A tale of two mini splits

[CapriMikeC]

I wanted to share my experience with installing mini splits for my metal building. Being in the Phoenix area, summers are a trifle warm and winters in the desert can get cold (for a few weeks) so I opted for heat pumps instead of air conditioners.

The building was completed in May 2020 and is 30' x 50' with 12' eaves. Insulation is R-19 at the roof and R-10 for the walls which has kept the temps between 55°-105°F.

After lots of shopping, I bought a pair of Senville Leto 24000 BTU Mini Split Heat Pump - SENL/24CD @ $1099.99 each plus tax through Google Shopping. Each included a 16' line set. Shipping took 3 weeks but FedEx lost the line sets. I contacted Senville and they sent replacements which arrived a few weeks later.

To mount the inside units, I used superstrut from Home Depot so the Senville brackets had something to attach to.




For the outside units, I was advised by a friend to keep them off the ground. Fewer critters, bugs, weeds, and debris. I found these stainless steel wall brackets on Amazon. According to the Senville boxes, they are 105 lbs each and I struggled to heft them on the brackets safely. So my engine hoist did the trick.




For disconnects, I used these from Home Depot.



Line set covers came from Amazon.




This is the last picture I took.



Installation took me 8 hrs each day Sat-Mon over July 4th weekend including the electrical. Both held vacuum and worked as soon as I powered them up.

The building was 103°F at 2pm Monday and 85°F by 6pm. Pretty impressive since there's a lot of mass inside with 6 vehicles and a CNC mill.

 

[Steve W.]

Nice work, and I'll bet that 85° feels rather cool in there.

.

 

[rockcrawler]

Very nice. I’ve been considering two 24K’s for my 35x48x14 in Texas. This is promising. Please keep us updated on the cooling effects these have on your shop. Did it get below 85 at any time?

 

[dougf]

Great write up and pics, I appreciate the time you took to post. Ill be looking at something similar myself!

 

[jcarapet]

I appreciate you providing cost detail and being as thorough as you are. Looking at minisplits for my upcoming 33x60 build. Curious how it holds temp and runs.

Curious, how come you ran with 2 24k units instead of getting a 2 head with single 48k condenser? I was debating that based on availability but was worried about the extra power draw.

Currently looking at this one but have no idea on reputation of website.

MRCOOL DIY Mini Split - 54,000 BTU 3 Zone Ductless Air Conditioner and Heat Pump with 25 ft. Install Kit, DIYM348HPW03C28

MRCOOL DIY Mini Split includes everything you need to cool and heat three different rooms. You'll be sent: 48K Multi-Zone Condenser, three 18K Wall Mounted Air Handlers and three 25 ft. Installation Kits. The best part about all of this is that you can install it yourself!

www.premiumhomesource.com

 

[Digital Spaceport]

I wanted to share my experience with installing mini splits for my metal building. Being in the Phoenix area, summers are a trifle warm and winters in the desert can get cold (for a few weeks) so I opted for heat pumps instead of air conditioners.

The building was completed in May 2020 and is 30' x 50' with 12' eaves. Insulation is R-19 at the roof and R-10 for the walls which has kept the temps between 55°-105°F.

After lots of shopping, I bought a pair of Senville Leto 24000 BTU Mini Split Heat Pump - SENL/24CD @ $1099.99 each plus tax through Google Shopping. Each included a 16' line set. Shipping took 3 weeks but FedEx lost the line sets. I contacted Senville and they sent replacements which arrived a few weeks later.

To mount the inside units, I used superstrut from Home Depot so the Senville brackets had something to attach to.




For the outside units, I was advised by a friend to keep them off the ground. Fewer critters, bugs, weeds, and debris. I found these stainless steel wall brackets on Amazon. According to the Senville boxes, they are 105 lbs each and I struggled to heft them on the brackets safely. So my engine hoist did the trick.




For disconnects, I used these from Home Depot.



Line set covers came from Amazon.




This is the last picture I took.



Installation took me 8 hrs each day Sat-Mon over July 4th weekend including the electrical. Both held vacuum and worked as soon as I powered them up.

The building was 103°F at 2pm Monday and 85°F by 6pm. Pretty impressive since there's a lot of mass inside with 6 vehicles and a CNC mill.

When you say "mass in there" can you go a bit deeper on this? Does having stuff that's say metal create a heatsink of sorts? I have suspected this might be the case.

 

[bonneyman]

Nice clean job on those. High enough off the ground for protection against weeds and such (and snow for heat pumps in an area that has it), but not so high as to make working on them a chore.

 

[yeldogt]

Nice work ..... did you do the evac?

Will be interesting to know two things -- do you hear feel anything with the units on the wall and how well does just having one unit on work.

