GreenTrust LLC and ICI Homes: Gainesville and Kissimee, Florida

• Evaluate installation issues with a combined tankless gas water and space heating system.
• Evaluate short term performance of the systems in three modes: space heating only, water heating only, and space + water heating.

Madera:

• In space + water heating mode, the circulating pump was unable to overcome the flow resistance through the hydronic coil when two faucets were open, which caused a steady decline in supply air temperature to an unacceptable level. This was despite the fact that the tankless water heater had sufficient capacity to meet the space heating load during the simultaneous use of two showers.
• In the space + water heating mode, however, domestic hot water (DHW) was consistently supplied at 120°F due to the natural priority (via low-flow resistance for the DHW loop) given to water heating loads.
• When the water heater outlet temperature was set too high (i.e., above 140°F), return water temperature above 133°F (manufacturer set point) caused the water heater to turn off. This resulted in short-cycling of the equipment. By lowering the setpoint to 140°F, supply air temperature was 104°F and the cycling issue was resolved.
• The system performed well in DHW-only mode over a wide range of flow rates.

Trafalgar:

• There were numerous installation problems, despite the manufacturer’s installation kit which included instructions and all components for installation. The issues appeared to be mainly due to installation by local plumbers who were not familiar with heating system installation (Florida plumbers do not typically install heating systems).
• Although there was drop in supply air temperature (similar to Madera) during high domestic hot water loads, the higher-head pump reduced the effect.
• The system performed well in DHW-only mode over a wide range of flow rates.