3 mini splits vs central ducted in large shop

[PurdueSD]

My HVAC guy is pushing me towards the mini split option. Im kinda leaning towards the conventional. Heat and air. Heated to constant 55/60in the winter,
only AC maybe 2 months a year. Glass doors and windows are insulated. 42 x60 with a 12x38 lean to.

The price is the basically the same for either option. I have zero experiences with mini splits. What do you guys think?

Here are my options:

Bryant Equipment:

22.4 SEER Mini-split
2-2 ton Heads
1-1-ton head
3 line sets
3 remote control tstats
All labor

VS.

14 SEER Heat Pump 4 ton
Electric backup
T-stat
Spiral Duct Work
Registers
Base with return grill

 

[Firebrick43]

Mini splits, much more efficient below 40 degrees, some what more efficient all the time, better dehumidification during the summer, and I one unit fails you still have heat/ac. I would go with 3 seperate mini splits and stack the outside units, should cost no more than a multi zone, and are typically even more efficient plus you have back up.

Do you know that domestic branded mini splits are typically rebranded gree (Chinese) units?
Not bad per say but you are paying more for a name and many times you can get the Mitsubishi/fajitsu/daikin premium models for the same money

 

[theoldwizard1]

Bryant Equipment:

22.4 SEER Mini-split
2-2 ton Heads
1-1-ton head
3 line sets
3 remote control tstats

First, the most popular brand of mini-split are Mitsubishi and Fujitsu. They have been in the business the longest. Mitsubishi has been selling their low-temp system (good to below 0F) for a number of years. Check your specs !!

Are these "heads" all run off of one compressor, or are will you have 3 compressors. Long line sets are expensive and you lose efficiency.

VS.

14 SEER Heat Pump 4 ton
Electric furnace

STOP RIGHT THERE !!

Electric resistance heat is the MOST EXPENSIVE FORM OF HEAT TO OPERATE ! This may look like a good deal, but it will cost you $$$ every time that heater kicks on !


I always recommend a "backup" heat source for any building that is all electric. Propane space heater would be adequate.

 

[PurdueSD]

First, the most popular brand of mini-split are Mitsubishi and Fujitsu. They have been in the business the longest. Mitsubishi has been selling their low-temp system (good to below 0F) for a number of years. Check your specs !!

Are these "heads" all run off of one compressor, or are will you have 3 compressors. Long line sets are expensive and you lose efficiency.


STOP RIGHT THERE !!

Electric resistance heat is the MOST EXPENSIVE FORM OF HEAT TO OPERATE ! This may look like a good deal, but it will cost you $$$ every time that heater kicks on !


I always recommend a "backup" heat source for any building that is all electric. Propane space heater would be adequate.

You are reading into that wrong, the backup heat is strip heat. Primarily a heat pump.

Thanks for the input, I've got some questions on the specs of the mini splits that I'm waiting to hear back on. But these minis are supposedly good down to 0 also.

 

[PurdueSD]

Mini splits, much more efficient below 40 degrees, some what more efficient all the time, better dehumidification during the summer, and I one unit fails you still have heat/ac. I would go with 3 seperate mini splits and stack the outside units, should cost no more than a multi zone, and are typically even more efficient plus you have back up.

Do you know that domestic branded mini splits are typically rebranded gree (Chinese) units?
Not bad per say but you are paying more for a name and many times you can get the Mitsubishi/fajitsu/daikin premium models for the same money

Ya ill have to look into that. They don't sell the Mitsu units so ill have to talk to somebody else. DO you see think the 2 2 ton mini's can circulate enough air in the big part of the shop? Im guessing no, and ill need fans. Thanks for the input!

 

[Marctrees]

Perdue - You sed.... "You are reading into that wrong, the backup heat is strip heat. Primarily a heat pump."

Isn't electric resistance "strip" heat totally diff than "heat pump"??

I am not an expert on this, will not comment further, but something did not sound right to me.

