Carrier GT-PX Split Series Installation, Operation & Maintenance Instructions Manual

R e s i d e n t i a l S p l i t - 6 0 H z R 2 2 & R 4 1 0 AR e v. : 5 J u n e , 2 0 0 814 W a t e r- S o u r c e H e a t i n g a n d C o o l i n g S y s t e m sGround-Water Heat Pump Applications -“Indoor” Compressor Section OnlyOpen Loop - Ground Water Systems(“Indoor” Compressor Section Only)The “outdoor” version of the compressor section may notbe used with open loop systems due to potential freezing ofwater piping. Typical open loop piping is shown in Figure 9.Shut off valves should be included for ease of servicing. Boilerdrains or other valves should be “tee’d” into the lines to allowacid flushing of the heat exchanger. Shut off valves shouldbe positioned to allow flow through the coax via the boilerdrains without allowing flow into the piping system. P/T plugsshould be used so that pressure drop and temperature can bemeasured. Piping materials should be limited to copper or PVCSCH80. Note: Due to the pressure and temperature extremes,PVC SCH40 is not recommended.Water quantity should be plentiful and of good quality.Consult Table 3 for water quality guidelines. The unit canbe ordered with either a copper or cupro-nickel waterheat exchanger. Consult Table 3 for recommendations.Copper is recommended for closed loop systems and openloop ground water systems that are not high in mineralcontent or corrosiveness. In conditions anticipating heavyscale formation or in brackish water, a cupro-nickel heatexchanger is recommended. In ground water situationswhere scaling could be heavy or where biological growthsuch as iron bacteria will be present, an open loop systemis not recommended. Heat exchanger coils may over timelose heat exchange capabilities due to build up of mineraldeposits. Heat exchangers must only be serviced by aqualified technician, as acid and special pumping equipmentis required. Desuperheater coils can likewise become scaledand possibly plugged. In areas with extremely hard water,the owner should be informed that the heat exchangermay require occasional acid flushing. In some cases, thedesuperheater option should not be recommended due tohard water conditions and additional maintenance required.Water Quality StandardsTable 3 should be consulted for water quality requirements.Scaling potential should be assessed using the pH/Calciumhardness method. If the pH <7.5 and the Calcium hardnessis less than 100 ppm, scaling potential is low. If this methodyields numbers out of range of those listed, the RyznarStability and Langelier Saturation indecies should becalculated. Use the appropriate scaling surface temperaturefor the application, 150°F [66°C] for direct use (well water/open loop) and DHW (desuperheater); 90°F [32°F] forindirect use. A monitoring plan should be implemented inthese probable scaling situations. Other water quality issuessuch as iron fouling, corrosion prevention and erosion andclogging should be referenced in Table 3.Expansion Tank and PumpUse a closed, bladder-type expansion tank to minimizemineral formation due to air exposure. The expansion tankshould be sized to provide at least one minute continuousrun time of the pump using its drawdown capacity rating toprevent pump short cycling. Discharge water from the unitis not contaminated in any manner and can be disposedof in various ways, depending on local building codes (e.g.recharge well, storm sewer, drain field, adjacent streamor pond, etc.). Most local codes forbid the use of sanitarysewer for disposal. Consult your local building and zoningdepartment to assure compliance in your area.The pump should be sized to handle the home’s domesticwater load (typically 5-9 gpm [23-41 l/m]) plus the flow raterequired for the heat pump. Pump sizing and expansiontank must be chosen as complimentary items. For example,an expansion tank that is too small can causing prematurepump failure due to short cycling. Variable speed pumpingapplications should be considered for the inherent energysavings and smaller expansion tank requirements.Water Control ValveNote the placement of the water control valve in figure 9.Always maintain water pressure in the heat exchanger byplacing the water control valve(s) on the discharge lineto prevent mineral precipitation during the off-cycle. Pilotoperated slow closing valves are recommended to reducewater hammer. If water hammer persists, a mini-expansiontank can be mounted on the piping to help absorb theexcess hammer shock. Insure that the total ‘VA’ draw of thevalve can be supplied by the unit transformer. For instance,a slow closing valve can draw up to 35VA. This can overloadsmaller 40 or 50 VA transformers depending on the othercontrols in the circuit. A typical pilot operated solenoid valvedraws approximately 15VA (see Figure 24). Note the specialwiring diagrams for slow closing valves (Figures 25 & 26).Flow RegulationFlow regulation can be accomplished by two methods. Onemethod of flow regulation involves simply adjusting the ballvalve or water control valve on the discharge line. Measurethe pressure drop through the unit heat exchanger, anddetermine flow rate from Tables 11a through 11b. Sincethe pressure is constantly varying, two pressure gaugesmay be needed. Adjust the valve until the desired flow of1.5 to 2 gpm per ton [2.0 to 2.6 l/m per kW] is achieved. Asecond method of flow control requires a flow control devicemounted on the outlet of the water control valve. The deviceis typically a brass fitting with an orifice of rubber or plasticmaterial that is designed to allow a specified flow rate. Onoccasion, flow control devices may produce velocity noisethat can be reduced by applying some back pressure fromthe ball valve located on the discharge line. Slightly closingthe valve will spread the pressure drop over both devices,lessening the velocity noise. NOTE: When EWT is below50°F [10°C], a minimum of 2 gpm per ton (2.6 l/m per kW)is required.