There is a movement afoot to wean off of fossil fuels. We see more and more cities, even entire countries, heading towards an all-electric energy future. There are also some pretty interesting vehicle offerings, if you happen to be a hydronic-maniac and a motorhead. As a hydronic and comfort industry, we need to determine how we can still have a seat at the electrification table. To keep a fluid-based (hydronic) offering, what are the electric options available today?
Electric boilers are an option in areas with low-cost electricity. I will say that industry has evolved from the electric boilers I first installed and worked on. Microprocessors and digital controls allow for small, quiet, modulation electric boilers in a wide range of sizes. Electronics on board allows for outdoor reset functionality and contactor-free staging of the elements. There are some top-notch brands manufactured in Canada, if you have a need for electric element boilers.
When we offer a hydronic system, efficiency will continue to be a buzz word for our customers, and may be a close second priority to comfort for many home and building owners. Heat pumps (HPs) are another option that are getting a lot of attention from contractors as well as product designers and manufacturers. If we want to keep hydronics in play, and we do, we need to find and offer options to heat the fluid via electrically powered equipment. Simply put, heat pumps have the ability to leverage or multiply the source − air or water − and provide additional output. In Caleffi’s Idronics 27, a refrigerator is used as an analogy, to demonstrate how we can reverse the natural direction of heat transfer.
We pull low temperature heat from the food inside, and expel it to the surrounding air. With this same technology, an A2WHP can pull energy from the surrounding air and use it to heat a fluid for powering a hydronic system. So, is it possible to remove a fossil fueled boiler and directly substitute an air to water heat pump?
Understanding the acronyms
Let us take a look at some of the current technologies and get a few terms defined. You will see A2WHP: it means simply air to water heat pump. Another acronym you may see is ccA2WHP. It stands for cold climate air to water heat pump. Heating seasonal performance factor, or HSPF, describes the efficiency of a heat pump over a heating season. To get the rating, you take the total heat output. Then, you divide it by the total electric output during that same specific period. Overall, the higher the HSPF rating of a unit, the more energy efficient it is.
Check out Adapting heat pumps to our Canadian climate from Natural Resources Canada: https://www.youtube.com/watch?v=-wTRGbDY7Kk
Will an HP cover the load?
Here are a few considerations to help determine if and when an HP can be substituted for a boiler. Tattoo this somewhere on your body: it’s all about temperature. Those among us who have embraced condensing boilers or mod-cons should know the lower the operating temperature condition, the higher the boiler’s efficiency. Apply this logic to heat pump applications.
Steps to take:
- A load calculation on the building in its current state. This is always the roadmap to a successful outcome.
- A survey of the current heat emitters to determine their output at various supply water temperatures (SWTs).
- Upgrade the structure. This is the best money spent, always. Maybe perform a blower door test, an infrared scan, to find and seal infiltration gaps. Recalculate the load after any improvements to the structure.
- Select a heat pump model and see if it can efficiently cover the load and produce the SWT required at design conditions.
Supplement areas with low temp emitters
I predict you will find applications where the current offering of heat pumps may not adequately or efficiently cover the load across all conditions. In other words, they cannot provide the required SWT for design, coldest day conditions but all is not lost. You may be able to increase the emitters, as heat transfer is always a surface area game. Allow me to refer to you a new tattoo: add or increase fin tube area. You could upsize a forced air coil, or supplement areas with low temperature panel radiators. You could add radiant surfaces, arguably the lowest possible heat emitter option, on walls and ceilings perhaps.
And more helps is on the way. Manufactures are hard at work developing heat pumps to reliably and efficiently produce 180°F equipment.
My goal, our goal, should be to comfortably heat a space, any space, with 120°F or lower SWT. When we get to that number we can leverage several proven options. Solar thermal comes back into current A2WHPs, and waste heat recovery. John Siegenthaler (Siggy) refers to these low temperatures design as “future proofing” your building.
An interim step
Hybrid systems may be a solution until the powers that be completely shut off the pipelines. You can run the heat pump to the best efficiency temperatures, and bring on a boiler for the days the heat pump struggles.
System utilizing electric boiler, heat pump, buffer tank and radiant panel circuits
As shown here, the refrigeration system is on. Hot refrigerant gas is circulating from the outdoor unit through the refrigerant-to-water heat exchanger, which is functioning as the condenser. Heated water is flowing into the buffer tank. Heated water is also being extracted from one of the upper connections on the buffer tank and routed through the 3-way mixing valve to the radiant panel distribution system. This water flows through an electric boiler, which may or may not be operating as a supplemental heat source depending on the required supply water temperature to the radiant panel circuits. This system can also provide chilled water for cooling.
A key hydronic component will be a buffer tank. Current heat pump selections do not have the modulation ability that we have come to understand and love with mod cons. We really do not want to excessively cycle the heat pumps, and micro-zoned jobs will need some careful design considerations to eliminate cycling. HP manufacturers will spell out an acceptable cycle.
Here are a few things to look for, or adjust for, in a successful A2WHP/ boiler replacement: adequate capacity in the breaker box, low temperature emitters, buffer tank, and location for the outdoor equipment.
There are some excellent training materials and YouTube videos out there to help you learn the pros and cons of A2WHP applications. Numerous Canadian companies are working on products specifically for the conditions common in the sometimes-frigid north country.
Ask good questions, and seek out testing sites. Learn about refrigeration technology design and specifically troubleshooting and repairing. Position yourself at the front of this curve and become an expert in designing and applying.
Don’t get shocked by the electrification movement. It should sound like opportunity knocking.