Raypak Hi Delta 302A-902A Installation And Operating Instructions Manual

16Failure to exceed 105ºF (41ºC) within 7 minutes mayresult in the premature failure of the hot surface ignit-er, remote flame sensor, burners and heat exchanger.It can cause operational problems, bad combustion,sooting, flue gas spillage and reduced service life ofthe vent system. The bypass allows part of the heaterdischarge water to be mixed with the cooler heaterreturn water to increase the heater inlet temperatureabove 105ºF (41ºC). This precautionary measureshould prevent the products of combustion from con-densing in most installations. Warranty claims will bedenied when condensation occurs.Cold water operation issues are applicable to bothcold water start and cold water run applications. Coldwater operation for 7 minutes or less on start-up isacceptable. Where cold water starts will last longerthan 7 minutes or where cold water operation is con-tinuous, provisions must be made to mix higher tem-perature outlet water with the colder inlet water andthereby raise the inlet temperature to at least 105ºF(41ºC) within the 7-minute time limit.Cold Water StartsFrequent (more than once a week) cold water starts,wherein the inlet water temperature remains below105ºF (41ºC) for more than 7 minutes, must have coldwater start protection. Known protection methods con-sist of mixing heated outlet water with the inlet waterwith a bypass to raise the inlet to 105ºF (41ºC) or high-er. Once the system is heated up and has return watertemperatures of 105ºF (41ºC) or higher, the mixing ofoutlet water with inlet water is no longer needed andthe bypass can be shut off. If the bypass is not shut offas the system heats up, the outlet temperature maycontinue to climb and actuate the high limit, therebyshutting down the heater. Thus an automatic valvesystem, such as a three-way proportional valve or amodulating two-way valve to control the bypass,should be utilized.Cold Water RunCold water run differs from cold water start in that thesystem water entering the heater remains below 105ºF(41ºC) continuously. Typically, this is the case in swim-ming pool heating and water source heat pump appli-cations as well as some others. If the system water iskept in a narrow temperature range, a permanentmanual bypass can be employed and manually adjust-ed to achieve an inlet temperature of 105ºF (41ºC) orhigher. An injector pump arrangement may also be uti-lized to keep the heater loop at or above 105ºF (41ºC).An injector pump approach has the added value ofbeing able to adjust to changes in the system watercoming back to the heater take-off.Temperature & Pressure GaugeThe temperature and pressure gauge is factory-mounted in the in/out header.Hydronic HeatingPump SelectionIn order to ensure proper performance of your heatersystem, you must install a correctly sized pump. Ray-pak recommends using a 20°F ΔT as design ΔT. (ΔT isthe temperature difference between the inlet and out-let water when the heater is firing at full rate). If a ΔTof larger than 20°F is necessary, see Table H andTable I for flow rate requirements.Table H: Heater Rates of Flow and Pressure Drops10°F T 20°F T 30°F T 40°F T Min. Flow Max FlowModelNo. gpm P (ft) gpm P (ft) gpm P (ft) gpm P (ft) gpm P (ft) T gpm P (ft) T302A 50 3.1 25 0.8 N/A N/A N/A N/A 20 0.5 25 90 9.8 6402A 67 5.5 34 1.4 22 0.6 N/A N/A 20 0.5 34 90 10.0 7502A 84 9.1 42 2.3 28 1.1 21 0.6 21 0.6 40 90 10.4 9652A N/A N/A 55 4.1 36 1.8 27 1.1 27 1.1 40 90 10.8 12752A N/A N/A 63 5.7 42 2.6 32 1.5 32 1.5 40 90 11.3 14902A N/A N/A 76 8.3 50 3.8 38 2.2 38 2.2 40 90 11.7 17Notes: 1. Basis for minimum flow is 20 gpm or 40°F ΔT. Basis for maximum flow is 90 gpm. Flow switch will not operate if flow is lessthan 20 gpm.2. Rear-mounted pumps may provide higher flow rates on smaller models than the system requirements.