Why Mini Split Heating Is Not Good for a Shop

It was time to build a shop for the business. At 61 year of age, I wanted to assure that this shop was everything I needed to complete my masculine mechanical life. The shop is 30ft x 50ft. It has a 12ft x 50ft lean-too, in which 12ft x12ft of the lean too is enclosed for a utility room which contains a toilet, sink, shower, washer, dryer and houses the air compressor.

I assured that the shop was equip with a 12k auto lift, multiple 240V outlets for welders and plasma cutters, around the inside of the shop as well as airline outlets every 10ft around the permitter of the building. All the air lines, water lines and electrical lines were run underground inside the concrete. The concrete is 8 inched in the middle with a 24inch x 24inch footer. 3/8" rebar was installed every 12 inches to reduce cracking.

The complete building had closed cell spray foam insulation installed. The closed cell insulation

was the full 2-1/2 inches on the walls and the ceiling. Note: the closed cell installation was very

messy. If the spray foam gets on anything the epoxy content will leave a round visible mark on

everything and anything it lands on. The washer and dryer had gotten foam over spray on the face

panels and glass door, the epoxy in the foam burned into the plastic and glass leaving small round

circles polluting the faces of the machines as well as the mower and air compressor. these were all

outside. The overspray came from the small open area where the walls meet the roof . Thankfully the cars were parked far away an not affected by the overspray. 

The Mini Split

When it came time to deciding on the HVAC, I had numerous people tell me that the mini split HVAC

was the way to go. I was told that they are quiet, very efficient and cost much less than a 2-ton HVAC.

I listened to them and started the process.

Calculated BTU needed was 28,000 BTU. I wanted to assure that the compressor was not going to

be over working so, I elected to install a 36,000 BTU unit and complement the package with four air

handlers to keep air circulating nicely. I installed the compressor on cool shaded side of the shop. off

the ground about 4 feet for additional air circulation. Some will say that I have the air handlers too far

away from the compressor. The manufacture stated that I can have two lines at a maximum of 50ft.

I have one (1) 48ft line, one (1) 30ft line and two (2) 25ft lines. I have had the freon pressure checked,

and it is full to specs. I have used a laser thermometer to assure that the air handlers are blowing the

correct designated temperature, which they are. 

The first 28° cold day

When I entered the shop I was surprised that the geothermic's were keeping the inside of the shop at a cool 55°. The sun was just cresting the horizon, so I knew that the sun didn't have influence on the inside temperature. I started up the Mini Split up and set all the air handlers to 72°. To my vast disappointment, after two hors the shop only heated up to 58°. It took over four hours to heat to 72°. WOW! what a disappointment.

WHY?

Internet research enlightened me. I just learned to never listen to friend's. I discovered that a Mini Split is not like a large 2 ton HVAC unit in the terms of "start up heating". When a large 2-ton HVAC unit start ups, it engages additional heating coils. The temperature of the air coming out of a 2-ton central air unit is, 120°-140°. After the room reaches within 3°-4° of the set temperature, the central air unit adjusts the air temperature approximately 3°-7° above the desired setting. When a bay door is opened and heat lost, the full size HVAC goes back to heating at 120° to 140°.

When a Mini Split HVAC unit starts up, it will only heat up 10° above (10°below if the A/C is on) the desired setting. With this applied, it will take a Mini Split a considerable time longer to heat your shop back up to the desired temperature.

This in turn relates operation to; If its cold out, every time you open the bay door to pull a vehicle or equipment into the shop, the majority of the 72° warm air will be lost and it will take an additional two hours to warm the shop back to the desired temperature because, the Mini Split air temperature will only be distributed at 82° rather than the 140° air from a full size HVAC. You would be correct if your thought process lead you to understand that you will consume a lot more energy ($$$) with a full size HVAC than with a Mini Split. Mini Splits cost efficiency comes at the additional cost of quick gratification of a warm shop.

If I had to do it all over again, I would definitely NOT install a Mini Split, I would install full-size 2-ton HVAC unit. I'm not in the garage that often and when I'm the bay doors are typically opened and closed a good number of times. If I used my shop for wood working, I would probably use a Mimi Split because I'd leave the unit on 24 hours.

If you have any questions, feel free to call. 931-292-0145

I hope this helps.

Good luck and be safe.

Mike 

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