Mini Split for a sunroom

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Jasonir129

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Hi all, looking to design a heating a cooling setup for a sunroom addition we're doing in Maryland. It's going to have lots of windows on 3 sides (for what it's worth they're all energy star), a sliding door, and two large skylights (one 4'x4' skylight on each side of the gable). The 4th wall opens to the house. We're planning on doing a good amount of insulation where we can (cathedral ceiling and between windows etc.). Interior dimensions are roughly 12.5'x20'. I did a few pseudo manual J calculations and it looks like a 12k BTU heat pump should be about the sweet spot for heating and cooling.

I'm looking for advice for the slickest setup that would do a good job heating and cooling the space. I don't have a great plan for doing a ductless -- not sure where the best place to mount the inside unit would be and there are too many constraints on the lineset etc with all of the windows (plus the LVL's above the windows).

My current working plan is to get a ducted ceiling cassette and install it in the corner of the room and run hard ducting along the long wall above the windows/next to the LVL. I would do all rigid duct starting with large diameter and step it down in size after each supply. I would then build a bay around the ducting to hide it.

I've attached a picture showing the outside of the addition and another one showing the inside with the proposed high-level idea. I don't know how many supplies to add, duct sizing or any of that -- just starting with the high level first to see what the pros think.

Thanks in advance!
 

Jasonir129

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Fitter30

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Ducted air handler for the mini with spiral duct. Guess this on a cement slab. Electric radiate heat self limiting with a floor sensor thermostat even with a insulated slab it will be cold.
 

Jasonir129

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Ducted air handler for the mini with spiral duct. Guess this on a cement slab. Electric radiate heat self limiting with a floor sensor thermostat even with a insulated slab it will be cold.

Thanks for reply. Generally the direction I was thinking, any particular unit you have in mind or recommend?

Sorry, should’ve mentioned that it’s a raised addition so it’s generally 8-10’ above the ground. Are you recommending radiant heating in the floor?
 

Jasonir129

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There is no better heat than radiate floor. Even with a area rug being elevated floor going to cool with out floor heat.

Sounds good, I'll look into that. Seems like a pretty easy addition before I tile the floor. Guessing I should insulate the space between floor joists from below too?
 

Jasonir129

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Any thoughts on doing a ductless unit in the upper corner where the picture currently shows the ducted unit? Will it effectively heat and cool the room volume including the far end of the room? It's roughly 20' long.
 

Jasonir129

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Any opinions or experience with LG? I'm leaning toward LA120HYV3 which has the heating that works down to pretty low temps. Are they reliable, parts available, easy to work on etc?
 

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A 1 ton is probably oversized for the space. Don't guess, and don't go with pseudo Manual-J, since the natural tendency for humans is to err toward the conservative side. That's fine if you're specifying a gas furnace, but a terrible idea when specifying a modulating heat pump (like a mini-split).

A pretty good easy to use freebie load tool (that is a true Manual-J under the hood) is the HVAC tool developed by the BetterBuiltNW consortium. It was specifically developed by a group of utility companies to help HVAC contractors get their thumbs off the scales and stop oversizing mini-splits. It requires you only to register for a (free) account to use it.
 

Jasonir129

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A 1 ton is probably oversized for the space. Don't guess, and don't go with pseudo Manual-J, since the natural tendency for humans is to err toward the conservative side. That's fine if you're specifying a gas furnace, but a terrible idea when specifying a modulating heat pump (like a mini-split).

A pretty good easy to use freebie load tool (that is a true Manual-J under the hood) is the HVAC tool developed by the BetterBuiltNW consortium. It was specifically developed by a group of utility companies to help HVAC contractors get their thumbs off the scales and stop oversizing mini-splits. It requires you only to register for a (free) account to use it.

Interesting, thanks for the lead. I signed up for the site and am trying to do the calculation but it doesn't seem like the right tool for what I'm dealing with. They require a lot of information on the entire house (some that I don't know) and don't seem to have a direct way to size just for the addition which will only be connected to the house by one wall.

I did several online tools that seemed to size it between 12k and 15k for cooling (and a bit higher for heating). I'm not certain how well I'll get the space sealed up so I'm not trying to totally undersize. I figured the better units like LG, fujitsu, mitsubishi etc can modulate lower to account for potential oversizing or times where load is generally lower. Is this not right?
 

