Estimating Dollar Savings of Utilizing Air-to-Air Heat Exchangers
Course: 22.441 - Thermo Applications
Semester: Spring 2006
Instructor: Majid Charmchi
Partner:Cambodian Mutual Assistance Association
Partnership Description: The goal of this partnership was to assist two community organizations in which students worked in two different groups. One group focused on specific renovation objectives of the non-profit community building owned by the Cambodian Mutual Assistance Association (CMAA) by estimating dollar savings of utilizing air-to-air heat exchangers, sometimes called heat recovery ventilators (HRV). The Architectural Heritage Foundation (AHF), a non-profit developer, is assisting the CMAA in re-development plans with architectural programming. The partnership is working to address the buildings most immediate needs and plan for its renovation into housing and commercial space for locally owned businesses and community services. AHF provided a scope of engineering services to explore and evaluate. The second group of students worked on hypothetical data.
Project Description: Building codes typically require a 15 cfm fresh air intake for every occupant of a commercial building. CO2 detectors can also be used to check for stale air and to control the makeup air rate. The energy consumed in heating and air conditioning this make-up air can be quite high. But a HRV can recover up to 80% of the heat or cooling energy. The contribution of the students involved in the project was to (a) measure the appropriate temperatures and air flow rates in a small HRV that was available in a UML lab; (b) extrapolate the performance of this particular HRV to a larger set of these in the CMAA building with planned renovations with estimated numbers of occupants; and (c) to estimate heating and cooling energy that would be saved in a typical year in Lowell (assumptions were made about the heating/ air condition equipment, and weather records available on the web for typical weather conditions), and (d) translate those energy savings to dollar savings. HRV and related costs were estimated such as payback period, discounted payback, rate of return on investment, and life cycle savings.
Learning objectives met by the S-L project were for students to:
- Experience the design process, including working directly with a community partners
- Heat exchanger analysis and design
- Thermodynamic analysis of: gas power cycles, steam and combined cycles, and refrigeration cycles; mixtures of ideal gases
- Heat exchanges based on hypothetical data as well as real data
- Air-vapor mixtures and psychometric charts with application to air conditioning systems
- Students tested the data and reported on recommendations in terms of heat exchanges for the A/C exhaust and thermal inefficiencies.
- Flow of a compressible fluid through a variable area pass
- Mach number, choking conditions, and normal shock.
- Write technical reports and incorporate analyses
Community objectives met by the S-L project:
- Community partners derived benefit through mechanical design analysis tailored to their specific need.