Mini-split sizing

bubbawatson · December 17, 2015, 06:20:42 PM

Hi folks, I am building a small ish (big for us!) home in rural GA and am looking for some advice on hvac. I have installed a mini split before in a garage, which was fairly simple and worked well, and we are trying to do as much as possible ourselves, so I like the idea of them.

Hence, I am thinking of using a multi zone ductless mini split for this home. It will be carriage house style, with a garage and 2 bd/2ba living space on 2nd floor. Around 900sf. Does anyone have any input on how well they work for multiple spaces, especially in our mostly hot/humid climate? Should I put one in each bedroom (plus the living)? Help appreciated!

Redoverfarm · December 17, 2015, 07:10:03 PM

Quote from: bubbawatson on December 17, 2015, 06:20:42 PM
Hi folks, I am building a small ish (big for us!) home in rural GA and am looking for some advice on hvac. I have installed a mini split before in a garage, which was fairly simple and worked well, and we are trying to do as much as possible ourselves, so I like the idea of them.

Hence, I am thinking of using a multi zone ductless mini split for this home. It will be carriage house style, with a garage and 2 bd/2ba living space on 2nd floor. Around 900sf. Does anyone have any input on how well they work for multiple spaces, especially in our mostly hot/humid climate? Should I put one in each bedroom (plus the living)? Help appreciated!

Here is where I purchased mine. The best prices I could find. Free shipping and no sales tax. They also sale all of the lines and wiring associated if you know the length of lines they are sold in "Line sets". You will have to supply the drain lines but that is just standard PVC. They sell more than one brand but I stayed with Mitsubishi which I believe originally developed the system. There is so many possibilities with Mini-Splits with various size outside units and inside units BTU's and types. Due to the room configuration I went with two floor units(9,000) and two wall units (12,000)for a total of four and a 3 ton outside unit. One nice feature unlike a ducted system is that you can operate each air handler independent of the others.

https://www.younits.com/ductless-mini-split/complete-ductless-systems.html

The sales person I dealt with was Paul. His number is 1-800-880-0199. I am sure if you give him a call and furnish the layout and sf he will help you with the sizing. He appears to be very knowledgeable and I believed he has worked in the HVAC field.

If you have not enclosed the walls then you can easily run the lines and drains in the partitions and eliminate the outside exposed wiring and refrigerant lines. I put most of mine on one wall on two different floors and was able to route 4 units into two drains and utilize the same chases. I sort of went in the back door figuring mine. I had a HVAC company to give me estimates and they did the sizing. When they advised the installation cost I about went through the roof. I had the sizes they estimated that I needed and I went on the hunt for the same equipment for about 1/2 of their cost and self installed the system. I did have a friend in the HVAC to make the final connections as far as purging the lines and shorting them to the proper length to hook up to the outside unit. The refrigerant is self stored in the unit for the system.

Good luck. Anything I can help you with just drop me a message.

John

December 18, 2015, 07:00:09 AM

I installed two Mitsubishi HyperHeat units in our 1400 square foot ICF house in upstate SC. They work great and are super quiet and cheap to run. One 12K unit actually does our entire house most of the time. Ours are the basic wall-hung units.

I recommend using an HVAC calculator program. I used HVACCalc, which was $50 for a 45 day usage. With any program, the key is to be thorough and honest with all of the values you input. It's important to determine what your actual HVAC load is. I had a 'professional' tell me I needed a 3 ton central unit, which would have been WAY to big, and wouldn't have worked well or efficiently. As John said, let me know if I can be any more help!

Jay

bubbawatson · December 18, 2015, 03:33:46 PM

Good info, thanks to both of you! I am thinking of doing a 3.5ton unit with 6+6+15+15 handlers. Two smalls for bedrooms, one big for living/kitchen area, and one big to throw in the garage. It's just going to be a workshop but it would be nice to have the option to condition it if I need. That might be overkill, I need to check out the hvac calc.

Any thoughts on LG? I am planning on Mitsubishi, as those seem proven and work well, but for the same cost LG has a 22 seer unit (vs 18 on the Mitsu). I don't know if that is fluff or not. I'll take longevity over efficiency if LG's reliability is not up to par

MushCreek · December 19, 2015, 07:14:06 AM

3.5 tons for 900 square feet?!? I use 1 ton for 1400 square feet. My summer cooling load is only 3/4 ton. I strongly recommend you find a program and run some numbers before designing your system.

I bought my units on-line for about $1600 each, including refrigeration lines and wall brackets for the outdoor unit. One caveat: Most manufacturers won't honor their warranty unless it is installed by a licensed contractor.

December 19, 2015, 09:29:40 AM

In process of getting a Fujitsu 24RLXFW (22KBtu cooling) (27.6KBtu heating), 18.0 SEER for my 1100 sf basement. Never gets below 60 in coldest of winter but now that we have grandchildren we need it warmer for them to play. Fujitsu warranty 7 yr compressor and 5 yr parts, installed price of $2600.00, hopeful to install next week or after Christmas.

