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nokiasixteth 01-22-14 08:06 PM

sizeing a mini split
 
I had originally wanted to get a mini split . But the more i look at mini splits the more im thinkin on just getting one of those. If the geothermal had some that was ductless as well i would prob lean toward it . But right now i am heating with space heaters alone . Theyve been eating up some electricity lately with these oddly cold days weve been having here
Not being really familiar with min splits ive been thinking on a 1 ton mini for my main living space and later on another for the other part of the place we rarely go into .
The whole house is around 1050sq ft so i may be a bit over kill. Fixing to add another R15 to the attic and insulate the outside walls wich has no insulation.
Any one have any good suggestions that theyve had with minis. Main that we stay in is 556 other part is 418 and the wash room is 80 sq ft but it stays shut up most of the time.
Found 2 mini splits 1 is 15 eer 623 and the other is 1130 both are plus freight.
Would it be worth it to fork out the extra cash on the 5 extra eer. Or would that play much of a difference

AC_Hacker 01-22-14 09:01 PM

Quote:

Originally Posted by nokiasixteth (Post 35024)
Main that we stay in is 556 other part is 418 and the wash room is 80 sq ft but it stays shut up most of the time.
Found 2 mini splits 1 is 15 eer 623 and the other is 1130 both are plus freight.
Would it be worth it to fork out the extra cash on the 5 extra eer. Or would that play much of a difference

You are talking about needing a mini-split for heating, but in MS, you'll probably need A/C more.

But let's just say you were only concerned with heating. The most important measure of a mini-split performance for heating is the Heating Season Performance Factor, or HSPF. A lot of the sales people will not know anything about this, but it is a specification that is required by the US Government to be available so that you can make the right choice. If you tell them that you will not buy any mini-split that does not have the HSPF, they will suddenly be able to find it. The higher the SHPF, the less electricity you will need to use for heat.

If you were going to use your mini-split more for cooling than for heat, you would want to know what the SEER is. The higher the SEER, the less electricity you will need to use for cooling.

A unit with a high SEER doesn't always have the highest HSPF, so it's good to know both.

Next to consider is how much do you think you will be running your unit? If you will be running it a lot for cooling, then it will be to your advantage to get the one with the highest SEER. If you will be running it a lot for heating, then it will be to your advantage to get the one with the highest HSPF.

If you don't think you will be running it very often, then a lower performer would probably be just fine.

I did a mathematical calculation on this very thing for my shop which needs heating, but I don't use my shop very often. So in my particular case, a lower performing unit would be way better than an electric room heater and would pay for itself pretty quickly. But if I was in my shop all the time, then it would be worthwhile getting a high performance unit in the long run.

I lived a while in MS so I'd imagine that your heating season will predominate. If you have some good shade around your house, and good insulation, you might be better off with a lower performer which is a cheaper unit.

So it all depends on your house.

Also, what brand it is matters. They're all made in China, but different brands are built to different specs. We have heard very good things about Sanyo, Fujitsu, Mitsubishi. I have nothing to say, either good or bad, about the Chinese brands. We just haven't heard very much about them, long term.

(My own personal opinion on the matter is to get the highest performer you can afford, I doubt that you'll regret it.)

Best,

-AC

nokiasixteth 01-26-14 12:17 PM

Well at the moment ive got decently efficient window unit that i use 8000 btu. It does good for where i stay. I dont heat and cool the whole house because of the money it cost. I am heating with just a space heater. Radiator heater. Ran a Kil o watt meter and divided the time it ran 650 watts a hour what its usin at 68 and 70. Figured if a heat pump is more efficient have the cop of 3 . Wouldnt that mean rough estimate 215 to heat the same ? There for i could heat 3 more rooms the same size for the price im heating only 1 3 more rooms would be almost the whole part we go through durin the day. .
Or am i just way off on the figures.

jeff5may 01-26-14 02:55 PM

To answer your question, an air source mini split will level your heating and cooling bills.

Without improving your home at all regarding energy efficiency or leakage, a 3/4 ton unit will do a little more cooling than your window shaker a/c unit. How much less it costs to run depends on the unit. A window unit usually comes in around 10 SEER or less on the energy scale, so a higher SEER mini-split will either run less often (saving money) or cool more of your home (for the same price).

During heating season, you can predict how low the unit will go regarding outdoor temperature by relating to the current window a/c unit's summer performance. For example, if the current unit does a good job up to 98 degF during the summer, the mini-split will do roughly the same at heating down to around 38 degF, asuuming a setpoint of 68-70 degF. Below this temperature, a "cheaper" constant-speed outdoor unit will begin to drop off and may not satisfy your heating demands. A variable-speed "inverter" unit may or may not keep up with demand, even if its heating capacity does not drop off. Depending on the home, the heat may leak out faster than you can afford to supply it. A larger unit may or may not be necessary to avoid using backup heating.

