Opportunity:
Using the HyperStat DCV damper signal to control the supply air fan speed on an ERV can be a highly efficient and cost-effective solution for maintaining indoor air quality.
This solution also provides an opportunity for increased energy savings and occupant comfort.
What is an ERV?
Energy Recovery Ventilation (ERV) systems are designed to exchange stale indoor air with fresh outdoor air while recovering energy from the exhaust air.
What is a VFD?
Variable Frequency Drive (VFD) is a type of AC motor drive system that controls motor speed and torque by varying the frequency of the input voltage to the motor, VFDs are commonly used to regulate the speed of the supply and exhaust fan motors in an ERV system.
What is DCV?
Demand-Controlled Ventilation (DCV) not to be confused with direct current voltage is a system used to regulate the amount of fresh air brought into a building’s ventilation system based on occupancy or other factors.
Use Case:
Imagine a single-zone office space with varying occupancy throughout the day. The goal is to ensure excellent indoor air quality while minimizing energy costs. The building is equipped with an ERV system that exchanges the indoor air with fresh outdoor air to maintain indoor air quality (IAQ). The problem here is the supply fan on the ERV is capable of modulating but runs at a constant speed when enabled.
Solution:
Using a HyperStat we can enable and configure any of the three analog outputs for DCV damper control. The 0-10vdc signal from the configured analog output is used as input to the supply fan speed controller or VFD. The DCV damper output signal will modulate when the CO2 level of the zone rises above the CO2 threshold that has been set in the configuration. Using the DCV damper signal from the HyperStat will only work if the supply fan speed controller or VFD can accept an external analog signal for motor speed control. If connecting to a VFD please reference the manufacturer documentation for setting up the min/max motor speed.
Mapping and Configuration :
The first thing we want to do is confirm the fan speed controller or VFD can accept an external analog reference signal. Next, we want to configure any of the three analog outputs for DCV damper control. We’ll need to set a few parameters such as analogOutxAtMinDCVDamper (adj) used to drive the Min Fan Speed, analogOutxAtMaxDCVDamper (adj) used to drive the Max Fan Speed, CO2 Damper Opening Rate (adj) in this case Fan Speed Modulation Rate. CO2 Threshold (adj) CO2 Target (adj).
How does it work?
Controlling the supply fan on an Energy Recovery Ventilator (ERV) using the HyperStat DCV damper signal is simple, here’s how it works:
The onboard CO2 sensor on the HyperStat detects CO2 levels in the space above the threshold indicating a need for more fresh air proportionally increasing the fan speed to analogOutxAtMaxDCVDamper = (Max Fan Speed).
When CO2 levels are at or below the threshold the fan runs at the analogOutxAtMinDCVDamper = (Min Fan Speed)(adj) set by the user.
Result:
The ERV supply fan can run at a lower speed to save energy when occupancy is low and CO2 levels are normal.
Using the HyperStat DCV damper signal to drive an ERV fan can help improve indoor air quality by supplying the right amount of fresh air.
Taking advantage of the onboard CO2 sensor for this application saves installation costs and time by not having to purchase and install a CO2 sensor.
For Additional Information, refer to:
HyperStat Overview and Installation
HyperStat Conventional Package Unit (CPU)
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