"A/C only" mini split?

[chrispyny]

I want to add a/c to my 1971 raised ranch. Currently window shakers. I'm very mechanically inclined and do all but the most challanging projects myself. After reading countless hours of threads here on gj, and then countless hours on ecomfort (by far easiest to follow web site for minisplits) i have decided to go 'a/c only' rather than heat pump, and i want you all to confirm my intent.

Bought my house in the spring of 2012. 1400 sq ft raised ranch, 2x4 construction, windows 25 years old. For HEAT, I currently have hot water baseboard hydronic heat with a 46 year old natural gas National hot water boiler supplying the hot water Located in the garage. I want to replace it but its super simple and won't quit on me. Fall of 2013 i replaced the overpressure valve as it was leaking and the expansion tank as the bladder failed, so pressure was rising in the system to unsafe levels.
As a back up heat source i have a gorgeous and very efficient Jotul c450 wood stove insert installed in the fireplace in the spring of 2013. I also have 8-10 cords of seasoned split oak/maple/hardwood mix stacked and ready to burn at a moments notice. It can heat the house entirely as long as a run a box fan in the far hall where the bedrooms are.
I mention all this as i see NO need to purchase a minisplit with heating capabilities as heat from the minisplit would never be used.

I currently have a 10k btu window shaker for the dining/living room on the left side of the house on the second floor. Nothin for the den on the left side of the house on the first floor. The 10k window shaker is VERY loud and heavy and drowns out normal comversations in the entire living area (again dining/living room). It also really struggles to cool the space and never cycles off except during its built in defrost cycle.
In the downstairs den/man cave where i spend most of my time, it gets hot and sticky in the summer and i rely on the very little bit of cooled air from the 10k window shaker to splill down the stairs from upstairs for cooling.
Last spring i installed foil radiant barrier in the attic and it helped tremendously on the main second floor, and i have plans and money set aside for a new roof, adding attic ventilation in the form of ridge vent, and blow in insulation all for this early spring. Regardless, I NEED something different. I can't take the noise and install/uninstall process every season.

I use more window shakers for bedrooms but that is a non-issue as they are small and quiet enough for now.
To my point, here is the system i chose. http://www.ecomfort.com/Panasonic-CU-4KS24-CS-MKS7-18NKU/p56202.html

I chose this as im bumping the btu's upstairs from a struggling 10k to 18, and getting 7k btu's downstairs for the den and adjacent bathroom. I feel that although i'll be adding venting in the attic and insulating from a barely r11 in the form of rolled 4" pink insulation to blowing in another 20" of pink fiberglass, i think the 18k in the living/dining room will be properly balanced to both cool very well and still cycle long enough to pull moisture out of the air and dehumidify perfectly. As for downstairs, i could probably get away with a 5k btu unit but there doesn't seem to be one below 7500. It should be fine as it's not that much overkill. Also this package has the 24nbu comdensing unit rather than the 19nbu which will ensure the condensing unit can handle the heat load when running both wall units at the same time during thr hottest timed of the year. In upstate NY, it's not uncommon to reach high 90's for long stretches of time.

Am i nuts going with cooling only? I need critisicm. Let me know what you all think of my plans please!

 

[rlitman]

Yes. I LOVE my mini-split. It cools my entire downstairs, in a way that could never be done with "window shakers". And it does it quietly, with great efficiency.

But saving a few bucks to go cooling only was the biggest mistake I made in that install. Looking at the heating efficiency numbers, using it to supplement my heating would have easily helped make it pay for itself, even though I'm in an area with some of the most expensive electricity in the country.

 

[priesttherunner]

I think it is based on your desires.

Do you want to control upstairs/downstairs independently? If not then just put your intake duct in the downstairs and the house will self-rotate.

Also, look at air capacity and CFM rates. A rookie mistake in HVAC is to simply consider if the ability to heat/cool is there without looking at the ability to transfer the air.

Where are you putting the unit? Floor vent on the second floor and ceiling vents on the bottom floor is the simplest method IMO.

(Engineering design technology A.A.S. with experience in HVAC system design).



Edit: I think if the pricing is close enough, then go with a mini-split and not AC/only. Even if you don't use it, it can add a little resale value and as rlitman said you can depend on it as a supplement if desired.

