Optional Accessories

Frost Control Application/Operation

Cold climates, in combination with higher indoor humidity levels, may cause frost to form on the plate heat exchanger. To protect against the formation of frost, a temperature sensor is installed to measure the temperature of the air leaving the plates in the exhaust airstream. There are three different methods of frost control that may optionally be used. These options are installed, wired and pre-set at the factory. To identify specific components, see the included unit-specific schematic wiring diagram.

1.Timed Exhaust frost control

The supply blower cycles on and off based on a factory provided and installed timer. The timer is located on the right hand side (low voltage side) of the control module.

2.Plate heat exchanger bypass – Open/Closed When the exhaust air leaving the exchanger (cube) drops below the adjustable set-point, both the face and bypass dampers will allow air to bypass the cube. This allows warm exhaust air to melt any frost on the cube. Once the exhaust air temperature rises above the set-point, the unit returns to normal operation.

3.Electric preheat frost control

An electric preheater can optionally be built into the outdoor air intake. When the temperature of the exhaust air leaving the plate unit (the cube) drops below the adjustable set-point, the preheater will switch on. Once the exhaust air temperature increases, the preheater will switch off.

Frost Threshold Temperatures

Indoor RH @ 70°F	Frost Threshold Temp

20%	-5º F

30%	-5º F

40%	-5º F

The typical temperature setting corresponds to the indoor air relative humidity as shown in the Frost Threshold Temperatures table and represents when frost can occur. An increase in pressure drop would indicate that frost is occurring. Both the pressure sensor and the outdoor air temperature sensor must trigger in order to initiate frost control. The two sensors together insure that frost control is only initiated during a real frost condition. Field wiring of a light (or other alarm) between 6 & C in the control center will notify personnel when unit is in frost control mode (refer to Remote Panel Wiring schematics for wiring details). The following explains the three options in more detail.

Timed exhaust frost control includes a timer in addition to the thermostat and pressure sensor. The timer is located on the right hand side of the control module (low voltage side). When timed exhaust frost control is initiated, the timer will turn the supply blower on and off to allow the warm exhaust air

to defrost the cube. Default factory settings are 5 minutes off and 30 minutes on.

Plate (cube) bypass. The plate bypass frost control function is essentially the same as Economizer mode (see below) except that it is initiated by temperature sensors for the purpose of frost removal or prevention.

Electric preheat frost control includes an electric heater at the outdoor air intake, an airflow pressure switch and a temperature sensor. See also Electric Heater Application / Operation. When electric preheat frost control is initiated, the electric preheater will turn on and warm the incoming air to prevent frost accumulation on the cube.

Economizer Application/Operation

Under certain conditions, the most efficient use of the PVe Heat Recovery Ventilator includes bypassing the incoming outdoor air around the plate heat exchanger. When cooling air is being called for and the outdoor air temperature is below a pre-set point, the PVe will switch to Economizer Mode. Integral face and bypass dampers will cycle into a bypass condition, allowing incoming cool air to flow past the cube, rather than flow through it. Economizer Mode is strictly temperature initiated and dependent on the Temperature Sensor with override located in the control center. See component #7 on the Typical Control Center Components illustration.

Model PVe Heat Recovery Unit 11