Questions about heat pump for my shop

[JRP3]

I have a steel 24x32 ft building, (768 sq ft.), with 2 inch spray foam on the walls and 3 inch on the ceiling, (10ft high ceiling), and was thinking of getting a heat pump to keep it above 50F. I have a wood stove but don't always want to deal with starting and tending a fire if I'm just going to work in it for a few hours, and if I don't use it for a few days I don't want the building to get cold soaked. I'm in central NY state. Since I'm not looking to heat up to 70 F most of the time I'm wondering if I can downsize the units I'm looking at, and what my electricity cost might run, or is it better to go bigger to deal with a few really cold days. We mostly see 20-35F but get a few days in the teens and near 0F. Also how the SEER rating would affect my costs. I've looked at some Daikin units that are on sale, I guess they are older units since the SEER rating seems to be lower. Cooling is not a concern as I have good shade in the summer and with the doors closed it's never gotten above 72F.

https://www.heatandcool.com/daikin.html

 

[peakbagger]

This report may be of interest on cold weather operation of heat pumps

(broken link removed to http://vermontfuel.com/heatpump/ewExternalFiles/DOE_inverter-driven-heat-pumps-cold_2015.pdf)

As you will see, they work better if you leave them at one setting. They really do not respond that quickly to varying loads in winter conditions. You may need some sort of supplemental heating if it gets really cold as they really start to run out of heating capacity at temps below zero. Also plan carefully that the outdoor unit is located out of the prevailing wind in spot where snow does not build up or is used to store snow.

 

[JRP3]

I assume the temperature differential matters, so since I'm only heating to around 50F instead of 70F I would still get effective heating below zero, or is my assumption flawed? Also I assume units have improved in the 4 years since that study was done. I was thinking about building a plexiglass enclosure for it to allow solar heating during the day and reduce the effects of wind. I'd have some baffled venting to allow some airflow.

 

[maple1]

I would do it, no question.

Look for a better newer unit though, and if you're comparing numbers, compare COP. We put two Daikins in our house back in November. They work VERY well. Listed COP is almost 5. From some quick googling, the one you linked is just over 3, I think. Looking at more lit, and in other words, going to a newer cold climate unit would give you say 15°f lower outside temp heating ability - and maybe 30% more heat for the same juice used at all operating temps. With this inverter tech I don't see an advantage to downsizing (well, aside from saving a few bucks up front) - they can ramp up and down to meet demand, and the horsepower of higher capacity will likely be appreciated on your coldest days.

 

[JRP3]

Does COP relate directly to SEER?

 

[peakbagger]

Btus are Btus. In order for the unit to move heat out of the outside air there has to be heat in it to boil the refrigerant and the heat pump is starting to have a hard time doing that down below zero. Of course the heating demand of the shop also goes down based on difference in temperature between the inside and the outside and the amount of air infiltration.

Folks need to be careful with getting swayed by COP. COP is not a great comparison tool unless the COP was calculated at the same outdoor temp. The study I linked to shows some definite issues with COP at colder temps.

 

[DBoon]

COP = coefficient of performance. It's a simple BTUs out versus BTUs in at a given indoor and outdoor temperature.
SEER = Seasonal Energy Efficiency Ratio. It's used for AC (cooling) units.
HSPF = Heating Season Performance Factor. It's used for heat pump heating units.

For Central NY heating, I'd look at a unit that can provide heat to -5 or lower outside. Fujitsu (RLS Series) and Mitsubishi (HyperHeat Series) fit the bill. These work very well in a Central NY climate, even on the coldest days.

 

[JRP3]

This Mitsu looks like more than twice the price of a similar Daikin I was looking at:
15K BTU Mitsu https://www.acdirect.com/ductless-a...5-000-btu-heat-pump-hyper-heat-22-seer-system
18K BTU Daikin https://www.heatandcool.com/18-000-...mp-system-230-volt-wall-bracket-included.html
Unless there is better pricing to be found for the Mitsu?
Fujitsu looks to be about the same as the Mitsu. Are they that much more efficient they would make up the difference in cost over time?