For "strip" heat, you need electricity.

For heat pump heat, in my ignorant terms, it's an AC running "backwards", NOT an electric generator or other source powering resistive heating filaments.

I dunno further, Marc

 

[Marctrees]

Other than..... ( I keep talking....) It would seem Propane ( if no Natural gas available) would be WAY smarter for heat where you are located. Marc

 

[PurdueSD]

Perdue - You sed.... "You are reading into that wrong, the backup heat is strip heat. Primarily a heat pump."

Isn't electric resistance "strip" heat totally diff than "heat pump"??

I am not an expert on this, will not comment further, but something did not sound right to me.

For "strip" heat, you need electricity.

For heat pump heat, in my ignorant terms, it's an AC running "backwards", NOT an electric generator or other source powering resistive heating filaments.

I dunno further, Marc

Heat pumps work for heat yes. Yes the system basically runs backwards. Electric strip/ resistance heat is a totally different thing than a heat pump.
A heat pump is one of the most common types of heat in my area. I would choose NG over a heat pump, but that is not an option. Yes i could use propane, but a heat pump is more affordable when you do the math for my area. I installed a hybrid system with backup propane at another property, its great. However Im hoping to avoid setting a propane tank at the location. SO i am ok with the tradeoff of using strip/resistance heat as a backup.

A heat pump is a device that transfers heat energy from a source of heat to a destination called a "heat sink". Heat pumps are designed to move thermal energy in the opposite direction of spontaneous heat transfer by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses a small amount of external power to accomplish the work of transferring energy from the heat source to the heat sink.

 

[PurdueSD]

Now, getting back on track, if anybody could help:

Will (2) 2 ton Mini splits be able to evenly heat a 42'x60' shop?

Will they create enough airflow, or will i need fans?

 

[Firebrick43]

If you set them in diagonal corners I would say yes, depending on the models. If will help form a circular current that will mix things better. I only have hands on experience with Mitsubishi but the vanes in the grill move side to side and up and down. The top model also has infrared sensors and see people(and adjust accordingly).

Wife's friend has a large open floor plan house and I still can believe how even every thing is with one mini split.

You can always mount a fan box or two now and it will be an easy addition if the circulation doesn't meet your expectations.

 

[dsimatt]

Now, getting back on track, if anybody could help:

Will (2) 2 ton Mini splits be able to evenly heat a 42'x60' shop?

Will they create enough airflow, or will i need fans?

It's surprising the air flow my single 18k unit in my house does but it does take time to cool the main living area and a few hours to push the air to the other end of my house.

What are you plans on using it, if you maintain a decent temp and then want to change it a few degrees you'll be ok but if you want bigger changes quickly then you'll be disappointed I think.

 

[Ray-CA]

No matter which source you decide on, I'd install a couple of ceiling fans instead of using box fans.

Ray

 

[mrpizza]

I would go with 3 seperate mini splits and stack the outside units, should cost no more than a multi zone, and are typically even more efficient plus you have back up.

Looking at my price sheet at work, a multi zone outdoor unit is only a couple hundred bucks more than the single zone outdoor. If you do multiple single-zone systems, you are buying an outdoor unit for each. Much more expensive.

 

[yeldogt]

Carrier/ Bryant is rebranding someone's mini splits -- find out who they partner with.

I'm surprised you can't get a better conventional system for the same price as the mini -- I can assume you don't have NG at the location?

The mini's do work very well -- how dirty is the area?

 

[theoldwizard1]

You are reading into that wrong, the backup heat is strip heat. Primarily a heat pump.

MOST "central" heat pumps will kick on the heat strip when temps go below about 32F.

 

[PurdueSD]

If you set them in diagonal corners I would say yes, depending on the models. If will help form a circular current that will mix things better. I only have hands on experience with Mitsubishi but the vanes in the grill move side to side and up and down. The top model also has infrared sensors and see people(and adjust accordingly).

