Heat Pump and HVAC System

Daikin Altherma

The process began with the architectural drawings, a specification of materials for insulation, and a designer that reviewed the materials to calculate a heat loss of house at design temperature (-20°C or -4°F in Markham, Ontario). Part of the problem was what R-Value and what air exchanges per hour (how leaky the house was) to use for the calculations, since much of this is unchartered territory, and we didn’t want to buy into the marketing hype from all the product manufacturers in terms of each product’s efficiency. In the end, we took a middle-of-the-road approach for each of the materials for R-Value, and assigned a low air exchange per hour knowing that the house was to be very well sealed. For the purposes of the building permit, we came up with an 80kBTU/h heat loss at design temperature, but in talking with our LEED certifier, he feels a house with the selected material will be far lower, perhaps as low as 50kBTU/h.

Our selection of a heating system had to be based on the 80kBTU/h value as we had to satisfy the building code requirements, but also allowed for flexibility to take advantage of a lower heat loss if it were the case. We considered 3 different types of heating system:

  • traditional natural gas fired furnace, for the lowest initial cost but the most energy inefficient,
  • geothermal, for the highest initial cost but also the most energy efficient, and
  • air-source heat pump, for a middle of the road approach in terms of cost and efficiency.

With traditional natural gas fired forced air furnace, we would achieve between 92-98% efficiency (1 BTU in, 0.92-0.98 BTU transferred into the house), but we would be dependent on fossil fuel. The price of natural gas, however, was (and still is) very attractive as it is at the lowest point in more than 5 years, and about 2/3 less than what it was at the peak. In terms of real costs, based on current Enbridge (local natural gas utility) prices as of October 1, 2010, inclusive of delivery and other charges, natural gas is supplied at $0.2666/m³, or $0.024/kWh as of January 2011.

With geothermal, we would be entirely on electricity, using a resistant heat backup. This would get us off fossil fuel (assuming the electricity isn’t coal or natural gas generated), and we would achieve a COP of 3.6 (1 BTU energy in, 3.6 BTU energy into the house), but the primary drawback was the cost of the geothermal system. Based on our location in suburban Toronto, we did not have enough of a lot size to bury the loops horizontally (trenching), but instead it will need to be drilled and installed vertically. The costs of the equipment and installation costs would have been in excess of $35,000 for a 6-ton (72kBTU) system, with the drilling alone representing over $10,000 of the $35,000 cost, and the rebates that were offered at the time only applied to retrofit homes, which we did not qualify. When we compared it to a typical natural gas system and air conditioner which would have cost well below $10,000, the $25,000 difference was hard to justify. Plus, at our 80kBTU/h, we would have required either a secondary system, or an additional electric resistant heat backup to satisfy the building department’s requirements based on our heat loss calculations, as the largest capacity for a mainstream geothermal system would have been 72kBTU/h. In terms of operating costs, the electricity costs vary between $0.08433/kWh to $0.13233/kWh depending on time of day (inclusive of all regulatory charges), so factoring in the COP of 3.6, we would have been barely break even during off-peak use and it would have been 50% more to operate during peak hours, at least given the current lows of natural gas pricing. To spend $25,000 extra with no cost recovery until (or if) natural gas prices rise, this option seems unpalatable.

With an air source heat pump, it works very similar to a ground source heat pump, except that it extracts energy from the air rather than from the ground. For the pump, heat exchanger, and air handler equipment, the costs were similar when compared to geothermal, but because there were no drilling costs involved, the cost of an air source heat pump would be far lower than a ground source. The primary drawback was that the efficiency of the air source heat pump tends to be lower than a ground source, and the output and efficiency of the air source heat pump declines as the temperature drops. In addition, for an air source heat pump, at least for the climate of Toronto, it was very unlikely to have enough output at design temperature unless it was for a small and highly energy efficient house, and as such the cost of the backup system needs to be factored in.

