Raypak 302A-902A manual Hydronic Heating, P ft

Failure to exceed 105ºF (41ºC) within 7 minutes may result 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 of the vent system. The bypass allows part of the heater discharge water to be mixed with the cooler heater return water to increase the heater inlet temperature above 105ºF (41ºC). This precautionary measure should prevent the products of combustion from con- densing in most installations. Warranty claims will be denied when condensation occurs.

Cold water operation issues are applicable to both cold water start and cold water run applications. Cold water operation for 7 minutes or less on start-up is acceptable. Where cold water starts will last longer than 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 and thereby raise the inlet temperature to at least 105ºF (41ºC) within the 7-minute time limit.

Cold Water Starts

Frequent (more than once a week) cold water starts, wherein the inlet water temperature remains below 105ºF (41ºC) for more than 7 minutes, must have cold water start protection. Known protection methods con- sist of mixing heated outlet water with the inlet water with a bypass to raise the inlet to 105ºF (41ºC) or high- er. Once the system is heated up and has return water temperatures of 105ºF (41ºC) or higher, the mixing of outlet water with inlet water is no longer needed and the bypass can be shut off. If the bypass is not shut off as the system heats up, the outlet temperature may continue to climb and actuate the high limit, thereby

shutting down the heater. Thus an automatic valve system, such as a three-way proportional valve or a modulating two-way valve to control the bypass, should be utilized.

Cold Water Run

Cold water run differs from cold water start in that the system 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 is kept in a narrow temperature range, a permanent manual bypass can be employed and manually adjust- ed to achieve an inlet temperature of 105ºF (41ºC) or higher. 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 of being able to adjust to changes in the system water coming back to the heater take-off.

Temperature & Pressure Gauge

The temperature and pressure gauge is factory- mounted in the in/out header.

Hydronic Heating

Pump Selection

In order to ensure proper performance of your heater system, you must install a correctly sized pump. Ray- pak recommends using a 20°F ΔT as design ΔT. (ΔT is the temperature difference between the inlet and out- let water when the heater is firing at full rate). If a ΔT of larger than 20°F is necessary, see Table H and Table I for flow rate requirements.

Model		10°F	T	20°F	T	30°F	T	40°F	T	Min. Flow			Max Flow
No.		gpm	P (ft)	gpm	P (ft)	gpm	P (ft)	gpm	P (ft)	gpm	P (ft)	T	gpm	P (ft)	T
302A		50	3.1	25	0.8	N/A	N/A	N/A	N/A	20	0.5	25	90	9.8	6
402A		67	5.5	34	1.4	22	0.6	N/A	N/A	20	0.5	34	90	10.0	7
502A		84	9.1	42	2.3	28	1.1	21	0.6	21	0.6	40	90	10.4	9
652A		N/A	N/A	55	4.1	36	1.8	27	1.1	27	1.1	40	90	10.8	12
752A		N/A	N/A	63	5.7	42	2.6	32	1.5	32	1.5	40	90	11.3	14
902A		N/A	N/A	76	8.3	50	3.8	38	2.2	38	2.2	40	90	11.7	17
Notes:	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 less
		than 20 gpm.

2.Rear-mounted pumps may provide higher flow rates on smaller models than the system requirements.

Table H: Heater Rates of Flow and Pressure Drops

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