DIYorBust

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Why not go with a ductless wall unit to provide both heating and cooling? You can get a cold climate unit if you think you need that, although you probably don't. The ducted units can be aesthetically nice, since you would just see vents and not a wall unit and one unit can cover more than one room. But in this space, there is no reason to do it. The exposed ductwork would be bulky and visible and a wall unit or ceiling unit can easily do the job since there are no partitions. You didn't show the return location, and you may have difficulty with your plan anyway because you generally don't want 2 feet or so in front of the air handler without a turn.

For a very affordable price you could have a 1 zone wall mounted unit installed, or even DIY it, and it will heat and cool that space nicely. Personally I'd rather it be a little too big than too small here as a sunroom like this could get cold in the winter, but if your sunroom is 65 degrees 3 days a year it won't kill you either.
 

Jasonir129

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Why not go with a ductless wall unit to provide both heating and cooling? You can get a cold climate unit if you think you need that, although you probably don't. The ducted units can be aesthetically nice, since you would just see vents and not a wall unit and one unit can cover more than one room. But in this space, there is no reason to do it. The exposed ductwork would be bulky and visible and a wall unit or ceiling unit can easily do the job since there are no partitions. You didn't show the return location, and you may have difficulty with your plan anyway because you generally don't want 2 feet or so in front of the air handler without a turn.

For a very affordable price you could have a 1 zone wall mounted unit installed, or even DIY it, and it will heat and cool that space nicely. Personally I'd rather it be a little too big than too small here as a sunroom like this could get cold in the winter, but if your sunroom is 65 degrees 3 days a year it won't kill you either.

Thanks for the feedback, I totally agree, I'm convinced to ditch the ducted concept. Now just spec-ing out a ductless.
 

Dana

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Any opinions or experience with LG? I'm leaning toward LA120HYV3 which has the heating that works down to pretty low temps. Are they reliable, parts available, easy to work on etc?

From an efficiency point of view, the load really matters relative to the equipment size. While the 120HYV3 can modulate down to the same levels of the 90HYV3, the efficiency of those units are crap (a COP of only 1.5) when running at their minimum 1023BTU/hr. When running at their AHRI rated heating levels of 13,600 (for the 1-tonner) or 11,000 ( f0r the 3/4 tonner) it's unlikely that even at design temperature the loads are that high, and that at 47F they will be running at a much lower modulation level. At a load of 11K @ 47F the 90HVY3 runs at a slightly higher COP than the 120HVY3 running at 13,600 (which is probably more than twice the heat load @ 47F maybe even 4x), but as the loads drop below 1/4 of the rated capacity it's slipping ever more closely to an efficiency cliff. Going with the smaller one is likely to deliver measurably better efficiency overall, as well as higher comfort.

Notice that at ARHI test conditions for cooling the 90HVY3 still has more than 13,000 BTU/hr of capacity (click on those links in the paragraph above for the COPs & capacities at different modulation levels and temperatures) for those blistering hot days, but DRAMATICALLY higher efficiency than the 120HVY3 at max power when it's 82F outside- a COP of 6.1 for the 90HVY3 vs. only 4.2 for the 120HVY3. Not only will that prove more efficient during the cooling season, by running at a slightly higher modulation level relative to it's maximum it will have a favorable sensible heat ratio, pulling more moisture out of the air than the bigger one.

These are the sort of efficiency & comfort issues that the BetterBuiltNW tools were designed to help contractors avoid inflicting on their clients by using suitably aggressive default U-factors, etc. in the tool, unlike the average Manual-J. As a general rule...

...BIGGER IS THE OPPOSITE OF BETTER!

Right sizing or even slightly undersizing modulating heat pumps tends to deliver better efficiency, as well as better comfort.

There are more efficient LGs than that (with better cold climate capacity too) that don't fall off an efficiency cliff at low modulation, features of the more sophisticated vapor injection cold climate compressors, but they're more expensive too.

Regarding reliability, recent & current model LGs are pretty good and fairly popular- I don't anticipated parts availability to be a problem in areas where many are being installed. Reliability is really a function of the competence & diligence of the installer. If not properly pumped down to a few hundred microns pressure, then charged with nitrogen then repumped to ultra low pressures and held for many minutes (or even an hour) to purge moisture from the system prior to releasing the refrigerant charge, even tiny amounts of residual moisture in the system can shorten system life. This is true for any mini-split, as is installing surge protection to protect the sophisticated control circuits & sensors from degradation due to voltage spikes & surges on the power distribution grid.
 

Dana

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Interesting, thanks for the lead. I signed up for the site and am trying to do the calculation but it doesn't seem like the right tool for what I'm dealing with. They require a lot of information on the entire house (some that I don't know) and don't seem to have a direct way to size just for the addition which will only be connected to the house by one wall.

