Energy Savings of Permanent Magnet Synchronous Motors in Refrigerated Cases

- Updated August 2016 to include additional market data and 3rd party lab testing -

In support of California’s strategic plan to accelerate the penetration of energy efficiency technologies, AESC executed a study of a new fan motor technology with funding, guidance, and management by San Diego Gas & Electric Emerging Technologies Program. The primary goals for this project were to determine the energy savings and demand reduction of a permanent magnet synchronous motor with an innovative control design used in supermarket refrigerated cases.

A field trial comprising 9-12W fan retrofits was conducted at a San Diego supermarket. Baseline and retrofit data were collected for 35 and 33 days, respectively, without altering any other system conditions. A baseline of primarily electrically communicated motor driven fans was replaced with PMSM-driven fans. In-situ measurements included monitoring of fan circuit power, case air temperature and humidity, and spot measurements of individual fan assembly power before and after installation. Laboratory testing of airflow and fan curves was also performed for several of the removed baseline fans and the retrofit PMSM model.

The 173 fan assembly retrofits showed clear and consistent improvements in power factor, demand, and energy usage without negatively impacting case operation. The measurements were used to establish annual energy savings and demand reduction estimates. The host site realized a 37% demand reduction and energy savings of the end-use. The saved energy includes both reduction in fan energy consumption and the reduced refrigeration system energy necessary to reject the refrigeration load of the fan assemblies.

Baseline Energy [kWh/yr]                 49,552
Energy Savings [kWh/yr]                  18,278    
Baseline On-Peak FDemand [kW]    5.70     
On-Peak Demand Reduction [kW]    2.16     
Host Cost Savings [$/yr]                   $2,943     
Baseline Power Factor                      54%     
Retrofit Power Factor                        86%     
Apparent Power Reduction [kVA]      4.69 (60%)

Fan savings were determined for medium-temp and low-temp cases and for ECM and shaded pole baselines. Market research showed that existing refrigerated cases are roughly 75% med-temp and 25% low-temp and use about 80% ECM fans and 20% shaded pole fans in California. Furthermore, it was found that the typical supermarket refrigeration systems have estimated COPs of 2.8 and 1.6 for med-temp and low-temp cases, respectively. Using field trial results for each of these case type and baseline fan situations along with weighting using the above factors, the usage and savings per fan retrofit were determined:

Metric                                                Deemed Value
Baseline on-peak power [W]             35.4
Post on-peak power [W]                    20.1
On-peak demand reduction [W]        15.3
Baseline energy [kWh/yr]                  308.8
Post energy [kWh/yr]                        175.3
Energy savings [kWh/yr]                   133.5
Blended utility rate [$/kWh]               0.161
Full installed unit cost [$]                  103
Simple payback [yr]                          4.8

With an idealized 100% market penetration of the 9-12W model, extrapolation to the California retail food segment suggests the statewide savings potential of this technology is about 262 GWh site energy and 30.1 MW demand reduction. The effectiveness, market potential, barriers to adoption, and ease of replacement suggest that this technology should be considered for immediate program inclusion.