With an Integrated Combo System, the hot water temperature is approx. 130˚F (54˚C) which is 60˚F (15.5˚C) above the return air temperature. These units typically have a temperature rise of 35˚F (2˚C) to 40˚F (4˚C) and therefore would deliver air at the diffuser at approximately 105˚F (40.5˚C) to 110˚F (43˚C).
Design vs. Field Conditions
The factors discussed above become very important to consumer comfort. Even small differences between design parameters and actual field conditions can impact greatly on output capacity. Therefore, it is important to do a thorough and complete commissioning of the integrated combo system to ensure the design parameters are met.
Water System Pressures
Within the water system of an Integrated Combo system, there are three terms that the designer/installer must understand. These are head pressure, water flow rate, and pressure drop.
Head Pressure
Head pressure is the pressure created by the circulation pump to push water through the piping system. It is this pressure which is used to overcome the resistance to water flow (friction) caused by the water pipe and fittings. It is similar in concept to the external static pressure in an air duct system. Head pressure is measured in feet or water (millimeters of water).
Note: Although the water in the combo system is pressurized by the domestic water system the pump is required to create water flow in the heating loop. The domestic water system applies the same pressure to the supply and return sides of heating loop.
Note: The vertical height of the heating loop does not impact on the head pressure as the pressure required to push the water up the vertical height is offset by the weight of the water in the vertical drop on the other side of the heating loop.
Flow Rate
Flow rate is the amount of water flowing in the system. It is directly related to the head pressure and the resistance to flow. Flow rate is measured in gallons per minute (liters per minute).
Pressure Drop (PD)
Pressure drop (PD) is the reduction in total pressure caused by components added to a piping system such as coils, valves, and fittings. The measurement of pressure drop is the difference in pressure on the inlet side of the component and the outlet side. Pressure drop is measured in feet of water (millimeters of water).
When connecting the water lines for heating loop (air handler) to the domestic water system, the pipes should be connected with a “tee” to the side of a vertical domestic water pipe or the bottom of a horizontal domestic water pipe. This is to help prevent air from entering the heating loop. The connections should be as near as practical to the water heater.
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