Right now is the best time of year to do your own site survey. Shut the house up tight and turn on an exhaust fan (bathroom, range hood, etc.). Light up a stick of incense and start checking windows and doors first. If you have a large leak, you won't need incense to find it: the cold airflow will be obvious. Rooms that are colder than the rest of the house (unless kept that way) are that way because they are leaking heat. And that heat costs money.

nokiasixteth 01-27-14 05:42 PM

Yeah .I plan on switchin to double pain windows and tearin out the walls putting in insulation. Been thinkin just puttin in the blow in . Its cheapest. But a buddy of mine mentioned the spray foam insulation may be a bit better.

MN Renovator 01-27-14 09:53 PM

Hattiesburg, MS appears to be close to your place so I'm using the numbers that I found for Hattiesburg figuring it is close to you. Heating design temp is 27 degrees and cooling design temp is 94.

I'm assuming you are looking at the space heater running at about 45% of the time based on your kill-a-watt reading? What temperature was it outside when you measured this? When trying to size a heat load you usually want to go off of a day as close to your heating design temp as possible and you can extrapolate a little bit from that point. If you had a single 1500 watt space heater doing the job you could go with a 9000BTUhr mini-split to cover that load and it would have almost twice the heating power of your 1500 watt space heater. 27 degrees outside is not really a challenge for a heat pump, especially an inverter heat pump. If you are happy with the performance of the window unit

"During heating season, you can predict how low the unit will go regarding outdoor temperature by relating to the current window a/c unit's summer performance. For example, if the current unit does a good job up to 98 degF during the summer, the mini-split will do roughly the same at heating down to around 38 degF."

How do you figure this? In the summer most of the cooling load comes from the sun shining through the windows and in the winter the heat loss is through the glass, walls, ceiling, and floor. The heating requirements will be a lower BTU than the cooling requirements per degree. For example if it is 88 outside and my house is at 75 on a day with full sun, my house needs 15000BTUhr to hold 75 degrees. ...but in the winter 15000BTUhr of heat will take care of me at -2f if I keep it 68 degrees inside.

To put it simply, the heat pump manufacture will usually have a balance point chart showing the outdoor temperature and how much output it will provide at that temperature. If you are working just fine off of a 1500 watt space heater(5000 BTUhr roughly), a 9000BTUhr heat pump should be able to provide at least that much heat at your design temp. The AHRI Certification Directory site under 'variable-speed mini-split and multi-split heat pumps' will show you the output at 17 degrees, pretty much every heat pump will exceed a space heater with that kind of outdoor temperature.

The higher the HSPF, the lower the energy it will use to heat the winter. The higher the SEER, the less energy it will use to cool in the summer.

For a 1050 square foot house, if the 9000BTUhr mini-split turns out to be inadequate, my suggestion would be to seal up the place better first, then add more insulation.

If you are really planning to put two in the house, I wouldn't go with anything bigger than 9000BTUhr because 18000BTUhr will be more than plenty for the whole house in the winter.

I don't know your summer cooling load though, that is harder to calculate and isn't just a matter of how much insulation is in the walls, windows, shading, which direction the windows face, etc are large factors and the Manual J cooling load calculation is a bit complicated for that. If your 8000BTUhr window AC can't do the job with all of the doors open in the house, you'll need to go bigger for cooling, add a good exterior shade cloth or other shading to the outside, or otherwise block more sun to get the load in a good place.

nokiasixteth 01-27-14 10:19 PM

The days that i did them test it was abnormally cold for this area . I believe it was down in the teens. I will do another one to get a new test Yeah. Its a older house durin the summer . I averaged about 10.5 kws a day. With the Air conditioner on the south wall in the boilin sun and the attic without insulation at all then. I doubt that it could have don the job with a door or window open then.
For it to get down in the 20s here its a bad cold day

nokiasixteth 01-27-14 10:31 PM

http://www.kozykool.com/wp-content/u...er-12-36-2.pdf

12HRDN1 Has anyone had any dealings with kozykool ?

nokiasixteth 01-27-14 10:46 PM

Figured tonight would be good enough night to do the test as any. Supposed to be cold here. 30 the high and 18 the low. Right now its 42 got the radiator heater set to 68 degrees. The low for tonight 27.

MN Renovator 01-28-14 07:07 AM

"I doubt that it could have don the job with a door or window open then."

Just to clarify, I'm talking about doors inside the house, definitely not a door or window facing the outside.


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