Weak current College】 【Central air-conditioning system design pumps.

<br> Summary: the so-called water pump selection calculation is actually estimate (many calculation formula itself is the estimate), estimate the share of detailed some of the more comprehensive consideration is the precise calculation. Includes pump selection index, a simple estimation .method of pump head, frozen pump lift utility estimation, pump lift design, etc. <br> <br> Keywords: pump selection pump lift lift estimate water cooling equipment resistance <br> <br> The so-called water pump selection calculation is .actually estimate (many calculation formula itself is the estimate), estimate the share of detailed some of the more comprehensive consideration is the precise calculation. <br> <br> Special Supplement: when the design flow in device rated flow nearby above resistance can form ., more often than the rated flow of the device. Similarly, water pipes, the water flow rate proposals, look-up table for resistance value. <br> <br> About pump lift is too large. Design selected pump lift is too large ., will make the wealthy head for traffic, traffic increases that makes water pump noise increase. In particular, traffic increases also makes pump motor load increases, the current increase, fever, "countless times bearing" or things that are very likely to burn the .motor. <br> <br> In addition to "pump outlet pressure only 0.22 MPA" describes what? pump export pressure difference is the key to the problem. For example, open system of water pump is placed in 100 m above the top outlet .pressure if this system 0.22MPa will pump on the floor to the top of the 100-metre high, outlet pressure is 0.32MPa! <br> <br> ----- Pump lift-simple estimation method --- <br> .<br> HVAC pump selection: usually choose specific speed ns in 130 to 150 of centrifugal pumps, pump flow rate should be the chiller rated flow 1.1 ~ 1.2 times (a single fetch 1.1, two parallel take 1.2. According to estimates can be broadly .through each 100 m length along loss to 5mH2O, pump lift (mH2O): <br> <br> Hmax = △ P1 + △ P2 +0.05 L (1 + K) <br> <br> △ P1 as chillers evaporator pressure drop. .<br> <br> △ P2 for the ring of the parallel of the air conditioning did not end-device for maximum pressure losses of a pressure drop. <br> <br> L the most negative loop length <br> <br> .K is the most negative loop local resistance equivalent length sum and the ratio of the total length of straight pipe, when most negative loop longer K value when taking 0.2 ~ 0.3, most unfavorable loops shorter when k-value of 0.4 ~ 0.6 <br> .<br> ----- Frozen pump lift utility estimation methods ---- <br> <br> Here are talking about is a closed-type air conditioner cooling systems of resistance, because this system is of common systems. <br .> <br> 1. water chillers resistance: provided by the Unit factory, usually 60 ~ 100kPa. <br> <br> 2. piping resistance: including friction resistance, local resistance, friction resistance per unit length of that group than friction depends .on the technical and economical comparison. If a value greater then the pipe diameter is small, the initial investment in the province, but the energy consumption of pump operation; if the value of small and large, on the contrary. The current design of cold .water pipe than friction group should be controlled at 150 ~ 200Pa / m, diameter is large, the value can be smaller. <br> <br> 3. air conditioning is not end device resistance: Terminal units for types there are fan-coil .units, packaged air conditioners, etc. Their resistance is based on the design of air into and out of the air conditioning coil parameters, cooling capacity, water temperature, from the factory through the coil configurations calculating available, many of the rated operating conditions on .the values in a sample of the product cannot be found. This resistance is generally 20 ~ 50kPa range. <br> <br> 4. regulating valve of resistance: air conditioned room always requires control of room temperature, in air conditioning terminal device of .water on electric regulating valve is two-way room temperature control. 