Any way you could run a filtered blower system past or from the wood burning stove into the vents? That is an extremely efficient system as well.

 

[chrispyny]

Both wall units will be mounted on the wall, just one above the other, for thier respective rooms. . If looking at the house, electric phone, and cable come off the street to the left side of the house. Running electric to the outside of the wall will be elementary for the comdemsing unit, which will be ground mounted.
18k unit will be mounted on the same wall upstairs, (right between living and dining room) and directly below it by several feet, the 7500k bru unit will be mounted on that same wall but downstairs ( in the middle of the den ).. Placement will be perfect for both units in regards to ease of install, proper air circulation, and appearance.
Hey priesttherummer, you see i'm talking about mini splits right? No such thing as intake ducts or cfm rates per se with Minisplits.
Anywho, I need more btu's upstairs, i need cooling downstairs, i need quiet cooling, with my house, ductless minisplits are THE answer. I just can't see why i'd want a heat pump rather than my plan of a/c only.

 

[rlitman]

Like I said, the difference in price for the heat option is small, and the heating from them is pretty much the cheapest source of heat you can get (at least, when it's above around 20F outside). The heat really doesn't have a down-side to it.

 

[priesttherunner]

Ya.

Didn't know you were going with exposed and two units, my bad. Either way, I would say that if the price is manageable, go ahead and add the heat option. It might be nice for those short periods where you need heat but don't want to get a wood burning stove up to full run. Heat for a few hours and shut off as needed.

If you went with only one unit and did the hidden version, you could circulate air by facing the intake downward (into the first floor) and the output upward (into a floor vent of the first floor). If you are going with two units then you might as well do exposed wall mounted though.

 

[priesttherunner]

Another example:

 

[pseudorealityx]

Where the heat pump option shines is in the shoulder months, when you're just trying to take the edge off. When it's 50-55 degrees outside in the spring and fall, or it gets chilly at night. You just set the thermostat and it does what it needs to do, and no more thought needed.

 

[Git]

When I first started looking at mini splits, I was of the same mindset - AC only, especially since i live in S Cal

But, I ended up with the heat pump and I am VERY glad I did..

As I recall, the price difference was not that great and my thoughts were I was only going to do this once with a mini split-I had already been down that road with a through the wall unit

Go for it - and why not have eComfort spec you out a system?

 

[Jinks]

I didn't see any mention of "inverter" compressor on that unit you have selected. If it has inverter technology & I missed it my apologies. If not, the only change I'd make to your plans is to look into units with the inverter compressors. My Mitsubishi has inverter tech. & is scary quiet both inside & out. It runs continuously, but at just enough speed to maintain the selected temp. Saves a lot of money & keeps temps steady.

 

[rlitman]

I didn't see any mention of "inverter" compressor on that unit you have selected. If it has inverter technology & I missed it my apologies. If not, the only change I'd make to your plans is to look into units with the inverter compressors. My Mitsubishi has inverter tech. & is scary quiet both inside & out. It runs continuously, but at just enough speed to maintain the selected temp. Saves a lot of money & keeps temps steady.

+1
My Freidrich (which I later discovered is made by Fujitsu) is also inverter driven. It can be amazingly quiet. For the most part, no more noisy than a ceiling fan,

 

[chrispyny]

I didn't see any mention of "inverter" compressor on that unit you have selected. If it has inverter technology & I missed it my apologies. If not, the only change I'd make to your plans is to look into units with the inverter compressors. My Mitsubishi has inverter tech. & is scary quiet both inside & out. It runs continuously, but at just enough speed to maintain the selected temp. Saves a lot of money & keeps temps steady.

Gosh, i honestly just assumed since this is a panasonic unit and what i can tell up there with the high end ones, i assumed it was inverter technology?
I'll tell ya one thing, at that cost, it better be or i'm going with something else. Frankly those wall mount units aren't exactly the prettiest units i've seen. Not a big fan of the multiple thin fins. I've seen far better in person from other manufacturers.
Thanks guys, i'll look into this.
Google searched and found this site.. http://datasheets.globalspec.com/ds/3437/PanasonicHVAC/6C4F29CD-27EF-486B-96B2-73196F1BAC1F
From that site..
Cu-4ks24nbu
Panasonic Flexi Multi wall mounted air conditioners offer the utmost in versatility in solving your cooling and heating needs. By utilizing environmentally friendly R-410a refrigerant and DC Inverter technology, the Panasonic Flexi Multi wall mounted air conditioner, automatically adjusts its performance to meet the changing needs of the space while maintaining the desired temperature. This leads to increased efficiencies, low energy consumption and a very comfortable environment.

