Measured Energy and Demand Impacts of Efficiency Tune-Ups and Thermostatic Expansion Replacements
The overall goal of this study was to assess the potential for cost-effective reductions in energy consumption and peak demand in existing small commercial and industrial cooling systems through efficiency tune-ups. The small C&I customers comprising the primary target group for this study are those with average monthly peak demand less than 50 kW or annual consumption less than 150,000 kWh. The primary source of participants was to be past participants in NEPSCo's C&I lighting program. Analysis of the entire small commercial customer database for a midwestern utility (Dunsworth and Hewett, 1989) showed the typical business with 50 kW of demand to consume 216,000 kWh/year (load factor of about 50%). The typical business with consumption of 150,000 kWh/yr had an average monthly peak demand of about 43 kW (load factor of about 40%). Of the 94 tune-up candidates for whom consumption data were readily available, only five had consumption over 150,000 kWh/yr, four of whom were also over 216,000 kWh year. No demand data were available. The average consumption for the 94 candidates for whom data were available was 55,800 kWh/yr.
The project budget constrained the sample to a maximum of 20 cooling systems at 10 sites. Due to the diversity of building and cooling system types, the small sample size and self-selection bias, the sample could not be statistically representative of the customer base as a whole. However, it was important that the sample include the most common system types and system environments (facility use, ownership types, settings). In addition, it was desirable for the systems and sites to have the characteristics NEPSCo envisions targeting in a future program (possibilities could include a restricted age range, minimum energy usage criteria, etc).
In terms of system types, the primary criteria to be considered were:
The key factors relating to system environments were:
- facility use
- level and type of maintenance
- energy use
In addition, certain criteria were necessary to allow for reliable test results, to protect NEPSCo and its contractors from liability and to keep project costs reasonable. These include:
- absence of supplemental cooling and of rarely used units
- exclusion of certain facility types with high internal gains or with substantial free cooling from refrigeration
- absence of confounding activities
- owner willingness and authority to enter into agreement
- elimination of systems with frequent breakdown problems or with incipient compressor failure
- the number of systems per site since this impacts monitoring costs
Finally, with a tight timeline (four weeks from startup to installation of instrumentation), it was not realistic to aim for an ideally representative sample. Each of these factors will be discussed in turn.
Full report (PDF)
Measured Energy and Demand Impacts of Efficiency Tune-Ups and Thermostatic Expansion Valve Replacements for Small Commercial Cooling Systems