You have more heat in your climate ..... in PA even on the hottest day my 18k unit is fine for my 1600 sf outbuilding. I don't use it much and keep it at 78 ... but, it will bring it down when needed. I never turn it off due to the humidity in the area --- building is very tight and well insulated

 

[racecougar]

When you say "mass in there" can you go a bit deeper on this? Does having stuff that's say metal create a heatsink of sorts? I have suspected this might be the case.

Yes. If everything inside the OP's building was at 103F, it will take quite a while to bring all of that mass down to a comfortable temperature.

 

[fitter30]

When you say "mass in there" can you go a bit deeper on this? Does having stuff that's say metal create a heatsink of sorts? I have suspected this might be the case.

All the stuff in the space that has to cooled to room temp. Cars, trucks, tools , boxes and even the inside structure. Everything started out at 103° and it was 85° few hours later but the air was that temp the stuff would take longer to get down to temp probably a day or two.

 

[yeldogt]

When you say "mass in there" can you go a bit deeper on this? Does having stuff that's say metal create a heatsink of sorts? I have suspected this might be the case.

This is why it's important to know how a space will be used. If you live in an area with humidity unless you keep the unit running there will be a lot of moisture in the air. Getting that water out requires a lot of capacity over time -- keeping a mini running at 80 will often do it. I do 78 for my spaces. This also brings everything else down to this lower temp. Having some extra capacity is not a bad thing if you have situation where it is often needed. In my case even a hot car coming into 1600 sf is fine -- this may not for a smaller space that's not maintained.

The same is true in the reverse. Trying to heat a full space that's very cold is going to take some time ... especially since the transfer is air.

 

[Digital Spaceport]

This is why it's important to know how a space will be used. If you live in an area with humidity unless you keep the unit running there will be a lot of moisture in the air. Getting that water out requires a lot of capacity over time -- keeping a mini running at 80 will often do it. I do 78 for my spaces. This also brings everything else down to this lower temp. Having some extra capacity is not a bad thing if you have situation where it is often needed. In my case even a hot car coming into 1600 sf is fine -- this may not for a smaller space that's not maintained.

The same is true in the reverse. Trying to heat a full space that's very cold is going to take some time ... especially since the transfer is air.

TY I need to rethink some storage layout things!

 

[Steve W.]

When you say "mass in there" can you go a bit deeper on this? Does having stuff that's say metal create a heatsink of sorts? I have suspected this might be the case.

Yes. If everything inside the OP's building was at 103F, it will take quite a while to bring all of that mass down to a comfortable temperature.

Asked and answered a couple times already, but here's a bit more. EVERYTHING in the conditioned space is going to have a temperature. If the space has been at 103° for a while, it's just like an oven, EVERYTHING will be 103° all the way through. As you start passing 85° air over it, the outer surface cools, which will draw some heat from the core. Eventually, everything will be pretty close to the air temperature.

The same principle works in reverse, too. Once everything is down to 85°, it's going to take a while for it to warm up. This thermal mass helps even out the temperature swings in an area that gets a lot of use.

.

 

[yeldogt]

Asked and answered a couple times already, but here's a bit more. EVERYTHING in the conditioned space is going to have a temperature. If the space has been at 103° for a while, it's just like an oven, EVERYTHING will be 103° all the way through. As you start passing 85° air over it, the outer surface cools, which will draw some heat from the core. Eventually, everything will be pretty close to the air temperature.

The same principle works in reverse, too. Once everything is down to 85°, it's going to take a while for it to warm up. This thermal mass helps even out the temperature swings in an area that gets a lot of use.

.

That's why in general it's best to maintain some temp ......

 

[Digital Spaceport]

Asked and answered a couple times already, but here's a bit more. EVERYTHING in the conditioned space is going to have a temperature. If the space has been at 103° for a while, it's just like an oven, EVERYTHING will be 103° all the way through. As you start passing 85° air over it, the outer surface cools, which will draw some heat from the core. Eventually, everything will be pretty close to the air temperature.

The same principle works in reverse, too. Once everything is down to 85°, it's going to take a while for it to warm up. This thermal mass helps even out the temperature swings in an area that gets a lot of use.

.

I noticed some large temp increases as I moved about 2 tons of steel items into the garage but at the same time it got even hotter outside so I was not sure. This is a 2 car garage turned into a mini datacenter and I need to not have it also be a storage facility for what in essence are extra heat sinks. Running 32K btu of cooling in there had it well controlled, until I moved in the other stuff. Then it was back to hot. Very glad to have a path back to more reasonable temps.

 

[racecougar]

I noticed some large temp increases as I moved about 2 tons of steel items into the garage but at the same time it got even hotter outside so I was not sure. This is a 2 car garage turned into a mini datacenter and I need to not have it also be a storage facility for what in essence are extra heat sinks. Running 32K btu of cooling in there had it well controlled, until I moved in the other stuff. Then it was back to hot. Very glad to have a path back to more reasonable temps.

