Weak current College】 【modular air-source heat pump water flow control technology.

Modular air-source heat pump unit is the individual independence of air-cooled heat pump units grouped together using, modular unit is the commercial air conditioning market sales very good models. It has the advantage that can load circumstances change module unit of quantity or allow the customer to use another unit, the convenience of our customers according to their own funds and use of flexible procurement and use of the unit. In modular air-source heat pump unit of structure, each module has the same caliber of inlet and outlet, modules can simply pipe butt, the installation is easy, since the module machine this special form of module unit of inlet and outlet flow velocities are unsure to module unit control a certain degree of difficulty. Make sure that each module is suitable for water flow is module unit can work necessary to ensure that no appropriate water flow may cause a module unit evaporator ice, condensing pressure is high, the compressor cylinder "bite". For module unit General cooling capacity, in the event of the failure, the brand's reputation will be very large. So the module unit water flow control and protection is very important, appropriate water testing methods and testing parts can guarantee the unit only in system water is greater than the minimum allowable work under water, to a large extent can avoid air-conditioning host fails.

First, the module unit connection pipe design

1.1 module units within the main water pipe layout design

Module unit for pooled between various modules into the outlet, when the connection between the various modules, module-main number is relatively small, the main water pipe can be used with programs layout; if the module number best use with programs layout, so you can ensure that each of the flow between modules.

1.2 module units within the main water pipe water flow control

Module unit in all modules share between the inlet and outlet pipe diameter depends not only on each module cooling capacity size also depends on the entire module is biggest module unit. Usually the main water pipe module velocity control in 0.5 ~ 4m/s within the more appropriate. Because if the velocity is relatively large, the water pipe between modules frictional resistance is large, easily between the various modules of distribution, right of the main water pipe velocity can be ignored in the main water pipe producing pressure drop. If a module of the heat exchanger in the rated flow of the pressure drop for 30kPa, module internal main water pipe pressure drop in 2kPa, each module between water flow almost the same, but if the module internal plumbing of pressure drop over 5kPa, module unit between the water flow deviation may exceed 10 per cent. For heat exchangers in the rated flow of the pressure drop, the greater the need to set the internal pressure of the main water pipe allows larger, the delivery lift of pump.

1.3 module unit system water filter selection and installation

Module unit for pipe diameter is generally relatively large, from the project cost on pipe materials not normally choose to corrosion of copper pipe and other materials, often choose seamless as water pipes in General. The whole water pipes with pipes electric welded connections, the welding process produces a large number of welding slag if not valid. Welding slag once inside the heat exchanger against very large, will likely heat exchanger partially blocked. If the unit heat exchanger using brazing or heat exchanger tube heat exchanger will be very difficult to remove, because both of these heat exchangers are not mechanical cleaning, if you use shell and tube heat exchanger will easier removal of welding slag. If you are unable to effectively clear the heat exchanger of welding slag will cause the water side of local water heat exchanger, at which time the refrigerant side refrigerant flow base maintained, might lead the water temperature has dropped below the freezing point of water even, because the water side of traffic jam down cause adjacent of refrigerant side appears incomplete evaporation, back to the trachea or even freeze Frost, easily is densener. If the heat exchanger local jam light degree of a system's entire water flow without too much change, current protection switch has no effect. And antifreeze protection sensor (inserted into the heat exchanger for internal testing water temperature) are not detected by the lowest temperature, anti-freezing protection and cannot work, terrible thing happened-the heat exchanger Frost until the entire refrigeration system for scrap. In order to prevent the welding slag and other impurities clogging heat exchanger except during construction construction specifications, manufacturers of chillers design process can prevent this from happening.

Water filter is module unit common parts, is the water system is the most critical one of two parts. Select the appropriate water filters can effectively prevent water pipe construction process of impurities into the heat exchanger. Proper water filter mesh size and the form is very critical and should be reserved for the by-pass unit installed into the pipe valve, after the installation is complete before commissioning bypass module unit heat exchangers for water pipes cleaning. At this point in the inlet water filter it is best to use the 100 mesh stainless steel stamping filter, to the end of a water filter mesh size should be larger than 100 mesh (temporary use, open the debugging after bypass valve). If the system has an alternate pump when open main standby pump, the pipes of the maximum flow rate, open 24 hours after cleaning filter. This can be almost all large particle impurities accumulate in water filter, and then replace the water filter to 60 end up debugging.

