Modern low-ambient, mini-split heat pumps offer the promise of providing both heating and cooling without the cost associated with duct retrofit. It is common for these heat pumps to be installed alongside an existing hydronic heating system, often oil-fired.
The National Oilheat Research Alliance’s (NORA) just released Development of a Best Practices Guide for Integrated Hydronic and Ductless, Air-source Heat Pump Systemsstudied the operation of a hybrid systems of this type. The goal of this study was to provide a guideline (Best Practices Guide) for control strategies that would provide greatest efficiency while maintaining comfortable heating of the home. This was achieved through performing field tests and an annual performance analysis.
The field tests provided a baseline understanding for creating the Best Practices Guide. Data collected from six sites across New York State provided insight into how the hybrid systems are currently configured and operated. Based on this, and a set of performance data for various boilers and heat pumps, an annual performance analysis was performed. This component of the study simulated cost and energy usage for various combination of heating appliances (heat pump and oil-fired hydronic) for different control methods that were chosen.
In most cases, the heat pumps were installed for enhancing comfort in a small part of the home and control of the switchover between the two systems was casual. Cost savings associated with the heat pumps were not found to be significant. Higher efficiency hydronic systems were found to be favorable relative to typical heat pumps.
The study was conducted and authored by Neehad Islam, Dr. Thomas A. Butcher & John Levey for NORA and was submitted to the New York State Energy Research Development Authority, a prime funder of the research. The 105-page report on the study and its findings can be accessed here.