Simulation of Air-to-Air Energy Recovery Systems for HVAC Energy Conservation in an Animal Housing Facility

Abstract

Implementation of energy conservation measures in buildings can extend our use of finite resources while simultaneously reducing our impact on the environment. This project summarizes efforts to identify economically-viable strategies to reduce HVAC related energy usage and improve the indoor air quality at a facility that houses primates and large cats. The primary focus of energy conservation strategies for the facility centered around air-to-air energy recovery concepts including enthalpy exchangers and runaround loops. Component and system models for transient computer simulations were developed for the existing facility and for several equipment alternatives including enthalpy exchangers and runaround loop heat exchangers. The model of the enthalpy exchanger is based on a new semi-empirical NTU Correction Factor Method. Given only two reference data points, the model is able to predict effectiveness for any balanced and unbalanced flow condition. The runaround loop is modeled as two counterflow liquid-to-air heat exchangers coupled by a heat transfer liquid. The model incorporates liquid flow rate and bypass control. Both models include various options of economizer control and frost control, as well as calculations of parasitic losses. Comparisons of frost control strategies for energy recovery systems were prepared and show that preheating of outdoor air is a favorable solution for enthalpy exchangers. The new simulation models are validated with experimental data. The building model is a detailed model including all internal gains, humidity and solar irradiation and is created in TRNSYS, a software package for transient simulations. The simulations were based on hourly weather data for one year. The simulations allow energy consumption and indoor air quality to be optimized. The findings of the simulations suggest that more than 80% of the heating energy and 45% of the cooling energy can be saved by implementation of air-to-air energy recovery and conservative control settings. The proposal for changes of the HVAC system includes specifications of energy recovery systems and an economic analysis. The environmental impact of the proposed systems regarding CO2 production has been analyzed, showing that up to 73 tons can be saved per year