If you're able to leave the mass in place, it would actually help in maintaining temp/resisting temp change.

 

[Digital Spaceport]

If you're able to leave the mass in place, it would actually help in maintaining temp/resisting temp change.

I need to get the temps as low as possible and the mass of metal stuff is getting ~ 8KW of hot air blown directly on it 24/7 and I dont want to maintain 92F, its unable to be cooled with 32K BTU in an R60 space. It was prior to putting the junk in there.

 

[CapriMikeC]

Very nice. I’ve been considering two 24K’s for my 35x48x14 in Texas. This is promising. Please keep us updated on the cooling effects these have on your shop. Did it get below 85 at any time?

I haven't tried yet. But they pulled 20 degrees in 4 hours in the middle of the afternoon. I'm confident if I left them running with a lower set temp, they would have kept decreasing temp. Also, if I let them run overnight when the sun is down, I'll need a jacket in there.

I appreciate you providing cost detail and being as thorough as you are. Looking at minisplits for my upcoming 33x60 build. Curious how it holds temp and runs.

Curious, how come you ran with 2 24k units instead of getting a 2 head with single 48k condenser? I was debating that based on availability but was worried about the extra power draw.

Currently looking at this one but have no idea on reputation of website.

MRCOOL DIY Mini Split - 54,000 BTU 3 Zone Ductless Air Conditioner and Heat Pump with 25 ft. Install Kit, DIYM348HPW03C28

MRCOOL DIY Mini Split includes everything you need to cool and heat three different rooms. You'll be sent: 48K Multi-Zone Condenser, three 18K Wall Mounted Air Handlers and three 25 ft. Installation Kits. The best part about all of this is that you can install it yourself!

www.premiumhomesource.com

In Phoenix, the higher cooling capacity is only needed June-August. so I may get away with running only one unit the rest of the year. Maybe? I will see how they behave over 12 months.

Nice work ..... did you do the evac?

Will be interesting to know two things -- do you hear feel anything with the units on the wall and how well does just having one unit on work.

You have more heat in your climate ..... in PA even on the hottest day my 18k unit is fine for my 1600 sf outbuilding. I don't use it much and keep it at 78 ... but, it will bring it down when needed. I never turn it off due to the humidity in the area --- building is very tight and well insulated

Yes, did everything myself including the evacuation. I have a pump and manifold I bought to do auto A/C. All I needed was the R410 adapter fitting.

Inside my house, the temp is 78 and the humidity is around 30%. Outside is 109 and 10%. The low humidity certainly makes things more comfortable in the summer.

 

[toyotadriver]

Very clean looking install!

Do you have any issues with the condensing units causing vibration inside the shop?

 

[yeldogt]

I haven't tried yet. But they pulled 20 degrees in 4 hours in the middle of the afternoon. I'm confident if I left them running with a lower set temp, they would have kept decreasing temp. Also, if I let them run overnight when the sun is down, I'll need a jacket in there.



In Phoenix, the higher cooling capacity is only needed June-August. so I may get away with running only one unit the rest of the year. Maybe? I will see how they behave over 12 months.




Yes, did everything myself including the evacuation. I have a pump and manifold I bought to do auto A/C. All I needed was the R410 adapter fitting.

Inside my house, the temp is 78 and the humidity is around 30%. Outside is 109 and 10%. The low humidity certainly makes things more comfortable in the summer.

You don't have the humidity problem in your area --- Humidity requires long run times with AC in my area. Mini splits are perfect for this because of the VS compressors.

In my area --- guess is only having the one uint would be better as it would run low and keep the humidity in check. I would not need two Your climate w/ low humidity having more capacity to bring down the temp faster is not as big a problem -- I'm not sure it saves much.

I wonder how often the space needs more than 24k

 

[CapriMikeC]

So far, I do not notice any vibration from having the units attached to steel walls.

It's 109 F outside today. I set both units to 70 F starting around 3pm. I'll check the shop temperature at sunset and tomorrow evening.

In the desert, the low water results in significant temperature variation between day and night.

 

[CapriMikeC]

The units were set to 86 F (their highest possible setting) and my wall thermometer showed 88 F.

Set both units to 70 F @ 3pm with outside temps around 109, sunset about 7:40pm. Shop is 80 F as of 8:15pm.

I'll update in the morning.

 

[CapriMikeC]

At 3am, the shop was down to 73 F. When I got home after work, the shop is at 83 F with current outside temp of 114 F.

So, if the intent is to keep the shop below 80 F, either larger units are required or better insulation.