 

[bzinsky]

was in a similar scenario recenty deciding how to cool some office space. Took me all of 15 seconds to determine the heat pump was the best option.

Easy way to fix any zone issues, its essentially adds a new zone for you. Most importantly is backup heat. When most people lose their heating system it is an emergency. Even worse is if you are not home and you lose heat in the dead of winter. Few hundred bucks seems worth it just for peace of mind. Your main heater goes out you have plenty of time to diagnose and find parts, something that is important if you are just a handy guy and not in the hvac trade.

 

[theoldwizard1]

Like I said, the difference in price for the heat option is small, and the heating from them is pretty much the cheapest source of heat you can get (at least, when it's above around 20F outside). The heat really doesn't have a down-side to it.

CONCUR ! The only place I would recommend "A/C only" mini-splits is in the the SW dessert or far Southern FL. Even those places get chilly some mornings !

The cross over point (from heat pump to your current heating solution) may be more like 40-50F, but is actually more cost effective than you gas fired boiler.

 

[theoldwizard1]

I use more window shakers for bedrooms but that is a non-issue as they are small and quiet enough for now.

For now !

Plan for the future ! Is it feasible to run piping to those bedrooms either outside or inside the house ? If yes, you may want to buy a larger compressor unit that has 4 or 5 ports, even if you don't install the piping and air handling units for a year or two.

 

[david86camaro]

Over all most of the advice here has been pretty good. I'm a design engineer, designing HVAC systems, I do mostly commercial systems, but I deal a variety of types of jobs and systems. I think overall this will be much better than window shakers. My main input would be that I would have the heat option.
The main difference is a reversing valve and some extra controls, especially since you will have 2 units on one outdoor unit, it could help balance the upper and lower floors in the shoulder seasons without even running the outdoor unit.
The other thing is to make sure you are looking at the btuh output, not just the input, that my not be a big difference. Here in Colorado it is a decent difference because of altitude among other inefficiencies. With this being said my gut feeling is that you units maybe a little undersized, which wouldn't be a bad thing, it makes everything more efficient, but on the hot days in the summer the the system will struggle, but with that understanding it should be fine.


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[Jackfre]

I would think that with a 25 yr old boiler that you would want some back-up heat. That reason alone is enough to spend the additional dough for the heat pumps. As pointed out, by running the heat pump in the shoulder seasons you will be taking some of the stress off your old boiler.

 

[theoldwizard1]

I'm a design engineer, designing HVAC systems, I do mostly commercial systems, ... My main input would be that I would have the heat option.
.
.
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The main difference is a reversing valve and some extra controls, ...

On an installation like this, where there is a good running heat plant already installed, is there any simple way a homeowner can know when to switch from (electric) heat pump heating to (gas) boiler operation ?

I know cost of the energy is a big factor, but I am thinking some kind of SWAG/rule-of-thumb say +/- 10-15 degrees.

 

[priesttherunner]

On an installation like this, where there is a good running heat plant already installed, is there any simple way a homeowner can know when to switch from (electric) heat pump heating to (gas) boiler operation ?

I know cost of the energy is a big factor, but I am thinking some kind of SWAG/rule-of-thumb say +/- 10-15 degrees.

I think it depends on your "kick-on delay" and how long it take the different systems to reach efficiency.

With a wood burning stove, it takes an hour or tow to get max output, then once you kill the fire it continues to put off heat for 8-10 hours.

Similarly, you have to look at the same rates for the different systems. It is just as much about how much energy is wasted when it is shutting off than when it is turning on.

My .02$ is under 10 degrees or 12 hours, use the 'smaller' option.

 

[chrispyny]

For now !

Plan for the future ! Is it feasible to run piping to those bedrooms either outside or inside the house ? If yes, you may want to buy a larger compressor unit that has 4 or 5 ports, even if you don't install the piping and air handling units for a year or two.

