Cold-Climate Air Source Heat Pump
We live in Ottawa, Ontario (zone 6) and want to stop directly burning fossil fuels. That means replacing our townhome’s natural gas furnace and hot water heater with electric.
Our plan has been to replace the furnace (two-stage 28,000/40,000 BTU) and existing AC (18,000 BTU) with a ducted ASHP. After researching and speaking to some contractors, we had settled on the Trane XV19 because it’s compact and quiet. The proposal we have is for the 24,000 BTU XV19 and the TAM Air Handler with 15 kW heat strips (models 4TWL9024A1 / TAM9A0B30V31DA).
However, we now realize that the Trane is not a cold climate ASHP and we are concerned about the operating costs and performance in coldest weather. That’s because it appears that if we are going all electric in our climate (heating design temp = -13 F), we have to trade off between three things:
1) Sufficient ASHP heat output
2) Cost of backup electric resistance heat
3) The need to avoid oversizing the ASHP so that the cooling does not “short cycle”
All insights welcome and we particularly seek answers to the two related questions in the title:
1) Do we need a cold climate heat pump to help balance the heating and cooling performance in our climate?
2) What BTU output should we get?
Many thanks in advance!
** For those who dive deeper with data and arithmetic, here are lots of further details:
– Home built to energy star standards in 2019 – we bought in 2020 so have lots of accumulated data
– 1,450 sq feet over 4 levels
– Footprint is 12′ W x 42′ deep (heated space is all of top 2 levels and half of the ground floor and basement)
– Long walls are shared on both sides with attached townhomes so very low exterior surface relative to heated space
– Lots of passive solar heat all year round – front is south-facing and 50% energy-efficient windows
– Design loads for the home
– 39,500 BTU for heating – furnace is two-stage 28,000/40,000 BTU
– 17,00 BTU for cooling – AC is 18,000 BTU
– Design temps for our location
– Heating = -13 F
– Cooling = 86 F
– HDD are 8,000 F
– Heat load calculation (using https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler)
– Balance point 65 F
– Meter reading data from Jan 5 – Mar 4 (our gas utility only reads every 2 months) minus known summertime gas consumption for hot water only
– 9,691 average BTU/hr
– Ecobee settings and data records
– Settings are 70 F from 7:00 am – 5:00 pm, 72 F from 5:00 – 11:00 pm, 61 F 11:00 pm – 7:00 am
– Furnace only ever works at first stage
– Other than the warming to higher set points, the furnace runs very rarely
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