However, this is not primary living space and today is essentially worst case. I'm happy with the performance for the cost of the units and how much more time I'll be able to spend out there comfortably.

 

[Slednut]

If the heads are near your work area you can put a large tarp up to divide your shop. I do this and I can leave the garage door open in the area I don't work in and it still stays cool where I work.

 

[kbeefy]

...with current outside temp of 114 F.

Yikes!

 

[racecougar]

The building was completed in May 2020 and is 30' x 50' with 12' eaves. Insulation is R-19 at the roof and R-10 for the walls which has kept the temps between 55°-105°F.

So, if the intent is to keep the shop below 80 F, either larger units are required or better insulation.

Improving your insulation would make a HUGE difference. Replacing the translucent panels with low-E windows would help a bunch, too.

 

[CapriMikeC]

Improving your insulation would make a HUGE difference. Replacing the translucent panels with low-E windows would help a bunch, too.

Yes, you are correct about the insulation. It's reasonable to reduce the load instead of trying to make the units work harder. I'm not sure what's a good and aesthetic way to add insulation. Having clean white walls keeps it bright in there.

These specific Senvilles do not have any built in programming as-is. I'm going to look into one of the smart thermostats or the Senville devices. I think I can run the units at night when the power is cheap and outside air temp is cooler, then in the heat of the day, let the thermal mass coast into the evening.


Some follow up info about the electrical. The units went live on Monday July 4 around 3pm with set temps of 85 F. On Sunday July 10 around 3pm, I set them to 70 F. Monday July 11 3pm, I set them back to 85 F.

Electric the day before powering up the mini splits:



The day the mini splits started working:


My experiment Sunday July 10 setting the units to 70 F:




Setting the units back to 85 F:




My previous "normal" was 60-70 kWh per day. With the mini splits cranked, that can at least double. Set to their minimal cooling, it's about 100-120 kWh per day.

 

[bluedog225]

Great info. Thanks for posting Mike!

Three questions if you don’t mind.

1-did you pressure test with nitrogen?
2-what made you go with these units?
3-why two units and not one larger unit?

Thanks again!

 

[CapriMikeC]

Great info. Thanks for posting Mike!

Three questions if you don’t mind.

1-did you pressure test with nitrogen?
2-what made you go with these units?
3-why two units and not one larger unit?

Thanks again!

No pressure test, vacuum only.

These units were fairly simple without too many extra features and reasonably priced. Getting a single 4 ton unit would be at least twice the cost.

A single unit with multiple "zones" would have been more expensive. Also with two units, I can shut one off when things aren't so crazy hot here.

 

[CapriMikeC]

I did get the Mysa smart thermostat. The one device can control both inside units and I have created a schedule to not run the units during the peak hours when electric prices are high.

 

[TRLKC]

I wanted to share my experience with installing mini splits for my metal building. Being in the Phoenix area, summers are a trifle warm and winters in the desert can get cold (for a few weeks) so I opted for heat pumps instead of air conditioners.

The building was completed in May 2020 and is 30' x 50' with 12' eaves. Insulation is R-19 at the roof and R-10 for the walls which has kept the temps between 55°-105°F.

After lots of shopping, I bought a pair of Senville Leto 24000 BTU Mini Split Heat Pump - SENL/24CD @ $1099.99 each plus tax through Google Shopping. Each included a 16' line set. Shipping took 3 weeks but FedEx lost the line sets. I contacted Senville and they sent replacements which arrived a few weeks later.

Mike, can you provide a 1 year update? I’m looking at purchasing one of these same units in my 24x30 detached stick frame shop. Interested if you’re still happy with them and if you have had any issues?

Thanks!

 

[CapriMikeC]

Yes, still happy with them. No issues.

If I could go back in time, I would have invested in better insulation in the building. That will be a long term project at some point.

Against the current temps, these units take a long time to cool the 30 x 50 building if the initial temp is high. Certainly part of that is the mass of the building and it's contents. If I run the units at night to cool, they will maintain in the low 80s.

Yesterday (Saturday), the units were off. I turned them on to work out there for a short while.




There are two dots about 11am to 2pm showing when I started cooling and when I shut them off and the results. The red ambient temp line is the correct shape but shows cooler than actual temp. Realistically, the room cooled about 5F deg/hr and the start temp was over 100F inside at 11am.

 

[bluedog225]

If not white already, the Cool Roof elastomeric from Henry’s (home depot) is pretty amazing. My metal roof goes from burn your hand hot to mildly warm to the touch. Easy to apply and easy to recoat after 10 years or so. I used two coats. Great for hot summer sun and relatively cheap.

 

[pcmeiners]

Curious, how come you ran with 2 24k units instead of getting a 2 head with single 48k condenser

Not jcarapet's answer but single zone mini-splits are more efficient than multi zone units.