Dave Sparks · December 19, 2015, 07:25:43 PM

There is BTW a completely different strategy for using a mini-split in an Offgrid like environment than HVAC people know about.
Any interest and I will expound.
The Fujitsu are close and above 30 SEER. One has to know the exact model as each company has many models. The best are what you want unless you do not care about energy consumption.

Tickhill · December 20, 2015, 07:44:40 AM

Please lay it out Dave, I am interested, for my next (last) home I build.

Dave Sparks · December 21, 2015, 10:44:49 AM

OK, I worked with Sanyo on doing this for offgrid. They were the first in the US 8 years ago or so. We had just had a major wildfire go over us and I needed to figure a way to stay inside and cool with something better than a window AC.

It seemed intuitive to me that the inverter based splits were variable speed and something that could control the speed should control the power.

It turned out that setting the differential from actual room to programmed to zero degrees would cause the split to run at minimum power (300 to 400 watts). Setting the differential to 2 degrees would use about 600 watts and 4 degrees about 1000 watts on a 12,000 btu/1 ton unit. As the room gets to the programmed temp the unit draws less power. The numbers above are an example.

With an open floor plan in the home and a free source of power, a much smaller than required split can run from dawn till dusk and the room never gains heat for cooling. Using too big of a split could be be a problem when there are clouds. I use the 1 ton in all my homes for my solar clients. If they want more I use a second 1 ton. The combo units are not the highest SEER and you do not get the redundancy. The second unit really only allows you to cool down the room faster. It is no better than one unit that has run all day.

The solar for an offgrid home needs to be either virtual tracked or azimuth tracked to get dawn to dusk electricity for the split when cooling.

Heating with a split offgrid is harder to do with winter weather and either propane or wood burning is the primary. The split will reduce the wood or propane use significantly and is the perfect use of solar in winter after the battery has charged.

The Fujitsu 1 ton is the state of the art now for cooling at 30 SEER. It is an amazing heater at close to 5 / 1 compared with resistance heating.
There are many ways to use a split with different house layouts and regions where it does not cool down at night offgrid. I think I have done them all now. I am working now on a way to automate the energy use to always keep the battery full when clouds are about. This is not as much of a problem with cooling and more of an issue with winter heating.

December 21, 2015, 10:58:16 AM

Thanks Dave

MushCreek · December 22, 2015, 07:48:42 AM

One problem I ran into is that they didn't make small enough mini-splits for a super-insulated space. We have two Mits HyperHeats, a 12K and a 9K. The 12K does fine for the whole house, so we only run the 9K in the master bedroom if it is very cold. The actual size needed for the master suite is only about 4K. Both units seem pretty efficient, and short-cycling hasn't been a problem, but it would be nice if much smaller units were available.

Our house is ICF, and so very temperature stable. I've never heard our minis run on any speed but 'low'. This year, we haven't had our heat on yet. It's been a very warm fall, but Saturday AM it was 22 F. outside, and 64 F. inside. Gotta love thermal mass!

Tickhill · December 22, 2015, 03:40:48 PM

Thanks for the info Dave, bookmarked for future reference.

mattjsparacio · February 21, 2016, 06:16:30 PM

In an off-grid situation, could a mini split be set up as a dump load? Only running when the batteries are charged?

Dave Sparks · February 21, 2016, 07:36:06 PM

A heat pump is the absolute best use of opportunity energy use or self consumption offgrid.
Cooling, heating, domestic hot water are amost always backed up offgrid. Once the battery is close to full, on many days, there is a tremendous amount of unused energy in a home that is designed for capturing/harvesting energy in winter.

February 22, 2016, 05:36:31 AM

Just a follow up on my mini split install, a couple of weeks after install we had a low of 16 one morning and it was 76 in my basement. I am impressed and I know it will see minimal use during the summer. I will let you know impact on my power bill.

Dave Sparks · February 24, 2016, 11:43:53 AM

What make/model did you buy please? I am working/almost done on an app that will control the split based on Battery voltage for grid tie and offgrid battery based solar applications.

Tickhill · February 24, 2016, 11:06:20 PM

Fujitsu
Inside Unit: ASU24RLF
Outside Unit: KTA034682

24,000 BTU
Warranty: 7 year compressor 5 year parts

Dealer used Fujitsu website for sizing, 1100 sqft basement, south walk out

Adam Roby · February 25, 2016, 06:46:44 AM

Funny how they can still call it "mini" at 24,000 BTU!

Sounds like an awfully big unit. I think ours was a 12,000 BTU Mitsubishi for a 1500 sqft open concept house at the time. Took a bit of time to cool the entire house but once at the right temperature it maintained it fairly well.