Wife's friend has a large open floor plan house and I still can believe how even every thing is with one mini split.

You can always mount a fan box or two now and it will be an easy addition if the circulation doesn't meet your expectations.

No matter which source you decide on, I'd install a couple of ceiling fans instead of using box fans.

Ray

Thanks, i think a couple ceiling fans would be smart regardless.

 

[PurdueSD]

It's surprising the air flow my single 18k unit in my house does but it does take time to cool the main living area and a few hours to push the air to the other end of my house.

What are you plans on using it, if you maintain a decent temp and then want to change it a few degrees you'll be ok but if you want bigger changes quickly then you'll be disappointed I think.

Ya, im kinda in to slow temp changes either way i go. Without using gas, I'm going to need to stick to a more constant temp. I think thats easily doable for my needs. Thank you!

Looking at my price sheet at work, a multi zone outdoor unit is only a couple hundred bucks more than the single zone outdoor. If you do multiple single-zone systems, you are buying an outdoor unit for each. Much more expensive.

They quoted me a single outdoor unit (multizone) and then 2 high wall heads and 1 normal. After doing a little research, seems like the right approach. Thanks!

 

[PurdueSD]

Carrier/ Bryant is rebranding someone's mini splits -- find out who they partner with.

I'm surprised you can't get a better conventional system for the same price as the mini -- I can assume you don't have NG at the location?

The mini's do work very well -- how dirty is the area?

I'm not a huge high seer guy. I could get a higher seer conventional but the payback on my usage starts to approach the life of the unit. More parts and things to go wrong and this is just a garage shop. Ya no NG.

it's just a one man hot rod/ hobby shop. I keep my shop pretty clean but the dust does fly some. I imagine i'll have to be a little mindful of that when running any hvac. Do minis have a filter at all? My last shop was heated with a Hot Dawg and i had to clean it out once or twice in 6 years. Not really that big of a deal.

Should i be more concerned with dust going the mini approach?

 

[Trey T]

I wouldn't recommend mini-split for your shop.

I didn't even compare the heat/cool capacity of the two systems but always think of comfort first w/ air distribution, this is more critical. Generally, central air w/ ducting can provide better efficiency, in terms of comfort across a large space. You would need a lot of the mini-split wall units to property distribute across 40ft. W/ ducting, you can configure however you like to property distribute the air flow (see example below).

 

[yeldogt]

What's you electric rate?

It's not just about payback with the higher SEER .. they also have higher HSPF. How cold does it get? ... you need to have enough capacity when it gets very cold.

Did someone do a load calculation? My concern with the mini splits are the doors -- you would have to have the heads near the doors in the winter.

I love mini's I have a tri head in one house and I'm doing another tri my new build -- but they require a tight space to work as they are point source products.

 

[PurdueSD]

I wouldn't recommend mini-split for your shop.

I didn't even compare the heat/cool capacity of the two systems but always think of comfort first w/ air distribution, this is more critical. Generally, central air w/ ducting can provide better efficiency, in terms of comfort across a large space. You would need a lot of the mini-split wall units to property distribute across 40ft. W/ ducting, you can configure however you like to property distribute the air flow (see example below).

Thanks! Though if i go conventional it will be a spiral duct across the back 60' wall stepping down in size as it runs. Im not going to sacrifice ceiling height out in the middle for perfect distribution. Its just a shop and it doesn't have to be perfect.

HVAC is like voodoo. Ive been steered in just about every direction so far. I think its just so super regional that its hard to get a good read on the best approach. Maybe time to stop over thinking. But thats kinda what i do.

 

[Falcon67]

I have only a little experience with splits but for a shop that size I'd be pretty sure you'd need a quantity of ceiling fans to distribute the air around the space. My Samsung and LG "window shakers" will throw air 20'. The 24K split they use in the office at the drag strip throws a very short distance. Even in my smaller shop, I'd be concerned about moving air from a 24K split around the 24x28 section.