 

[maple1]

There is an efficiency difference in those.

 

[JRP3]

Right, but I don't know what that translates to in long term usage costs.

 

[peakbagger]

At least Daikin is a Japanese based firm with legit credibility in the industry. They are a big player in the multihead varible refrigerant flow (VRF) game. I think the bought McQuade. Not sure on how much they do cold climate but they are much better bet than the a generic chinese clones sold under multiple names. Odds are all the big names may be sourcing some or all of their production offshore to lower labor country but its far more likely that they have better sourcing and quality control than a distributor special.

I dont think any of these firms actually design the equipment for repair, if some component breaks the tech just swaps in a new one so the quality had better be in the box when its shipped.

 

[maple1]

Daikin does cold weather heating very well.

 

[maple1]

Right, but I don't know what that translates to in long term usage costs.

I'm not sure I could reliably calc something out either.

But at least on the cost comparison side you should try to compare apples to apples as much as possible.

Unless you are going to install yourself (some have, but I wouldn't), I would start with getting installed estimates for same-spec cold climate gear from local guys. At the same time they should also be able to estimate lower performing units without much trouble. I would stick to Mistubishi, Diakin or Fujitsu. Some guys around here seem to be doing OK with LG but I have also heard of some who have had issues. Compare warranties also.

 

[JRP3]

My plan was to do the physical mounting of components myself but hire a pro to evacuate the lines and hook them up because I understand that's where things can go wrong.

 

[Highbeam]

My plan was to do the physical mounting of components myself but hire a pro to evacuate the lines and hook them up because I understand that's where things can go wrong.

Get the pro on board with your plan. Just like any service guy they often want the whole job so that they can profit from the equipment markup too!

It’s like going into a ford dealership with a dorman waterpump from autozone and the old waterpump removed. Expecting the mechanic to charge you 20$ to install your new one.

 

[JRP3]

Good point. I'll have to do more investigation into a full DIY installation. I plan to eventually put one in the house as well so might be worth the investment in equipment, then sell it when I'm done.

 

[maple1]

Good point. I'll have to do more investigation into a full DIY installation. I plan to eventually put one in the house as well so might be worth the investment in equipment, then sell it when I'm done.

Warranty can also be very much effected by the install. Thinking most need to be installed by 'certified' installers or something like that, for the warranty to be valid. So check that also.

 

[peakbagger]

My understanding is the warranty is covered by the selling dealer. There are dealers on Ebay selling them but I expect they are betting that they will never have to service them so it ups their volume. Not sure Daikin sells the same way. It is highly doubtful if paying a local dealer to do the gas setup entitles you to warranty service through that dealer. I asked a few techs over the years and they all claimed that unless they do the entire install its not covered. Future warranty costs are just factored into the profit they make.

 

[JRP3]

I assume there is a manufacturer warranty. Looking at Daikin they say the warranty only covers if installed by a dealer

What Units Does This Warranty Not Cover?This warranty does not apply to:• Units that are ordered over the Internet, by telephone, or by other electronic means unless the unit is installed by a dealer adhering to all applicable federal, state, and local codes, policies, and licensing requirements.

(broken link removed to https://cms.daikincomfort.com/docs/default-source/default-document-library/warranty/pwddmstwzb_12-7-15.pdf?sfvrsn=13)

 

[maple1]

I can understand that though. Good chance of a messed up install causing an issue leading to a warranty call - they would want some kind of QC type control over the installation.

 

[woodgeek]

I would estimate the BTU/h load from the foamed surface area and thickness. If it was 1200 sq ft at R-8, that would be 1200/8 = 150 BTU/H°F

Heating the place to 50°F when it was 0°F out, would require 150 BTU/h°F * 50 °F = 7500 BTU/h, probably doable for a mini engineered for cold climates.