In the end, we chose a Daikin Altherma air source heat pump with a Navien tankless natural gas water heater as backup heat, fed into an in-floor radiant basement heating system and to a Lifebreath Clean Air Furnace with a built-in HRV which acts as the air handler to deliver warm forced air to the main and second floors. A Daikin domestic hot water tank was also installed so that the heat pump can be used for hot water for the house. This hybrid system approach allows us to adapt to a changing energy price market, by giving us the choice to select how low of an ambient temperature to run the heat pump to before switching over to natural gas.  We also plan on adding the solar water kit that would allow us to use the sun to heat the domestic hot water to further increase efficiency.

In our case where the goal is net-zero energy, we would use the Altherma to as low an ambient temperature as possible. But, if our choice was for dollar efficiency, we could choose to run the Altherma when the ambient temperature was around 0°C, where the Altherma was more cost effective with the higher COP, and when the temperature falls below 0°C we would switch to the Navien tankless, with the logic being programmed into the Altherma Hydrobox, with no user invention required.

We chose their ERLQ split system that was rated at 54kBTU, but for our purposes of heating in a Toronto winter, it would only be capable of generating about 25kBTU/h at design temperature of -20°C, and about 37kBTU/h at freezing, which would allow us to be on the heat pump until the temperature dropped well below freezing. Even at -20°C, the Altherma would deliver a COP of 2.5, and at 0°C it would deliver a COP of about 3.0, so while it doesn’t deliver quite the efficiency of a ground source heat pump, the lower initial costs far outweights the reduced efficiency, and it contributes significantly to our goal of becoming a net-zero energy house. In the summer, the Altherma would deliver chilled water to the system for cooling.

When the heat loss of the house becomes greater than the Altherma can handle, the Navien tankless water heater would kick in, supplying up to 160kBTU/h, more than sufficient for any Toronto weather, and also satisfies the building department in terms of meeting the design heat loss.  The Navien tankless unit offers efficiency of up to 98%, which is one of the highest (if not the highest) efficiency available on the market today.

The Lifebreath Clean Air Furnace is a water coiled based air handler that would take the warm water from the Altherma or the Navien tankless, and blows air over the coil to extract the heat into the house.  A built-in HRV is part of the Clean Air Furnace, which we needed because of the air tightness of the house.

Total system cost is estimated to be about $10,000 to $15,000 above a traditional forced air natural gas and an air conditioner, perhaps less as we had an in-floor radiant heating installed for the basement.  Cost recovery as compared to current natural gas rates would be fairly long, but in temperatures of above freezing, the higher COP would be more cost efficient than natural gas, and in the summer the system should be more efficient than a standard air conditioner.  In operating costs, it would be cheaper to operate the Altherma over natural gas when the ambient temperature is above freezing, and would cost slightly more when the temperature drops below freezing, based on the current utility rates.  But the balance point would change should natural gas prices begins to rise from these very low levels.

CaGBC LEED for Homes – Points can be acheived in Energy and Atmosphere, in HVAC (EA 6), or exceptional energy performance (EA 1.2) via the ERS/HERS method.

Update (March 2012) – Through the 2011-2012 winter, we have observed that we were able to continue to run the ASHP and maintain house temperature to as low as an outdoor temperature of -10°C, consistent with the 50kBTU heat loss projection as opposed to the 80kBTU design calculation.

Update (July 2012) – The continuing decline in natural gas pricing has skewed the economic benefits towards natural gas over ASHP or GSHP, so please bear this in mind in considering the cost efficiencies of ASHP or GSHP.

9 Replies to “Heat Pump and HVAC System”

  1. Victor

    A friend of mine is building a home on Vancouver Island (mild winters) and will be using radiant floor heating. I too will be building before long and also using radiant floor heating.

    *Where did you get the Altherma?

    Any “lessons learned” or other insights?

    Thanks

    John

  2. John,

    The milder weathers are much more ideal for an air source heat pump such as the Altherma, and since the Altherma is an air-to-water, it’s ideal for radiant floor heating, and with the domestic hot water option you can heat water at a higher COP as well.