I did several online tools that seemed to size it between 12k and 15k for cooling (and a bit higher for heating). I'm not certain how well I'll get the space sealed up so I'm not trying to totally undersize. I figured the better units like LG, fujitsu, mitsubishi etc can modulate lower to account for potential oversizing or times where load is generally lower. Is this not right?


I seriously doubt your cooling numbers. I mean SERIOUS doubt here!

If it were a full greenhouse with a single pane glass roof it might hit 15K, but for something with low-E skylights and double pane windows it's going to come in under a ton. And like most mini-splits, even the 3/4 tonner in that series has more than a ton of capacity at 95F outdoors.

And according to my understanding of 'rithmetic 13,000 BTU/hr (=the max capacity of the 90HVY3) is somewhere "...between 12K % 15K..." even in the unlikely event that those loads are accurate (which they absolutely are not.)

In MD your 1% outside design temps are going to be in the ~90F range (lower on the coast) not the ARHI's 95F, so your capacity with the 3/4 tonner will likely be higher than 13K at your actual design temps. The latent load handling (humidity) will take a slight turn for the worse when up-sizing.

Your 99% design temps are going to be in the teens. At +17F outside the 90HVY3 delivers 11,940 BTU/hr, and your heat load is likely to be only 1/2 to 3/4 that high (unless it's all single pane glass in leaky sashes and/or you leave a window open.) That's less than 3000 BTU/hr less than the 14,760 the 120HVY3 puts out. Put into another perspective, 11,94oBTU/250 square feet is nearly 50 BTU/hr per square foot, which is about the load/square feet ratio to expect from an uninsulated shed that leaks tons of air at that temp. Even highly glazed 2x4/R13 type construction with only R19 in the ceiling usually comes in under 25 BTU/hr per square foot if reasonably tight, under 35 BTU/hr per square foot if leaky or single-pane.

It's easy enough to run room by room load numbers with the BetterBuiltNW tools, and get the load for just that sun room. It's worth it to running the room by room load numbers on the whole house, but entering the data as if it were just the one room will still give you the right numbers for ballparking the mini-split.

Note, unlike the xxHVY3 series LGs, Mitsubishi's FH and FS series mini-splits maintain high COPs even at minimum modulation, as do LG's xxHYV1 series (<<<recommended if going with LG.)
 

Jasonir129

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I seriously doubt your cooling numbers. I mean SERIOUS doubt here!

If it were a full greenhouse with a single pane glass roof it might hit 15K, but for something with low-E skylights and double pane windows it's going to come in under a ton. And like most mini-splits, even the 3/4 tonner in that series has more than a ton of capacity at 95F outdoors.

And according to my understanding of 'rithmetic 13,000 BTU/hr (=the max capacity of the 90HVY3) is somewhere "...between 12K % 15K..." even in the unlikely event that those loads are accurate (which they absolutely are not.)

In MD your 1% outside design temps are going to be in the ~90F range (lower on the coast) not the ARHI's 95F, so your capacity with the 3/4 tonner will likely be higher than 13K at your actual design temps. The latent load handling (humidity) will take a slight turn for the worse when up-sizing.

Your 99% design temps are going to be in the teens. At +17F outside the 90HVY3 delivers 11,940 BTU/hr, and your heat load is likely to be only 1/2 to 3/4 that high (unless it's all single pane glass in leaky sashes and/or you leave a window open.) That's less than 3000 BTU/hr less than the 14,760 the 120HVY3 puts out. Put into another perspective, 11,94oBTU/250 square feet is nearly 50 BTU/hr per square foot, which is about the load/square feet ratio to expect from an uninsulated shed that leaks tons of air at that temp. Even highly glazed 2x4/R13 type construction with only R19 in the ceiling usually comes in under 25 BTU/hr per square foot if reasonably tight, under 35 BTU/hr per square foot if leaky or single-pane.

It's easy enough to run room by room load numbers with the BetterBuiltNW tools, and get the load for just that sun room. It's worth it to running the room by room load numbers on the whole house, but entering the data as if it were just the one room will still give you the right numbers for ballparking the mini-split.

Note, unlike the xxHVY3 series LGs, Mitsubishi's FH and FS series mini-splits maintain high COPs even at minimum modulation, as do LG's xxHYV1 series (<<<recommended if going with LG.)

