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NZERTF Changes in Operational Strategy

Changes in Operational Strategy
  • Dehumidification within the NZERTF during the first year of operation was supplemented by the air-to-air heat pump using its dedicated dehumidification mode. The heat pump switches to its dedicated dehumidification mode when the desired dry bulb temperature (thermostat setting) is met but the house humidity, as measured by a wall-mounted humidistat, is above its set point. For this dedicated mode, the heat pump operates in the cooling mode but adds heat to the supply air by means of a downstream hot gas reheat coil. The unit dehumidifies without decreasing the home's dry bulb temperature. The efficiency of the heat pump when operating in its dedicated dehumidification mode is considerably lower than its normal cooling mode efficiency. During the second year of operation, (October 2014 – September 2015), the heat pump's dehumidification mode will be disabled; instead supplemental dehumidification will be provided by a whole house dehumidifier. The whole house dehumidifier only operates when the heat pump is not running and the wall-mounted humidistat is not satisfied. Air is drawn from the living room and supplied to the whole house dehumidifier in the basement. The dehumidified air is subsequently delivered to the same supply duct used by the heat pump to distribute air to the entire house. This change in operating strategy will enable a direct comparison of the energy requirements needed to dehumidify the house using the two different approaches.
  • During the first year of operation the lowest fan speed on the heat recovery ventilator (HRV) was selected to supply outdoor air at a rate that exceeded by approximately 25 % the required minimum in ASHRAE Standard 62.2-2010 "Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings". During the second year of operation, the airflow rate and the HRV operating schedule were adjusted such that the HRV will provide almost the exact amount specified according to ASHRAE Standard 62.2-2010.
  • The control logic within the thermostat used to control the two speed air-to-air heat pump and auxiliary heat was found to be less than optimal. A replacement thermostat was installed with control logic more suitable to the NZERTF.
  • The supplemental resistive heat unit was significantly oversized for the NZERTF. It was replaced with a resistive heat unit more appropriately sized.
Created December 3, 2014, Updated August 25, 2016