Hot Water Recirculation Controls in Hospitality Buildings
Ben Schoenbauer, Dave Bohac, P.E.
For the second phase, the project team installed the demand control system and monitored six sites to evaluate the domestic hot water system, identify specific controller installation issues, characterize the pumping patterns in centralized hot water systems in different building types and calculate the savings for demand controlled recirculation. The project team analyzed the data and found that on average the controller reduced water heater consumption 13%, and pumping energy consumption by 87%. Download the full report.
Why this research is needed
Aquastat and time clock recirculation loop controls are used to reduce pumping and heating costs, but these controls work on a pre-set schedule and can delay hot water access during low use periods. This can be a particular concern in the commercial hospitality sector, where hot water usage patterns are highly variable, leaving the owner with little choice than to bypass time clock based controls so that hot water is always immediately available to satisfy their customers.
Newer systems use more sophisticated controls to improve response time. They register both temperature and demand so that the controller activates recirculation when both the return water has dropped below a prescribed temperature, and when hot water demand is sensed. Demand controls can quickly deliver hot water during low use periods.
Project process and expected outcomes
Researchers will assess the effectiveness of new demand control systems in hospitality and commercial buildings. The first project phase, now being completed, will characterize existing systems. A nonintrusive data acquisition system will measure the recirculation pump runtimes, electricity use, and loop water temperatures at ten to fifteen buildings. Short term monitoring will evaluate the proportion of buildings on continuous loop operation, identify specific issues, and characterize the pumping patterns in centralized hot water systems in different building types.
In the second phase, the project team will install demand control systems at six hospitality and commercial buildings in Minnesota. System operation will rotate on a weekly basis between the new demand-based system and the baseline existing system, with detailed monitoring over the course of 10-12 months. Results will be used to determine the energy savings, estimated payback period, and percentage reduction in pump run time and hot water delivery time during low use periods.
*This project supported in part by a grant from the Minnesota Department of Commerce, Division of Energy Resources through the Conservation Applied Research and Development (CARD) program. And with co-funding by CEE in support of its nonprofit mission to advance research, knowledge dissemination, and program design in the field of energy efficiency.