Hydronic heat pumps

By Francesco Lo Presti

People like multi-functional things. You can call, text, take pictures and film movies on your phone. Homes are no different, and we are seeing increased product offerings that cover multiple needs. Hydronic heat pumps are one of these products as they “are not only used for heating, but the newer generation of hydronic heat pumps can also cover a home’s cooling and domestic hot water needs,” explains Chris DesRoches, applied product manager for the HVAC division at Mitsubishi Electric.

Over the last two years, heat pumps have become a central talking point within our industry. Hydronic heat pumps are the next step forward in this transition as they offer homes numerous benefits. The significant benefit being energy efficiency.

The technology
Hydronic heat pumps come in three options: air-source, water-source, and geothermal. “An air-to-air heat pump, aka ductless heat pump, works by absorbing the thermal energy from the outside air and sending it back inside to heat a home. Hydronic heat pumps, more specifically an air-to-water, use that same framework, but instead of pushing air in a home, a hydronic heat pump will use the outdoor heat to heat water,” explains DesRoches.

Going further in detail with the different heat pump types, Mike Miller, vice president of sales for Taco Canada, explains, “An air-to-air can be compared to a furnace since you’re pulling air through a building. If you compare air-to-water, you use outdoor air to generate heated or cooled water. Once you get into water, your choice of heat and cooling emitter type is larger, and you can also use fan coils. But due to the nature of delivering energy via water and small pipes, the zoning becomes easier, as now smaller zoned fan coils can be employed.”

Miller also explains that, “While air-to-air heat pumps, aka a mini-split, provide a home with forced heating and cooling, air-to-water hydronic heat pumps are more efficient as they help generate hot and chilled water and also a more efficient electric domestic hot water supply.”

Popularity on the rise
Regarding heat pump adoption in the Canadian market, “Mini-splits take up most of the market space. But when we dive into hydronic heat pumps, in terms of quantities of units sold into the market, water-to-water greatly surpasses air-to-water that are sold into the market. Probably a 10 to one ratio,” said DesRoches.

Speaking more on why the water-to-water is more used, Miller explains that, “When you’re already heating and cooling water throughout a building, you can transfer the BTUs more efficiently and effectively using the hydronic pipe. Also, with water-to-water or air-to-water, you can take it and make a radiant floor heating and cooling system. You can also install panel radiator, fan coil, and towel rails.”

In a previous edition of our magazine, our writer Michael Ridler wrote an article titled “Heat Pumps Are Not Boilers.” In this, he highlights some of the differences between an air-source and ground-source hydronic heat pump. According to Ridler, “On an air-to-water, the higher the outlet water temperature is from the air temperature, the lower the overall performance of the unit and, in many cases, the heating and cooling capacity. The same is true for a geothermal hydronic heat pump; only the ground loop temperature versus the air temperature will determine overall performance and capacity. A geothermal hydronic heat pump has a higher efficiency but has some limitations regarding where it can be installed due to the requirement for a ground loop.”

A significant difference between hydronic heat pumps and traditional fossil fuel heating technology, like a boiler, is that, “Hydronic heat pumps operate with smaller Delta T’s, so you’ll typically have higher flow rates. Whereas a boiler would operate with bigger Delta T’s and smaller flow rates,” explains DesRoches.

One thing that is very important when working with hydronic heat pumps is understanding the controls and how they work in tandem with the entire system. DesRoches adds, when working commercially, “Heat pumps have compressors, and you want to prevent them from short cycling. So, you’ll typically need a buffer tank in that system to be able to have your minimum run times for the compressors.” In his previous article, Ridler adds, “On a geothermal water-to-water heat pump, we require that buffer tank to ensure the equipment gets a minimum run time of 10 to 15 minutes to maximize its performance.”

Having contractors well-informed on the technology of hydronic heat pumps is essential in promoting the product, but also having contractors ready to install them is another step.

Speaking on this, Tom Heckbert, national sales manager, hydronics and commercial water heating with Rheem, explains that, “With our heat pump, we wanted to make sure that it was a simple installation for contractors. Therefore, we used a monobloc system, where the water and glycol go through the wall, and you don’t need a refrigeration ticket.”

Adoption in Canada
According to Natural Resources Canada (NRCan), around 700,000 heat pumps are installed in Canada. While heat pump adoption has increased, there are still challenges when promoting this technology. “Hydronic heat pumps, more specifically an air-to-water, only heat to -20 C, which means more often you’ll need a form of backup in a home, in places like Ontario, for example,” explains Miller. He also adds that “backups” can come from electrical resistance heaters or fossil fuel-fired equipment.

Currently, there are over five million furnaces installed in Canada. Considering this, DesRoches and Miller added that the retrofit market may be a good bridge for this issue. “With the increase in decarbonization, homes that utilize radiant heating are being told they need to reduce emissions. The best solution would be to utilize your current system and include a hydronic heat pump into the mix. Here you can also make domestic hot water at the same time,” said DesRoches.

Heckbert also explains that having an adaptable system is an important step in adopting heat pumps. He adds, “We still have gas appliances, and we know there are still gas appliances in people’s homes. Air-to-water heat pumps can work with the gas appliances in a hybrid system, and in the future, homes can utilize hybrid systems by adding a heat pump to their current setup.”

Retrofits may be the best solution, but even retrofits can cause some challenges for homeowners and contractors. Referring back to DesRoches’s comments on how a hydronic heat pump operates with smaller Delta T’s, he further explains that, “Contractors might be restricted in how they can integrate a hydronic heat pump into a home because you’re limited with the amount of flow that you can carry through the existing pipes in the building. So that needs to be taken a closer look at.”

In addition, not all homes are suited for a retrofit. “For example, my house was built in the late 80’s, and we have a furnace installed. We wanted to convert that into a heat pump system, but it would be very costly for my whole house to retrofit. Going from nothing hydronic to all hydronic would mean pulling up the floors and putting radiant floor heating down.” Miller adds that the solution for his house was to replace the furnace with a hydronic coil, “Instead of using a flame or refrigerated coil to heat or cool my air, we now use a hydronic coil.”

According to a recent BC Hydro survey, over 30 per cent of Canadians don’t understand how a heat pump works and would be less inclined to upgrade to a heat pump versus a traditional fossil fuel furnace. Making sure contractors are well informed and up-to-date with the technology is critical in advancing the adoption of this technology as, “There is a lot to know about this technology, and contractors need to know that the way you size a hydronic heat pump is different than how you size a boiler,” said DesRoches.

Miller also adds that, whenever a contractor is trying to determine which type of hydronic heat pump will work best for a customer, “You must always start with a proper heat and cooling load analysis on every structure and determine the amount of energy that’s required to heat a house on the coldest day and cool the house on the hottest, and this is for any heating or cooling equipment.”