Radiant System Retrofits

Daniel Booy

Mar. 30, 2022

Radiant System Retrofits

I have been designing and building hydronic heat pump systems for over two decades, with many of the systems incorporating radiant heating and radiant cooling. I want to share my knowledge so more people benefit from renewable energy retrofits, with solutions that are the right fit for their application.


Heat pumps are the leading solution for decarbonizing buildings, and we have seen a lot of air-to-air heat pumps or split-system air-source heat pumps installed over the past couple of decades.


I far prefer ground-source heat pumps over air-source heat pumps, for a variety of reasons that I will get to in my next post.


But sometimes geo-exchange just isn’t an option. If you have a hydronic heating system, an air-to-water heat pump will enable you to decarbonize your building without digging up your site to install a geo-exchange system.


Altum has been leveraging the power of direct digital control (DDC) systems and air-to-water heat pumps, in mild climates, with measurable results for several years now. The DDC controllers allow us to remotely monitor and log data, including checking refrigerant temperatures and pressures and electronic expansion valve positions via BACnet.


With the record high temperatures that we had last summer, heat pumps are in high demand for space cooling. Can you use your radiant heating system to cool your building?


With the right system design and corresponding DDC system, yes, you can.


Radiant cooling is often avoided due to concerns about moisture build-up on the pipes.


To ensure that pipes and floors don’t sweat when our systems are in cooling, we use BACnet thermostats to measure the relative humidity in the radiant zones, which enables us to calculate the highest dewpoint in the building and keep the system safely above that temperature.


Our system monitoring has shown that appropriately designed radiant cooling takes the edge off, but we recommend using hydronic-based forced-air in conjunction with radiant cooling if the cooling and/or dehumidification load is large.


Using a three-way mixing valve on the radiant system enables chilled water to be supplied to the fan coil for cooling and dehumidification, while the radiant cooling system is supplied with a bit warmer water for the zone-controlled cooling.


So, yes, you can retrofit a hydronic heating system to be served by an air-source heat pump. But you need to have reasonable expectations of the cooling capacity of stand-alone radiant cooling systems.