As for cost...if you heated it with electrical space heaters, it would be 7500 * 24 = 180,000 BTU /3414 BTU/Kwh = 52 kWh, guessing $7-10 per day at +50°F heating.

So I would figure COP = 1.5 at 0°F, and you would save 15 kWh on those days. Your heating would cost 35 kWh/day at 0°F.

At 25°F, you would need half as many BTUs, say 25 kWh worth (if using a space heater) and the COP would be 2.5-3 for a good unit, and heating the place to 50°F would be only 8-10 kWh.

If you wanted to heat the place to a cozy 65°F when it was 40°F, the BTU load would be the same (+25°F), but the COP would be 4, and the cost would be about 6 kWh per day.

I think that a mini would be a very nice and inexpensive solution for you. It would get expensive to use when the COP drops at very low temps...but then you can either pay the bill and use the space, or switch to the woodstove during near-zero °F weather.

 

[woodgeek]

If you want to know the BTU load, you could run a space heater out there for a day or two when the forecast was for steady outdoor temps, and see how much warmer it stays than outside.

 

[Brian26]

My plan was to do the physical mounting of components myself but hire a pro to evacuate the lines and hook them up because I understand that's where things can go wrong.

I did a DIY install a few months ago of a Pioneer unit. They really are not that hard to install. I found the lineset and vacuum to be the easiest part. You can buy all the same professional grade tools that HVAC techs use for around $500. I had most of the stuff like a vacuum pump already so I just needed to but a micron gauge and vacuum rated hose. They DIY route is nice as you can take your time and make sure its done right with no leaks.

It really is as simple as connecting 4 flare fittings and vacuuming the lineset.

All the big manufacturers insist on using a torque wrench on the nuts. I did and everything I read says this assures an extremely reliable flare. Nylog on the flares is also recommended.

Using a micron gauge, valve core removal tool and vacuum pump pull a deep vacuum of less than 500 microns for an hour or so. Turn of the pump and see if the microns hold. A micron is a crazy small precise measurement of vacuum. If there is any leaks or water in the system you will see it fast as the microns rise. Mine held for hours at like 130 microns or something.

After you confirm no leaks you simply open the valves on the condenser and let the refrigerant out. The condensers have the exact amount of r410a in them for usually up to like 15-25 feet on lineset without any need for adjustments.

As far as brands go yes Mitsubishi, Daikin, Fujitusu are no doubt the best top brands. The cheaper Chinese units are actually pretty reliable though if installed properly and are dirt cheap in comparison. The Pioneer unit I bought is actually made by Midea and cross references to a Carrier unit that is actually just a rebadged Midea.

Check out the Pioneer units. The seer and HSPF are actually pretty decent for the price. Though they seem to have a hard time keeping them in stock. These units for the price are highly praised over on the garage journal boards which would also be a good place to do some more research.

https://www.highseer.com/

 

[JRP3]

If you want to know the BTU load, you could run a space heater out there for a day or two when the forecast was for steady outdoor temps, and see how much warmer it stays than outside.

I have a 5600 watt heater that can raise the temp about 10 degrees in an hour. Yesterday it was 23 outside and the heater brought the temp up from 34 degrees to 48 degrees in a little more than an hour. 5600 watts is 19K BTU so I was thinking something around that rating or slightly lower might be good.

 

[JRP3]

Check out the Pioneer units. The seer and HSPF are actually pretty decent for the price. Though they seem to have a hard time keeping them in stock. These units for the price are highly praised over on the garage journal boards which would also be a good place to do some more research.

https://www.highseer.com/

Yeah this looks pretty good, 18K BTU 20 SEER $1K (broken link removed to https://www.highseer.com/collections/wall-mounted-inverter-22-seer/products/18-000btu-ductless-dc-inverter-mini-split-air-conditioner-heat-pump-230vac-20-8-seer-model-wys018gmfi22rl-ahri-cert-energy-star?variant=24482218770496)