Author Topic: HVAC: New heat pump sizing and install  (Read 356 times)

swiper

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HVAC: New heat pump sizing and install
« on: July 23, 2018, 07:52:33 PM »
I’m moving my heat pump as part of a major home reno. Old (disconnected) unit is an old ~15 yr old Carrier 3.5T (38YXA042330)

I was quoted ~10K (CAD) for new heatpump, EV coil with install. Given this cost, I’m considering buying and partly DIY installing the system below. Things are slightly complicated as ordering HVAC equipment in canada seems stuck in the stone ages; so I'll be shipping to the US and driving it up myself.  My plan is to install the evaporator coil, run the lines/wire install pad/bracket for heatpump and cut/install conduit in outdoor wall.

I would hire a professional to check things over, do final hookup, add extra refrigerant and test.

Air Handler: Daikin MBVC1600 with heating strips (Already installed; New 2017)
Outdoor: Heatpump:  Goodman (DSZC160481) 4Ton 16 SEER two stage
Indoor: EV coil : CAPT4961C4 (TXV included in case)

House: ~2800sq (2 story, well insulated with new doors and windows 2018)
Climate: Ottawa Canada (Cold)
AC kick-in setpoint: 26C (78.8F)
Heating:: 16C (61F)
We prioritize heating performance over AC.

Questions:

Are my component choices well matched for the size our home?

I measured the “box” around the old coil and its 20X20. Specs for new one say: 21 X 21 X 30. Does this mean some custom metal box work to make it fit?

Any general advise?

bacchi

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Re: HVAC: New heat pump sizing and install
« Reply #1 on: July 23, 2018, 08:25:18 PM »
What's the low operating temperature for the heatpump? Do you need wind baffles?

swiper

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Re: HVAC: New heat pump sizing and install
« Reply #2 on: July 24, 2018, 04:56:12 AM »
What's the low operating temperature for the heatpump? Do you need wind baffles?

I don't think we need baffles (we aren't in a windy area and the side of the house where the heatpump will sit is well sheltered). I do plan on raising the height of the heatpump to keep it above snow line.

low operating temp, I'm not sure; I understand there is a curve of diminishing heating efficiency as temperature falls. The pump has a HSPF ~9.5 when it is paired with related equipment.


Takk

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Re: HVAC: New heat pump sizing and install
« Reply #3 on: July 24, 2018, 08:02:05 AM »
tldr; You will likely be relying on electric heat during winter months in combination with the heat pump because of the diminishing capacity of the heat pump during winter. during shoulder seasons you will likely be able to rely only on the heat pump. I am assuming you have a minimum of 9.6kw heat strips.

Capacity and efficiency diminishing returns occur all the way down to -10f. Note: Efficiency is always better than running the electric resistance heat in the air handler. so always max out the unit before the resistance coils (heat strips) turn on.

https://www.alpinehomeair.com/related/RT6214005R6%202.2014.pdf

Page 37. bottom left. COP = Coefficient of performance, higher is better. and I'm fairly certain the btuh should be kbtuh (Typo?).


For sizing, http://www.loadcalc.net/load.php
The Manual J calculation is what I use for homes, but my knowledge for sqft based is on cooling down here, so I can't give you a btu/sqft to just go with.

http://cms.ashrae.biz/weatherdata/STATIONS/716280_s.pdf
This is your design conditions. in short, your location goes to negative 21 C. (~ -6F) So your heat pump should be able to operate down to minimum temperatures, unless a cold snap hits hard, but likelihood of that is less than 1% of the year. The question is would it be able to heat your home up enough with only 15kbtu of heat.

Gut check, your sizing is fine. as far as actual installation and compatibility I'm not your man. I'm only the engineering side of that equation.
 

swiper

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Re: HVAC: New heat pump sizing and install
« Reply #4 on: July 24, 2018, 10:00:27 PM »
tldr; You will likely be relying on electric heat during winter months in combination with the heat pump because of the diminishing capacity of the heat pump during winter. during shoulder seasons you will likely be able to rely only on the heat pump. I am assuming you have a minimum of 9.6kw heat strips.

Capacity and efficiency diminishing returns occur all the way down to -10f. Note: Efficiency is always better than running the electric resistance heat in the air handler. so always max out the unit before the resistance coils (heat strips) turn on.

https://www.alpinehomeair.com/related/RT6214005R6%202.2014.pdf

Page 37. bottom left. COP = Coefficient of performance, higher is better. and I'm fairly certain the btuh should be kbtuh (Typo?).


For sizing, http://www.loadcalc.net/load.php
The Manual J calculation is what I use for homes, but my knowledge for sqft based is on cooling down here, so I can't give you a btu/sqft to just go with.

http://cms.ashrae.biz/weatherdata/STATIONS/716280_s.pdf
This is your design conditions. in short, your location goes to negative 21 C. (~ -6F) So your heat pump should be able to operate down to minimum temperatures, unless a cold snap hits hard, but likelihood of that is less than 1% of the year. The question is would it be able to heat your home up enough with only 15kbtu of heat.

Gut check, your sizing is fine. as far as actual installation and compatibility I'm not your man. I'm only the engineering side of that equation.

Thanks that COP chart is interesting, they actually pair the heatpump I want with the slightly larger air handler. I'm going to do some further reading.

I've been getting frustrated posting on HVAC community sites; anything remotely related to DIY is blasted. From some of the guys it sounds like a whole bunch of job insecurity.

Livethedream

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Re: HVAC: New heat pump sizing and install
« Reply #5 on: August 06, 2018, 03:17:42 PM »
What was your quote for, ducting and everything or just the unit and installation? Sounds like you need to get some more quotes if it was just for unit and install. Building our house we got 3 quotes.

#1 wanted to do 2 units for the house about $12k

#2 wanted to do powered ducts to close of sections we didn’t need to cool, can’t remember price but close to $10k

#3 saw we were doing solar and suggested upsizing solar system and going with a single unit that wasn’t “super efficient”  because it was cheaper to cover that with solar then pay for a high seer unit, $6500.