30 Mechanical Minutes: Episode 16 "Air-to-Water Heat Pumps"

HPAC Magazine's editor Doug Picklyk sits with hydronics industry expert John Siegenthaler to talk about Air-to-Water Heat Pumps for the residential market in Canada. The discussion covers exactly what air-to-water heat pumps are, what's available today, how they operate and some system design considerations.

[@tlangdon12]

In Europe, many manufacturer are recommending Anti-freeze Valves instead of anti-freeze fluid. Anti-freeze fluid lowers the performance of the system whereas anti-freeze valves don't. The valves need to be good quality and protected from water & snow. They are fitted on the supply & return lines to the outdoor unit outside of the home. They release some water from the system if the outside temperature drops below 38F. If the outside temperature is below 38F, you can be certain that the heat pump will be running UNLESS it has a fault or there has been a power cut. If the heat pump is running the valves won't open, but in the even of a fault or power cuts they will open just enough to let a little water out to stop the outdoor unit from being damaged. The system needs to be topped up when the fault or power is restored, but you only need to top it up with fresh water, not a solution of water and anti-freeze.

[@GIddyUpRetep]

I totally agree with what was said at 10:49. You can use bivalent system and use the heatpump for the majority of the year...then use the existing boiler just a few times a year when it is really cold. Somewhat common to use this approach in the UK. We shouldn't let perfect be the enemy of good.

[@GIddyUpRetep]

Update: I just looked into to John's bio and saw he wrote an article in PMMag title "Options for connecting heat pumps to existing boiler systems". This article has great diagrams showing the different options to combine a heat pump and boiler. Such an awesome resource! I had been contemplating the design of my system in my head/imagination based on my limited knowledge...but I had never seen an example diagramed out in a picture...I am so happy to find this article with several diagrams to show my boiler guy. It would be great if there was also an option to add in a hotwater heater...perhaps with a heat exchanger?

[@GIddyUpRetep]

They talk more in depth of this at 15:39. AKA dual fuel or bivalent.

[@moamaralhoushan3219]

Thank you so much. Enjoyed the talk and it has a plenty of valuable info. How to test the performance of an Air to Water heat pump, scoop seeer and all stads testing

[@tlangdon12]

Brilliant video! So much ground covered in just 40 minutes.

[@hpacmag]

Glad you enjoyed it!

[@tlangdon12]

Panel radiators are very common in Europe and the UK in rooms where the home owner want thick carpets and thick underlayment. Combined with simple Thermostatic Radiator Valves, to avoid overheating due to thermal gain, they can be a very cost-effective solution were cooling isn't required. Radiant ceiling or fan coils are the best emitters for cooling applications. Radiant floors or panel radiators are the best for heating. Radiant walls might be a good in a few limited situations, but my sense is that there is more risk of a nail through a wall than through a floor or ceiling.

[@Chris-c2o]

John’s graph showing temperatures vs distribution equipment (around 10min mark) should have a dotted area instead of line at 120F for baseboards. The line implies can’t use below 120F when you can. It really depends on extent of weatherization, outside temp & set point. Here’s an example of old 180F baseboards powered by AWHP & well below 120F; start around 23min in kzbin.info/www/bejne/b4SwqZSFgr1gpbs 9:58

[@tlangdon12]

If the designer follows the manufacturers recommendations for minimum fluid volume in the system, defrosting should not produce a noticable drop in termperature indoors, but North America typically has homes with much lower thermal mass than the UK or Europe, so it could be more of an issue in North America. A system volumiser or buffer tank is a reasonable solution, but in the UK some experts are actively trying to design out buffer tanks (and zone valves) from their systems. Perhaps the ultimate buffer tank configuration is no buffer tank! Great to hear that in John's experience home owners don't experience any cooling when the system is in defrost.

[@SimonMark-s4h]

Has this system been proven to withstand the extreme winter conditions in Fernie, BC, where temperatures can reach -35°C for consecutive weeks? My planned house is around 3,500 sq. ft., including two 600 sq. ft. suites, two en-suite bedrooms, a top floor measuring 20' x 58', and a smaller attic.

[@rcpmac]

I would have loved to have seen a specification for a hybrid system retrofit designed for a residence located in western NY southern Ontario region equipped with an existing forced air natural gas 100kbtu furnace and a typical 50 gallon mf DHW unit. The hp would be required to provide primary heating and cooling and domestic hot water. This is going to be a typical existing residential profile for many homes in the region. Can this be accomplished in a way that makes sense economically?

[@tlangdon12]

The Global Warming Potential of R410a is 2088, for R32 it is 675, for R290 (Propane) it is 3, and for R744 (CO2) it is 1. Propane is pretty much the ideal refrigerant for small residential monobloc systems where all the refrigerant can be kept outside of the home; although CO2 is better for high temperature applications. For split systems and larger commercial systems, Propane is not ideal and an alternative refrigerant is preferable.

[@rcpmac]

Radiant ceilings from an occupant perspective in my limited experience, has a low comfort factor. Floors hav a high comfort level

[@tlangdon12]

Another solution to the two buffer tank question is two heat pumps: one for space heating/cooling with a single buffer, and a ducted Heat Pump Water Heater for hot water. The ducted Heat Pump can be a CO2 model, so able to heat domestic water to a point where Legionella is not a concern. This avoids the need for the space cooling heat pump to have to switch to heating mode to keep a supply of hot water ready for use. This configuration also allows the heating heat pump to operate at maximum efficiency in heating mode because the flow temperature can be controlled by outdoor reset.