1.4 module unit selection of plumbing materials

Usually in module unit of water pipeline system host factory used galvanized seamless pipe, pipe in engineering construction site cannot implement zinc plating, forever pipe easy rust corrosion. If the use of corrosion-resistant steel lined with plastic, there would be no pipeline corrosion and welding welding slag produced a large number of blocked pipes, while increasing the installed cost, but greatly reduce air-conditioning unit of repair and maintenance costs, in the life of the integrated costs will be significantly reduced.

2. module unit water detection method

2.1 module unit water flow detection

In module unit control on each module now requires a water flow signal, and only one of the main module needs to flow signal, these two methods in the module unit production plant are used. Each module has a flow signal flow control methodTo compare the true reflection of the module's current situation; if only the main module add flow signal does not really reflect the current per module, for a production plant in terms of such an approach can reduce costs, but for each module, this control method is not ideal.

As a module for water testing is currently mainly two kinds of simple and practical, cost-effective form of detection, target-type flow switches, a pressure differential and flow switches, the following comparison of the two test methods of installing and using properties.

2.2 target-type flow switch installation and use

Target-type flow switch is installed on the target movie, water pipe in pipe flow in water impact target flow sheet of bending deformation, thereby driving the micro switch output control signal to module unit controller advised flow can start unit. Because module unit main water pipe flow velocity in change (increase or decrease in the number of end use), to the target-type flow switch installation to a certain degree of difficulty. Typically target flow plate installation has three conditions: first, it is not an action, the second is stuck in the tube upside not reply, the third is normal. Installation is very good and the pipe diameter and Installer experience very relevant, pipe diameter larger target-type flow switch once installed, the higher the accuracy rate.

Typically target stream tablets not action because the target stream movie installed depth, need to swing or replace the target stream. Many installation workers encounter this situation if you cannot quickly resolve often shorted flow switch or adjust adjusting screw making a module unit loses water protection.

If you are stuck in the pipe not reply often target stream movie is too wide for the sake of the first action is to be stuck in the upper part of the pipe (the situation in small diameter pipes in cold for more), this is to install the provider cannot be found, flow switch also lost its role. If the installation space not enough even if you can work, as the pipes rusty or scaling and so the actual use of smaller diameter, is also possible to make the water flow switch card within the pipe cannot be effective action.

Because module unit in variable number of modules on site, the main water pipe velocity cannot be determined, to the target stream switch installation caused great difficulty, the main water pipe velocity change target type flow switch frequently swing movement reduction; when water mixed with air, the water of air shocks caused by target stream tablets, target flow velocity tablets instantly reset to unit error flow information (to prevent this error usually unit controller delayed processing flow information). At the same target-type flow switch target flow in normal use is prolonged water pressure, easy bending deformation fatigue, especially in the velocity over 3m/s and above their life will be shortened considerably.

If each module needs to flow signal, it is not suitable to install target-type flow switch. Currently, each module Eagle module machine heat exchanger nearest pick module unit main water pipe, it is not possible to provide the installation target flow switch needed before and after the period of a minimum distance of straight pipe, some manufacturers have to give up each module requires a current signal this ideal flow protection method.

2.3 differential pressure flow switch installation and use

Differential pressure flow switch is based on the resistance of the HVAC equipment and flow curve design. We know that the HVAC equipment, heat exchangers, water filters, water pumps and valves, and other devices has its resistance and flow characteristic curve, by testing it at both ends of the poor and out of the water and the device preset values, you can precisely control flow.

Pressure-and target-type flow switch than it is a precise flow control, it has precise flow control value. It can be installed directly in the unit or in a field installation. If the installation of the unit from the pressure differential switch connect two copper tube-heat exchangers and export, import and export of measuring the differential pressure, which is reflected in the flow. But the user does not need to be installed on-site and wiring, which avoids the target-type flow switch installation not accurate result set failed. If installed in a site can use dual set point adjustable pressure differential switch, master from the module into the outlet pipe leads to? 6.35 copper tubes tube nut received pressure differential switch. If the field has a Portable Ultrasonic Flowmeter to measure primary pipe flow better, you can adjust the pressure differential switch for adjusting screw set you need to protect the flow values, if the field does not have this condition, you can also match factory provided by the module combination of main inlet and outlet flow and pressure difference curve, set to the appropriate pressure difference to achieve precise control flow.