Already thought of that. Since it's a raised ranch, its approx 20ft deep, and 40ft wide. Since i have the left side (east end) of the house taken care of, i plan on installing one more minisplit on the other side of the house (west end) for the three bedrooms. I had my brother in law run a 100 amp subpanel to my garage on the west of the house. So i can easily run electric to the west wall. For the bedrooms, the condensing unit will be imstalled on a wall mount due to a sidewalk on the west side of the house along the garage wall. This condensing unit will have three zones, one for each bedroom. The line sets will run strait up the wall, 2 line sets will terminate at wall mount units in the west bedrooms, and one lineset will pop into the attic and run to a cassette installed in the ceiling of the central/westerly located bedroom wich has no exterior wall to make the install of a wall mount unit possible.
I considered installing one unit for 5 zones but lineset runs would be nuts, and the more zones you add, the more the costs go up, and seer/efficiency ratings go down.
Thats my plan, but the western side of the house will need to wait at least a year. I don't have the money for that right now.

 

[chrispyny]

The other thing is to make sure you are looking at the btuh output, not just the input, that my not be a big difference. With this being said my gut feeling is that you units maybe a little undersized, which wouldn't be a bad thing, it makes everything more efficient, but on the hot days in the summer the the system will struggle, but with that understanding it should be fine.

I value your input on this, (as i do everyone elses of course).

So my 10k btu window shaker is underpowered now. I plan to add almost 2 feet of blown in insulation directly above in the attic,, add ridge venting with a new roof, and bump up to 18k btu output on the upstairs unit from a crappy 10k shaker now, and you think i may be somewhat undersized? Interesting. I can't imagine that but you are the pro so i trust your comment. Can you share why?
Also the downstairs room would be fine with a 5k btu window shaker so i'm pretty sure the 7.5k btu unit downstairs will be more than enough? Also the input vs output btus you refer to i assume are the nominal vs cooling capacity in btus shown on the specs for the cu-4ks24 unit on ecomfort. If so, the cooling cap is 21,400. Shouldn't that be fine for what im planning?

My biggest concern with going heat pump is it does add a considerable amount of money and reduces the btu output of cooling substantially compared to a dedicated cooling only unit. So i'll have to bump up the condenser yet again and spend more money if i go the heat pump route.
See where i'm going?

 

[pseudorealityx]

Going from a heat pump to a cooling only unit will NOT reduce the cooling btu of the equipment. If it does, it's because a manufacturer is lying in their specifications. Typically, the units are sized based off cooling capacity, and actually have slightly more capacity when in cooling mode, because the compressor heat is "free".

<-- another HVAC design engineer.

 

[david86camaro]

I value your input on this, (as i do everyone elses of course).

So my 10k btu window shaker is underpowered now. I plan to add almost 2 feet of blown in insulation directly above in the attic,, add ridge venting with a new roof, and bump up to 18k btu output on the upstairs unit from a crappy 10k shaker now, and you think i may be somewhat undersized? Interesting. I can't imagine that but you are the pro so i trust your comment. Can you share why?
Also the downstairs room would be fine with a 5k btu window shaker so i'm pretty sure the 7.5k btu unit downstairs will be more than enough? Also the input vs output btus you refer to i assume are the nominal vs cooling capacity in btus shown on the specs for the cu-4ks24 unit on ecomfort. If so, the cooling cap is 21,400. Shouldn't that be fine for what im planning?

My biggest concern with going heat pump is it does add a considerable amount of money and reduces the btu output of cooling substantially compared to a dedicated cooling only unit. So i'll have to bump up the condenser yet again and spend more money if i go the heat pump route.
See where i'm going?

With the added insulation you might be okay on sizing. The downstairs unit for sure, hot air rises so most of the load will be upstairs. As for the upstairs unit, I'm sure it will be better than what you have but I'm looking a few years down the road when you can't remember how bad it was with just window shakers. I just want to make sure you get the best info to get what you are expecting.

Correct nominal vs total capacity is what I was referring too, usually 10% lower (20% at altitude).

I'm surprised that the heat pump option derates the cooling. If it causes you to have to upsize besides the extra cost to change to the heat pump, than it maybe not worth the extra cost. But if total cooling is the same the small extra cost for the heat pump would be worth it.


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