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Exhaust Heat Recovery Study results are disappointing for small, seasonal restaurant, but show potential for larger facilities


A significant amount of heat is wasted through the exhaust ducts of commercial and institutional kitchens in Minnesota. Since the food service sector needs hot water year-round and the need for space heating is limited to the winter season, air-to-water heat recovery has the potential to offer higher energy savings and better return on investment than air-to-air heat recovery in this sector.

Northwinds Sailing, Inc. received a 2009-10 CARD grant to field test the concept of capturing waste heat from kitchen exhaust ducts and using it to preheat the restaurant’s hot water supply. Such a system, if cost effective to install and operate, could potentially be an effective addition to utility CIPs.

The test site was the Angry Trout Café, a small, seasonal restaurant in Grand Marais. The conventional grease filters in the kitchen exhaust hood in the café were replaced with an exhaust-to-water heat recovery system (see figures 1 and 2). Only one product that met the specifications was available and certified at the time of the installation (Dragon Fire Thermo Recovery Filters™). After some initial start-up issues were resolved, this system proved easy to operate and maintain.

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Figure 1. Individual Thermo Recovery Filters used in the study (photo courtesy of Northwinds Sailing and the Angry Trout Café).

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Figure 2. Thermo Recovery Filters installed in the kitchen exhaust hood (photo courtesy of Northwinds Sailing and the Angry Trout Café.)

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Table 1. Summary of system performance for selected scenarios

While the exhaust-to-heat-recovery system appeared to work well and has potential, this study indicates that the manufacturer’s estimates of expected savings and payback for this technology should be evaluated carefully. Larger restaurants and institutional kitchens appear to be the best application. In addition, this technology should be implemented after other energy saving opportunities are exhausted. Although the results were disappointing for this application, this is a first generation technology and the study also suggests that next generation versions may be more cost-effective.

Full results are available in the final report. In addition, George Wilkes, the owner of the Angry Trout Café, welcomes anyone who has questions about the system or wants a first-hand look at the installation to contact him directly either by email or phone (218-387-2137).