I am drawn the efficiency of the minis but in reality I'm not in there enough to benefit from that efficiency. When I AM in there, I want it cooling air ASAP. So moving air and capacity trump energy use. If I was retired and spent a lot of time in the shop, maybe different.

 

[PurdueSD]

What's you electric rate?

It's not just about payback with the higher SEER .. they also have higher HSPF. How cold does it get? ... you need to have enough capacity when it gets very cold.

Did someone do a load calculation? My concern with the mini splits are the doors -- you would have to have the heads near the doors in the winter.

I love mini's I have a tri head in one house and I'm doing another tri my new build -- but they require a tight space to work as they are point source products.

Electric rate is $0.113 per kwh dividing my actual bill up

Average yearly max low temp is 25, Average yearly max High is 88. We can see teens occasionally and zero a couple times in my life. We usually have some upper 90s every year and have seen 100+ occasionally. We live in a humid area.

 

[yeldogt]

What's the load calculation for the building? -- they do it at design temp at your location.

You need to make sure that the system can give you the heat. The AC is not a problem.

You have 3000 sf -- I don't think you have enough capacity. You can heat a foamed building with few openings at 1000sf per ton -- but it's got to be perfect.

I would do an electric -- propane comparison. I have both in my studio

 

[Trey T]

I have only a little experience with splits but for a shop that size I'd be pretty sure you'd need a quantity of ceiling fans to distribute the air around the space. My Samsung and LG "window shakers" will throw air 20'. The 24K split they use in the office at the drag strip throws a very short distance. Even in my smaller shop, I'd be concerned about moving air from a 24K split around the 24x28 section.

I am drawn the efficiency of the minis but in reality I'm not in there enough to benefit from that efficiency. When I AM in there, I want it cooling air ASAP. So moving air and capacity trump energy use. If I was retired and spent a lot of time in the shop, maybe different.

AGREED!! Here's my priority in a shop or home (at least in my region):

1. moving air (comfort)
2. property heating/cooling capacity
3. energy use

 

[theoldwizard1]

Now, getting back on track, if anybody could help:

Will (2) 2 ton Mini splits be able to evenly heat a 42'x60' shop?

Will they create enough airflow, or will i need fans?

Size, I hope your HVAC contractor can handle that calculation.

Fans, YES.

 

[theoldwizard1]

I'm not a huge high seer guy.

I think (not 100% sure) that part of the reason the mini-splits have such high SEER is the heat/cool is generated right where it is needed. Think about a central system where the heat/cool lost after pushing that air 30' ! It would also take a big (probably load) fan as opposed to some quiet ceiling fans.

Should i be more concerned with dust going the mini approach?

I would not.

 

[theoldwizard1]

Average yearly max low temp is 25, Average yearly max High is 88. We can see teens occasionally and zero a couple times in my life. We usually have some upper 90s every year and have seen 100+ occasionally. We live in a humid area.

This sounds like the perfect climate for a heat pump.

The real question is, when does the resistance heater turn on on the central unit. 25F ? 35F ? or 45F ? Yes, some kick on as high as 45F !

 

[PurdueSD]

This sounds like the perfect climate for a heat pump.

The real question is, when does the resistance heater turn on on the central unit. 25F ? 35F ? or 45F ? Yes, some kick on as high as 45F !

32 degrees

 

[PurdueSD]

Here is the heat loss calc i did a while back if it helps.

I did this when i was weighing whether to use the big glass doors or not.

 

[justinjoyal]

Why 5 tons of cooling with one option and 4 with the other ? The load remains the same..

 

[theoldwizard1]

32 degrees

So resistance heater will be getting a good work out from December through March. $$$

 

[PurdueSD]

So resistance heater will be getting a good work out from December through March. $$$

Nope, I have 5.5 tons heating my house- heat pump with electric backup. We usually get one month a year (January or February) where we see bills that are about $100 above average. Honestly im ok with it. We dont have the Michigan climate so we arent averageing anywhere near 5 months of sub 30 temps. $1-200 bucks a year to avoid another propane tank is fine by me.

