SolarWall® with Heat Recovery Ventilators (HRVs)
Designers have asked whether SolarWall® solar heaters and heat recovery ventilators (HRV) can work together and, if so, what are the advantages. The answer is SolarWall systems work well with HRV’s, especially with LEED buildings.
Heat recovery to preheat fresh air may be required to meet the new energy efficiency codes and when designing to these minimum codes, no LEED points are obtained. One must go beyond the minimum requirements and save or generate more energy. It must be realized that only so much energy can be saved and at some point energy must be produced. If you are considering the LEED point for 30% increased ventilation, then renewable energy can play an important role and LEED also allocates additional multiple points for providing this energy from renewable sources.
Please keep in mind that there are design considerations with Heat Recovery Systems and incorporating solar heating may, in some cases, be a lower cost solution than installing more or higher efficiency HRV’s. HRV’s require:
- All exhaust air ducted to supply air location
- Warm exhaust air to be effective
- Space heaters supply additional heat
- Multiple heat recovery units are necessary for large air volumes
- Second fan to bring exhaust air to HRV’s
- High pressure drop for both fans (100 to 400 pa)
- Semi-annual maintenance
- Moving parts with energy wheels
- Frosting problems in cold climates
- Cross air contamination possible with energy wheels
- Susceptible to dirt buildup on heat exchanger
- High initial cost
- Does not qualify for solar energy grants or tax credits
Combining SolarWall to preheat HRV’s is actually a synergistic solution. Advantages of the two technologies working together include:
- Solar preheating virtually eliminates day time frosting problems with HRV’s
- SolarWall pre-filters air before reaching HRV which lowers filter maintenance/replacement costs
- Solar heating HRV combination can provide up to 100% of day time ventilation heating needs
- Solar preheating allows usage of lower cost HRV’s with lower efficiency.
- Typical day time supply air heat gain from solar is 5° to 30° C
- No additional fan requirements for solar
- Low pressure drop for SolarWall (25 to 50 pa)
- The solar component has no maintenance or moving parts
- SolarWall has a 40+ year life expectancy
- It displaces the space heating load during Spring & Fall with free renewable energy
- SolarWall qualifies for solar energy grants and tax credits
- SolarWall Provides dynamic insulation value of up to R 50 on the south wall
Typical solar energy production with SolarWall HRV combination is an additional 30% over HRV’s for daytime ventilation heating (when buildings are typically occupied).