2-way valve specifications by valve fully open when flow capacity and allows to choose a pressure drop. If this allows for the pressure loss value and the control of the valve to a good .performance; if value is small, the control performance is poor. Valve fully open when the pressure loss of the slip road to a percentage of the total pressure drop is called the right of the valve. Water system design requirements valve right degrees S> .0.3, so two-way control valve allows for the pressure loss is generally not less than 40kPa. <br> <br> According to the above, can produce a rough estimate of about 100m high high-rise building air-conditioning system pressure loss ., that is, the circulating pump head: <br> <br> 1. water chillers resistance: 80kPa (8m water column); <br> <br> 2. piping resistance: frozen in the engine room of the strainer, water harvesting ., water separator and pipeline, resistance to 50kPa; for transmission and distribution piping length 300m and side than friction 200Pa / m, the friction resistance for a 300 * 200 = 60000Pa = 60kPa; consider the distribution side of local resistance to the abrasion resistance of .50%, then the local resistance to 30kPa 0.5 = 60kPa *; the total resistance system piping to 50kPa + 60kPa + 30kPa = 140kPa (14m water column); <br> <br> 3. air conditioning terminal device resistance: combined air conditioner .resistance than the fan coil resistance, so take the former resistance to 45kPa (4.5 water column); <br> <br> 4. the second valve of resistance: 40kPa (0.4 water column). <br> <br> 5. Thus ., the water system of the resistance of the parts are: 80kPa + 140kPa + 45kPa + 40kPa = 305kPa (30.5m water column) <br> <br> 6. the pump head: take a safety factor of 10%, then lift h .= 30.5m * 1.1 = 33.55m. <br> <br> According to the above estimates as a result, you can scale the basic master class with building air-conditioning system of the pressure loss value range, and in particular should prevent have .not been calculated, The conservative and the system pressure loss estimation, pump lift selected too large, leading to energy waste. <br> <br> <br> ----- Pump lift design-by-the-<br> < .br> (1) cold and hot water piping systems <br> <br> Open-water system <br> <br> Hp = hf + hd + hm + hs (10-12) <br> <br> Closed water systems .<br> <br> Hp = hf + hd + hm (10-13) <br> <br>-Hf, hd-water system overall frictional resistance and local resistance losses, Pa; <br> <br> Hm-device .resistance losses, Pa; <br> <br> Hs-open-water system for hydrostatic pressure, Pa. <br> <br> Hd / hf value, small residential building in 1 ~ 1.5; large skyscraper in 0.5 ~ 1; long .distance pipeline (central cooling) in 0.2 ~ 0.6. Equipment resistance loss see table 10-5. <br> <br> (2) cooling water pipeline system <br> <br> Cooling water cooling tower 1) <br> <br .> Equipment resistance loss <br> <br> Device name <br> <br> Resistance (kPa) <br> <br> Notes <br> <br> Centrifugal chillers <br> <br> Evaporator <br> <br> .30 ~ 80 <br> <br> According to the different products and <br> <br> Condenser <br> <br> 50 ~ 80 <br> <br> According to the different products and <br> <br> Absorption .chillers <br> <br> Evaporator <br> <br> 40 ~ 100 <br> <br> According to the different products and <br> <br> Condenser <br> <br> 50 ~ 140 <br> <br .> According to the different products and <br> <br> Cooling tower <br> <br> 20 ~ 80 <br> <br> Different spray pressure <br> <br> Cold and hot water coil <br> <br> .20 ~ 50 <br> <br> Flow speed in 0.8 ~ 1.5m / s or so <br> <br> Heat exchanger <br> <br> 20 ~ 50 <br> <br> Fan-coil units <br> .<br> 10 ~ 20 <br> <br> Air blower plate Tube capacity, the greater the resistance, the greater maximum around 30kPa <br> <br> Automatic control valves <br> <br> 30 ~ 50 <br> < .br> Cooling tower cooling water can be calculated according to the following type: <br> <br> W = Q / c (tw1-tw2) kg / s (10-14) <br> <br>-Q - discharge .of thermal cooling towers, kW; compression refrigerating machine, refrigerator load 1.3 times; absorption chillers, go to the refrigerator load of about 2.5; <br> <br> C - - the specific heat of water, kJ / (kg · oC) .c = ambient temperature at 4.1868kJ / (kg · oC); <br> <br> Tw1-tw2-cooling towers and water temperature, oC; compression refrigerating, 4 ~ 5oC; absorption chillers, to 6 ~ 9oC. <br> .<br> 2) pump lift <br> <br> Cooling water pump needed lift <br> <br> Hp = hf + hd + hm + hs + ho <br> <br>-Hf, hd-cooling water pipeline system .overall frictional resistance and local resistance, mH2O; <br> <br> Hm - - condenser resistance, mH2O; <br> <br> Hs-cooling tower water lifting height (from the cooling container pool to the nozzle height difference), mH2O .; <br> <br> Ho-cooling nozzle spray pressure, mH2O, approximately 5mH2O. <br> <br>.