You’re great, I so appreciate you digging in on this with me. Honestly I called e comfort today and they ran their own calculation and told me 15k BTU… which I was suspicious about.

I’ll try the tool again and see if I can get the room numbers. It has a weird requirement where the rooms you add in need to add up to some percentage (I think 80%) of the house square footage. I guess I could just trick it and do a fake room that is the house square footage and so the addition as the second room.

I’m all for getting better equipment if the value is there. I’m confused, are you saying an oversized Mitsubishi will still be efficient to minimum modulation? I’m guessing the comfort and other things will still not be as good? I see what you’re saying, that the btu rating is not the maximum heat transfer rate or there’s a performance curve and that rating is based on some heat transfer rate capability at some specific temperature? I’m with you, I don’t want to over size. My last house had an over sized system and it drove me crazy with the short cycling (fortunately the air was dry, we lived in LA). I knew it was over sized when it was getting installed and I just stayed out of the way as the “professional” insisted that a 1500sqft house equals 4 ton unit (that was his extensive load calculation).

Silly somewhat unrelated question: would it be bad to the equipment if we run the AC with windows open? Wouldn’t it just be in a continuous cycle?
 

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You’re great, I so appreciate you digging in on this with me. Honestly I called e comfort today and they ran their own calculation and told me 15k BTU… which I was suspicious about.

The eComfort tool is downright TERRIBLE, guaranteed to oversize (often by 2x or more!). Note that they call it a "sizing tool" rather than a "load calculation tool" (which it absolutely isn't.)


I’ll try the tool again and see if I can get the room numbers. It has a weird requirement where the rooms you add in need to add up to some percentage (I think 80%) of the house square footage. I guess I could just trick it and do a fake room that is the house square footage and so the addition as the second room.

It's been a few months since I've used the tool, it was spot-on for load numbers on an ~800 square foot house I was consulting on in the Boston 'burbs, coming within 10% of the numbers produced by an engineer using Wrightsoft's professional tools.

No real load tool is as easy to use as the eComfort tool- they need real data on the R-values and construction types since they are shooting for better accuracy. If the BetterBuiltNW tool seems too klunky for you, the freebie online CoolCalc or LoadCalc tools can also get you pretty close. LoadCalc isn't quite as flexible as the BBNW or CoolCalc, in that it won't let you adjust U-factors, and the defaults on air leakage are pretty high. I've found that it often overshoots reality by 25% or more. CoolCalc is more adjustable, but (like LoadCalc) has lots of ways to accidentally have your thumb on the scale, so for newbies unaccustomed to using aggressive inputs (as instructed in Manual-J) it can also oversize by quite a large number. The BBNW tool is good because the defaults are all fairly aggressive, yet it allows you to adjust U-factors when if needed.

If you have to guess what the R-values are, use the highest R that is possible or likely given the age and construction quality. eg: If it's a 2x4 wall, unless you KNOW it's only R11 or R8 econobatts in the cavities assume it's R13. Similarly, set all of the air tightness assumptions for the house or ducts the tightest the tools allow.

Are the windows low-E double panes? If yes, if you don't have the actual manufacturer's specs, assume an U-factor of no greater than U0.35, with SHGC (solar heat gain coefficient) of no greater than 0.30. If you are not sure if they're low-E, look at the reflections of a candle, lighter, or LED flashlight. You'll see 4 reflections, inner & outer surface reflections from both panes. If one of the reflections is a different color than the others, it's a low-E window. Pretty much all double pane skylights built since the mid 1980s are low-E, some with ultra-low SHGC.

I’m all for getting better equipment if the value is there. I’m confused, are you saying an oversized Mitsubishi will still be efficient to minimum modulation? I’m guessing the comfort and other things will still not be as good?

The half-ton and 3/4 ton Mitsubishis don't modulate down as low as the LGs, but they modulate low enough for good comfort. With a minimum output of 1600-1700BTU/hr @ the ARHI test temps (47F and 17F) vs. 1023BTU/hr for the LGs, the difference is roughly the BTU equivalent of one active adult walking around the room, or three humans fast asleep. Both will be running nearly 100% duty cycles under almost any real load, but the Mitsubishi would be using only 1/3-1/2 the power under lighter load conditions, and measurably better during shoulder season average conditions. Without the load numbers and better weather data for your location it's hard to say what that would add up to in annual kwh (or $$$).