    The major lesson learned is that if you’re in a natural gas serviced area, there’s next to no payback if your electrictiy rates in BC is similar to ours in Ontario. We have time of day usage where at peak ours we’ll need more than a COP of 4 for cost recovery, and at the temperatures that a COP of 4 can be achieved, very little heat is needed anyways. That’s true whether it’s geothermal or air source. But if you’re in an area that’s not serviced by natural gas, then this can be very attractive to propane or to geothermal. The breakeven point to propane is far lower than a COP of 4 since propane is more expensive than natural gas, and with geothermal, the equipment costs are far lower. If you can do a horizontal trench for a geothermal, that gap narrows, but if it has to be vertical (urban lots or on rock where you can’t trench) then an ASHP can look very attractive, even if it’s not as efficient as geothermal.

    The Altherma is unique for an ASHP in the sense that it’s an air-to-water, so for hydronic applications it’s very suitable. In lower BC and the milder climates where the heat loads aren’t as much, the Altherma is likely to supply all the heating needs, and might be a good application.

    We sourced ours through the Daikin distributor in Ontario (http://www.comfortconnections.com). Daikin is very easy to work with, great support from head office in the US, but you will need a competent installer that’s flexible to different systems, as you’re unlikely to find anyone with specific Altherma experience.

  3. Greetings, Victor:

    I am very appreciative of your website – a great deal of helpful information here.

    I would appreciate you sharing details regarding how you are cooling your house. I understand that the Lifebreath Clean Air Furnace can be used for cooling purposes and I also understand that the Altherma can provide cool water. I’m just not sure whether, or how you are using both of these for cooling purposes?

    Thanks,

    Michael

  4. Hi Michael,

    The Lifebreath CAF is the air handler, and it does support a chilled water coil (make sure you order with one). We will be using the Altherma to run the heat pump in cooling mode in the summer, and putting the chilled water through the Lifebreath. Specs on the Altherma says it can output chilled water as low as 40F, and the Lifebreath CAF (when ordered for chilled water) has a pan to catch the condensate for draining.

    Victor

  5. Hi There, I was just on the Life breath Website looking at the Clean Air Furnace, and it appears in their brochures and such that as an air handler, it is set up to run into conventional duct work associated with a forced air furnace (perhaps minus the actual furnace). In most radiant heat installs I have seen HRV’s installed as stand alone units with 4″,5″and 6″ ducting. Did you install conventional forced air ducting to make use of the air handler or doe it run through the typical small volume ducts that are the norm with stand alone air exchange systems?

    I found your site while looking for Daiken Air heat pumps. Love to know how it is still working and whether you have tracked the savings compared with the recent rises in Natural gas prices. I am rural, with two wood stoves so it would likely be just fine for my application (have low mass radiant). My major issues with any heating system is the lack of space for mechanicals in an open concept stone school house. (not built for systems of any sort).

    Thanks
    Lachlan

  6. We installed conventional forced air ducting for the air handler, although smaller than usual size of ducts because of the low heat loss of the house. NatGas prices are 80% less than what we had when we started, so the economic equation has changed considerably. For your application, for rural settings where NatGas isn’t available, then this is a viable choice. If you don’t need cooling, you can run in-floor radiant and the inside system is very compact. Cooling with in-floor radiant wont’ remove the humidity, which is why we went forced air, as cooling was an issue for us for comfort.

  7. Hi Victor and all – I hope you are still out there!
    I’m looking at putting a ASHP system in while renovating my house in Vancouver BC. I have spoken to a number of contractors who have said that the systems are unreliable and prone to interruption/break down and therefore expensive service costs. Has your system been reliable?

  8. Other than a water pump failure (caused by inactivity as the house was vacant for a long period of time, the system has been working fine.

    Look for an ASHP made by companies that don’t manufacture traditional furnaces. Split type A/Cs are very popular in many parts of the world, and those that have heating functions are essentially ASHPs. In fact, ASHP for heating is really an A/C in reverse, so I really do doubt the claims of reliability issues.

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