve to achieve the best compromise between the two. Using computer simulation means that it's easy to find the best sensor location. Conclusion A HVAC system is designed for a certain maximum load. If the system is not fully loaded due to system imbalances under design conditions, the total investment in the entire plant will not be rewarded. When the maximum load is required, the control valve fully opens and can not handle this condition. It is very difficult to determine the size of the two-way control valve. The calculated valve is generally not available on the market, so the size is usually larger. This balance of the circulating system becomes critical, and in general this part of the investment is less than one percent of the total investment in HVAC. Every morning, after a night of shutdown, you need to mobilize all the power to restore comfort as soon as possible. A well-balanced system can do it quickly. If the start-up time can save 30 minutes, compared to 8 hours of work time, you can save 6% of energy consumption per day. This is more than all dispensing pump costs. In variable flow distribution, pump power consumption generally accounts for less than 5% of the seasonal consumption of refrigeration units. The cost of lowering the room temperature by one degree is 10 to 16%. Therefore, getting the right comfort is the best way to save energy. Therefore, all measures must be taken to reduce pumping energy consumption so that they do not adversely affect the operation of the end-device control circuit. Pumping costs can be reduced by maximizing the design water temperature difference, T, and variable speed pumps using the best-positioned Δp sensor. Under moderate load, stable regulation of PI control (Figure 1a) is less than the flow required for switching control, thus reducing pumping costs as well. But the most important thing is to compensate for the pump size is too large. Counterbalance valves that are set with the compensation method show this oversized condition. It can be seen that all overpressures are located on the balance valve near the pump. After correcting the pump, the balancing valve can be reopened. Circulating balance requires the right tools, the latest programs and effective measuring devices. The manual balancing valve is clearly the most reliable and simplest product to get the correct flow under design conditions and always measures the flow for diagnostic purposes. If necessary, can also be connected with the pressure controller.