I see what you’re saying, that the btu rating is not the maximum heat transfer rate or there’s a performance curve and that rating is based on some heat transfer rate capability at some specific temperature? I’m with you, I don’t want to over size. My last house had an over sized system and it drove me crazy with the short cycling (fortunately the air was dry, we lived in LA). I knew it was over sized when it was getting installed and I just stayed out of the way as the “professional” insisted that a 1500sqft house equals 4 ton unit (that was his extensive load calculation).

The manufacturers bury the "extended temperature capacity tables" in the manuals. The AHRI submittal sheets spec some minimum & maximum capacities at the ARHI test conditions as well as the efficiency at the "rated" or "nominal" capacities, and sometimes the capacities at a couple of other temps. The ARHI test also requires that the inverter frequency be locked at 60 hertz for those tests at those temperatures ( rather than free modulating), so the true efficiency is often slightly better during normal operation than specified. The short-sheet specs on the NEEP pages are from data submitted by the manufacturers under normal operation, but the heating capacity & efficiency hit from defrost cycles is not included, so under some conditions (such as rime-icing fog) the capacity won't be nearly as high as specified, event though it will be pretty close under most conditions. But the NEEP pages show the COP efficiency at multiple modulation levels, rather than just at the AHRI rated modulation levels.

Silly somewhat unrelated question: would it be bad to the equipment if we run the AC with windows open? Wouldn’t it just be in a continuous cycle?

Bad for the equipment, no, but it's bad for efficiency, and under some conditions bad for comfort. Running with windows open in MD would add a significant amount of latent load (unlike in LA or Seattle) in summer, and a lot of the time you would end up cool but sticky/clammy rather than cool & dry. (That's easy to fix- close the windows and run the minisplit in "DRY" or "DEHUMIDIFY" mode for awhile.)

If you need or want ventilation, running a heat recovery ventilator (HRV) or energy recovery ventilator (ERV) would be preferred, since it's a controlled rate not much affected by wind, and most of the heat in the air transfer is retained rather than wasted. (There are ductless single-room HRVs out there that are comparatively easy to install compared to a ducted whole house ERV/HRV. I can point you to a few if you're interested.)

Mini-splits that modulate as low as the LGs or the cold-climate Mitsubishis would have pretty much continuous operation with or without the windows open.
 

Jasonir129

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Sorry, I know this sat a while. Life happens...

I have a friend who is an HVAC pro (he does commercial systems) run load calcs on my addition in his software. He's seeing 17,500BTU/hr cooling and 11,300BTU/hr heating for 72 deg inside with outside temp at 95F and 0F respectively. That's pretty aggressive and probably over designed, I don't necessarily need that. He said when you ease up to 78F in the summer it comes down to ~12kBTU/hr cooling load from 95F. This is based on all of the manufacturer information for the windows, sliding door, and skylights, but he took some rough guesses at insulation (conservative).

He thinks the 1ton is the way to go, but looking at the specs on the MSZ-FS09NA it looks like it could still fit the bill.

Also side question -- any thoughts on the DIY Mr Cool units? Costco sells a 12k BTU unit that seems ok that I could install myself since it has a precharged line set. This could be a consideration if the 12k sizing is the way to go. But if the smaller Mitsubishi would be a big improvement I'm not opposed.

Thanks again for all of your help so far!
 

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If you need or want ventilation, running a heat recovery ventilator (HRV) or energy recovery ventilator (ERV) would be preferred, since it's a controlled rate not much affected by wind, and most of the heat in the air transfer is retained rather than wasted. (There are ductless single-room HRVs out there that are comparatively easy to install compared to a ducted whole house ERV/HRV. I can point you to a few if you're interested.)

Mini-splits that modulate as low as the LGs or the cold-climate Mitsubishis would have pretty much continuous operation with or without the windows open.

Thanks for all of the great information! In addition to my last question I actually am curious about the HRV/ERV. Would this be in addition to the heat pump?
 

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Well think about it. If you oversize the system you will spend a little more money, possibly short cycle it which puts extra wear and tear on it and might leave you with more humid air in summer, and perhaps use up more space somewhere. It may also use a bit more energy, and require a bigger electrical circuit.

If you undersize a little, you will not notice a difference except on days where it is very hot or very cold. The machine will have to run more hours to keep up which could also mean more wear and tear.

If you size the system to perform best when it's zero degrees outside, it's probably larger than it needs to be most of the time. You can also put on a sweater, or use a space heater or open the door and let your space heating system try to pick up the slack. Also if possible, consider improving the insulation and window quality to reduce the needed heating and cooling load.

Another thought, will you have any passive solar gain and did your friend look at that?
 
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