Dave Sparks · February 26, 2016, 03:24:39 PM

With the grid most people want to cool down a hot room quick.
This is not what we do offgrid but as you said Adam once it is cool, a 12,000 btu or 1 ton will do fine.
I use 1 ton in all my clients homes and add a second one as a spare sometimes if they can afford it.
The 3/4, 1.0 & 1.5 from Fujitsu are state of the art now. You must know the exact model as there are many models with different specs.

Tickhill · February 29, 2016, 06:38:12 AM

To get full warranty, we had to go with unit recommended from Fujitsu, based upon type and size of space being conditioned, geographical location. Our biggest concern was warming a cool to cold space to a comfortable level for the grandchildren. We are pleased so far.
Feel quite confidant that we will use Fujitsu or Mitsubishi mini splits for our next and hopefully last home, in the future.

February 29, 2016, 03:57:46 PM

Warranty is a nice thing but sadly many of my remote homes have to work around that.
The good news is the standard mini-split comes with a 5 year warranty because it is built so well.
If the person who installs it has basic HVAC knowledge they are a snap! not to mention the price difference.

NathanS · March 01, 2016, 09:33:23 AM

Some of those mini-splits are rated down to -15F. I have seen some of the more insulated new construction houses are being outfitted with them even in the North East, and Canada.

I am really interested in this, as it seems inexpensive and relatively simple to install. Our main heat source will be wood, but I am pretty sure NYS law requires the 'main' heat source to be set by thermostat. I really don't want to go down the road of oil/propane furnace.. very expensive and will sit almost entirely unused.

Dave Sparks · March 01, 2016, 11:46:20 AM

We use to burn 2 cords of Oak in the winter 10 years ago. In 2007 we dropped our usage to one cord with the mini split.
With more solar, the past few years we are down to less than 1/2 a cord. We even have an electric oven for good solar days when we bake for free instead of burning propane. The mini-split was a game changer for us and it is now in all my designs for offgrid.

In NYS you will need (one heat source must be traditional) a propane or? furnace and maybe one in a bedroom to meet code, if it is inspected.
These can fairly be small wall/floor units that do not have ducting other than a 5 inch hole in the wall for intake/exhaust. Ours are covered up on the outside and the inside has a nice wood cabinet. It was used one time and it was the cost to be legal.

NathanS · March 01, 2016, 02:40:42 PM

Quote from: Dave Sparks on March 01, 2016, 11:46:20 AM
We use to burn 2 cords of Oak in the winter 10 years ago. In 2007 we dropped our usage to one cord with the mini split.
With more solar, the past few years we are down to less than 1/2 a cord. We even have an electric oven for good solar days when we bake for free instead of burning propane. The mini-split was a game changer for us and it is now in all my designs for offgrid.

In NYS you will need (one heat source must be traditional) a propane or? furnace and maybe one in a bedroom to meet code, if it is inspected.
These can fairly be small wall/floor units that do not have ducting other than a 5 inch hole in the wall for intake/exhaust. Ours are covered up on the outside and the inside has a nice wood cabinet. It was used one time and it was the cost to be legal.

That is awesome Dave. We will be on the grid and everything is going to be inspected.

The heart of the house will be a modern airtight wood cookstove. Will be interesting to see what the inspector says. Cookstoves are EPA exempt, and they should be used to dealing with the Amish, so hopefully it won't be too much of a headache.

Are you saying you installed a small propane furnace to pass inspection? I want to keep things as affordable as possible, as we will already be investing a lot of money on the cookstove and chimney pipe. I am not above putting in electric floorboards to avoid being criminally charged.

Redoverfarm · March 01, 2016, 05:25:53 PM

Quote from: NathanS on March 01, 2016, 02:40:42 PM

The heart of the house will be a modern airtight wood cookstove. Will be interesting to see what the inspector says. Cookstoves are EPA exempt, and they should be used to dealing with the Amish, so hopefully it won't be too much of a headache.

Are you saying you installed a small propane furnace to pass inspection? I want to keep things as affordable as possible, as we will already be investing a lot of money on the cookstove and chimney pipe. I am not above putting in electric floorboards to avoid being criminally charged.

On the East coast most insurance companies will not cover a residence unless there is some other type of heat besides wood. Not sure what their reasoning is other than water lines will freeze if the wood heat is left unattended. But in the same reasoning there is several and I mean several outside wood fired boilers or furnaces that convert the heat to either hot water baseboard or forced air. They apparently are covered.

I had even heard that one gentleman bought a house, installed a wood stove and removed the furnace. Now he is trying to sell the house and has to install a more permanent heat source before lenders will loan money for the new owners. He is putting electric baseboards in. I guess if the house sells the new owner can remove the baseboards and go primarily wood. But they should store the baseboards I guess.