Condensing Boiler Control Strategies & System Distribution

Hot water supply temperature reset is a basic control strategy that is very popular and has been utilized for quite some time. This control strategy resets the hot water supply temperature based on a system variable, typically outside air temperature. The ability to reset the hot water supply temperature centers on the principle that the building heating load is proportional to the outside air temperature. So, at a higher outside air temperature less heating is required and can be achieved with a lower-than-design hot water supply temperature. Energy savings is achieved when the outside air temperature increases since a lower hot water supply temperature can maintain comfortable space conditions.

Strategies utilizing pump controls are an alternative that can work in conjunction with hot water reset for additional energy savings.The most common method of pump control for variable speed pumping applications is ΔP pumping that includes a differential pressure transmitter located in the distribution loop. The location of the transmitter is important to ensure a good representation of the hydronic system pressure drop at the remote coil is provided.

A second method of pump control uses a similar process, but evaluates system ΔT as a control signal. Pumps have recently become more adaptive and controllable with the use of a built-in microprocessor that automatically adjusts system flow based on a defi ned condition. Controlling to a defined ΔT is a relatively new concept. It utilizes return and supply water temperature sensors that are connected to the pump and the microprocessor to vary the output based on maintaining a design ΔT between the hot water supply and hot water return piping