Onix Installation Manual.qxd - Affordable Home Inspections

Injection Pump SizingInjection systems incorporate a seriesof sensors, some on the control pipingto measure fluid temperatures, whileother sensors are located outside tomeasure outside air temperature. Withthis information the injection control isable to calculate the actual heat loadand required water temperature at anygiven time.Why is this important? Non-electricalmix valves are set to provide a fixedtemperature all the time. This temperatureis set to handle the heating loadon the coldest day of the year. Thistemperature is only reached for a smallpercentage of the time. For the rest ofthe heating season, a mix valve is providingtemperatures that will be higherthan required for the heat load at mosttimes.Reset systems are continuously optimizingthe heating system by modulatingthe supply temperature. This helpsreduce the possibility of potential thermalswings associated with mild falland spring days.Injection pumps are sized the sameway zone pumps are sized.Pure Water:BTU/h = gpm × 500 × ∆T50% Glycol-50% Water:BTU/h = gpm × 455 × ∆TAs a rule, an injection pump will besized for a smaller flow rate than thecombined secondary zones.Each zone is designed around a 20¡F∆T. This is done for comfort andAppendixresponse of the heating system. Theinjection pump, on the other hand, isonly responsible for transferringBTUs. This can be done with a higher∆T value. As the ∆T increases, theresulting gpm rate will decrease whilestill providing the same BTU delivery.For example, assume a zone supplytemperature of 120¡F, a zone returntemperature of 100¡F and a boiler supplytemperature of 180¡F. The zoneflow rate is 10 gpm. What size doesthe injection pump need to be?The system load can be figured usingthe equation for water:BTUs = 10 × 500 × 20 = 100,000Zone PumpsPrimary Pump/Boiler LoopInjection PumpBalancing ValveSwing Check ValveZone Return LinesSupply From BoilerReturn To BoilerWatts Radiant: Onix Installation Manual page 73