Help selecting a heat pump
I’m going to be meeting with my builder this week, and he wants to show off the furnace of his choice, which is a Dettson Chinook. It’s a small modulating natural gas unit, that can be paired with their Alize heat pump.
It’s a pretty neat unit, designed to allow for very long cycle times, often measured in hours. The problem I have is that the heat pump portion kind of sucks in cold weather, it uses proprietary small high velocity ductwork, and a proprietary thermostat to control it all. It also has a short~ish warranty.
I’m really trying to hit Net-Zero. I’m expecting load at 99.6% design temps of -20C to be a little under 27k BTU.
I think I’d like to pitch two different units to the builder, and I’d like to hear what you guys think.
1) Trane XV18, 3 Ton, HSPF of 10. The Trane XV18 series is rated as a cold climate air source heat pump by the NEEP. The unit will put out 20k BTU at design temps, and would modulate to perfectly match the load and carry the house down to -12C, and happily continue running down to -25C. The HOT2000 application I’m using for modelling predicts I’ll use about 50 kWh of aux heating in the average year. I think I can afford the $5. Equipment cost is around $6k CDN + install.
2) Mitsubishi Zuba Central, also a 3 ton. HSPF of 11. Thanks to Mitsubishi’s hyper heat, this thing will happily cover the entire heating load well below design temp, but it doesn’t have as large a turn down ratio, so I think it’ll end up cycling a lot more. Minimum output is 18k BTU, 2/3rds of design temp. Equipment cost is about 8k. The Mitsubishi puts out more heat at low temps, and does it with a higher COP, but is a bit more expensive, and doesn’t modulate as well.
My builders concern is that “with these heat pumps the aux strips will come on, and you’ll spend a lot of money”, but I don’t think that this is true, especially with the Zuba unit. What do you guys think?
Minisplits are out, because the lot is tight, so the house is built up instead of out. There are three floors plus a basement that need heating, and a Mitsubishi miniplit starts at around $4k each, installed, making my HVAC a lot more expensive, really cutting into my heating budget, and that still wouldn’t really get my great coverage on the floor where most of the bedrooms are. I’d rather spend the extra $8k on my solar array.
I’m leaning the Zuba central unit, but I’m concerned that I won’t get the rated performance, as most of the shoulder season, 18K BTU is going to be too much, and during the cooling season, 18K is going to be a lot. 18k is my cooling design load. I will have a heat pump water heater to help a bit with dehumidification. The Trane unit however, will modulate down to 8K BTU in heating or cooling, so the house will probably be more comfortable, and I’m more likely to get the rated performance with nice long cycles.
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