While the pressure differential switch another field to adjust the set point can be used as a module unit pressure differential is too large (i.e. module unit internal scaling or jam). Specific method is in normal water flow, adjust the pressure differential switch on the set-point adjustment screws make their closed or the output of the power indication light is on, then slow-in so that the pressure differential switch is off or output led off after 1 ~ 2 laps. That is, if the module unit into the outlet pipe and heat exchanger between the pressure difference is greater than the set value will be issued the alarm message prompts the user to clean the heat exchanger and pipeline.

Differential pressure flow switch with flow control and accurate, the system is no longer the extra resistance, also on the pipe diameter is not required and no flow disturbance interference, and other characteristics, you can replace any form of target-type flow switch as HVAC water system of flow control, relative to the target-type flow switch it to avoid pump cavitation induced false flow (actual velocity is very big, but the water mixed with air and the actual flow rate is not significant), and therefore can be widely used brazed plate heat exchangers, a tube heat exchanger and shell and tube heat exchanger modular air-source heat pump water flow control and also some antifreeze protection features.

3. differential pressure flow switch application in module unit

3.1 water protection and blocking instructions

Use for module machine brazing, heat exchanger tube heat exchanger or shell and tube heat exchanger the pressure differential and flow curve may vary if each module machines use a fixed set-point pressure differential switch that can be tested at the factory to ensure that the configuration of the pressure differential switch protection flow value is appropriate. Recommend disconnecting the flow is greater than the rated flow of 50 per cent reduction in traffic buildingAnd that is less than 80% of the rated flow.

If the module unit only the primary module receives flow signal, you can use adjustable double set-point pressure differential switch. According to the module unit of inlet and outlet pressure drop and flow curve adjustment pressure set value, another set points can be used as a heat exchanger clogged or scaling of indication, on the specific installation location reference chart.

3.2 pressure differential bypass control

In module unit of water systems, usually module unit side water system using fixed water system can guarantee the stability of the module unit operation, the Terminal side water system with variable water system can reduce energy consumption and water pumps for the end of the cold quantity shift between the end of the beginning of a moderate reduction in equipment investment and lower operating costs is very favourable.

In order to meet the module unit side of water control and end side of varying water control, usually uses the pressure differential bypass control method, i.e. the end side of the water changes (i.e. load changes due to end of line capacity and actual load) caused by the pressure difference in charge of road or with change. According to the pump performance curve, if guaranteed main water pipe for back pressure difference, also ensures that the pump flow, likewise the water flow into the unit does not change.

Double set point pressure differential switch can be applied to water system control variable for the return pipe pressure difference between that when poor water pressure for back over the pressure differential switch high limit set point, the pressure differential switch output of high limit and C-closed NO so that the floating point control of electric by-pass valve door opening action to reduce the implementation for the return pipe pressure difference between; as for the return pipe pressure difference between lower than the pressure differential switch lower limit set point, the pressure differential switch lower limit output NO C-closed, and the floating point control of electric by-pass valve performs shutdown actions. As for the return pipe pressure difference between between the pressure differential switch high limit and lower limit set point, the floating point control of electric by-pass valve not action to maintain a constant flow rate to maintain a constant differential pressure. Double set point pressure differential switch can be a floating point pressure differential bypass controller, by adjusting the pressure differential switch height limit set points, you can resize a floating belt, much better than previous pressure controller switch quantity control method.

IV. concluding remarks

In module unit each module uses the pressure differential switch or a main module using the pressure differential switch, are very good results, especially in the modules have been added or deleted from the main water pipe velocity change and water pipes have a small amount of air pressure differential switch work very stable, not appear similar to the floating target flow switches, after repeated testing action and reset flow all have clear flow of value, than the target stream more exceptional performance.