High-Performance Energy Recovery in South-Western Climate: Fundamentals & Examples from Colorado and Arizona
Rudolf Zaengerle, Konvekta USA Inc.
High-Performance Runaround Energy Recovery Fundamentals: High-performance runaround energy recovery systems with advanced control software are operating at efficiencies of net 70-90 percent (based on annual energy consumption for heating and cooling). Advanced control software provides continuous recovery and efficiency reporting and verification.
It's critical that high-performance systems operate at optimum performance under varying operating parameters. With several variable input parameters, controlling and optimizing a system requires a numerical-simulation-based controller that allows variable amounts of heat transfer fluid to be circulated throughout the system. Additional features to optimize latent energy recovery in hot/humid climate add yet another layer of complexity to the control functions.
Designing for high Summer Efficiency including latent Energy Recovery: Any energy recovery system can only be operational in summer (cooling) mode while the air temperature (or enthalpy) entering the exhaust [heat exchanger] is lower than the outside air temperature (or enthalpy). The air entering the exhaust is typically in the range of 72-76F DB, 50-65% relative humidity. In almost any climate zone, there are 2000-3000 hours per year where cooling/dehumidification of the outside air is required, but outside air temperature is below 75F DB, so energy recovery is not possible. If evaporative cooling is added in the exhaust, reducing the DB temperature of the air entering the exhaust heat exchanger to 60-65F, during most of these 2000-3000 hours per summer, cold energy recovery will be possible.
One-Coil Design for Desert Climate:
The desert climate of AZ, NM, UT, CO, WY requires a modest amount of outside air condensation (dehumidification) in summer. Therefore, combining the cooling coil into the energy recovery coil is an elegant solution to minimize fan power and associated electric consumption by eliminating the air pressure loss of a separate cooling coil.
- Understand the underlying thermodynamics of an energy recovery system;
- Identify the difference between instantaneous efficiency and annual effectiveness;
- Understand the benefits of indirect evaporative cooling and its impact on annual operating hours; and
- Understand the drivers impacting the one-coil decision.
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