Some people really buy into super high efficiency. Im not one of those people. If you really sit down and do the math... you aren't saving what you think you are over the life of a system. Its really hard to overcome that initial investment if you factor in where your money could be otherwise invested.

I am aware that some of my choices (i.e. big glass doors) aren't going to be the economical choice. I didn't choose them for economics.

I just want to spec an HVAC thats is going to work really well and make sense finanically. It doesnt have to have the absolute cheapest operational cost.

Gas is out, i'm between forced air and mini-split.

 

[yeldogt]

The higher efficiency equipment is not only about saving energy -- although the do save energy. It's about comfort ..... you can match the heat/ cool load needed at a given moment with the staged/ VS equipment ... and they do it silently. My Carrier HP system was running down to 0 degrees last winter matching all the way. It does not have or need a backup.

In some states the incentives make the more expensive equipment not much more.

 

[thymer]

I used a air sock in my 60x40x14, 5 ton heatpump with no backup heat. Keeps it plenty warm in the winter in SE virginia.

 

[Falcon67]

So resistance heater will be getting a good work out from December through March. $$$

Our house heat pump doesn't use the emergency heat strips unless it's really cold and damp, like 20s or so. That's real rare. Our old system had three elements of strip heat, 12.5 kW. We use WAY less power in winter. In summer, the use is about the same - 1660 sq/ft, 3.5 tons of air.

We are looking at replacing the Honeywell thermostat because it triggers the heat strips if the set point ends up more than 2 degrees off the ambient. I can't find any adjustment for that. In contrast, an Ecobee will wait as long as 2 hours and I think you can set it to never use emergency heat.

In the shop the 5kW resistance heater will run a bit until the space is where I want it, then it runs maybe 15 minutes/hr on cold days.

At any rate, resistance heater use can be managed such that it's not a killer.

 

[nsula_country]

MOST "central" heat pumps will kick on the heat strip when temps go below about 32F.

Disclaimer: I am a Heat Pump advocate if it will work in the site installation climate.

Depends... Heat Pump/Resistive Heat systems are customizable.

It is all in how you set up the control wiring and thermostat.

The resistive heat can be setup to ONLY come on when Emergency Heat is selected on thermostat. Not operate at all when in Heat Pump mode.

Resistive heat can be setup to ONLY come on when the Heat Pump needs to run defrost cycle to minimize cool air sandwich.

Resistive heat can be setup to ONLY come on when the Heat Pump needs to change temperature greater than the set on the thermostat for quicker temperature rise.

Resistive heat can be setup to work in tandem with heat pump if temperature is below the the setpoint on condensing unit sensor.

Also in any of the above configurations, IF thermostat has multiple stages the resistive heat can be set to operate 1, 2, or all elements. Giving more flexibility.

CT

 

[yeldogt]

I used a air sock in my 60x40x14, 5 ton heatpump with no backup heat. Keeps it plenty warm in the winter in SE virginia.

You are running under 500sf per ton -- I would hope it would work.

The Op is trying to do more sf with 3 ton in what looks to be a colder climate.

 

[PurdueSD]

You are running under 500sf per ton -- I would hope it would work.

The Op is trying to do more sf with 3 ton in what looks to be a colder climate.

No i'm not.. where did you come up with that ?

4 tons forced air vs

5 tons Mini split

 

[yeldogt]

No i'm not.. where did you come up with that ?

4 tons forced air vs

5 tons Mini split

I did read that wrong -- I missed that it was 2 X 2ton heads. Carrier does not make a full 5 ton .. it's 4.6. They partner with Toshiba (Toshiba makes a lot of rotary compressors)


I can't read the chart -- but the Toshiba compressors can normally work down to 10 and give full output. Thats still 600/T .. and the design ideal on the mini is 80%