Heat loads and mini-split.
canadianexpy
| Posted in Mechanicals on
Hi
So had my heat loss calculations done on the new build, and would like some input from people regarding what mini-split they would recommend and placement of the heads, I’m in Zone 6 and the house is single storey with a walk-out basement, total square footage with both floors is 4400.
The following is what they came up with: Main floor Htg load 11889 Btuh, Clg load 12613 Btuh
Walkout Basement Htg load 10792 Btuh, Clg load 2658 Btuh
Total : Heating Load 22681 Btuh
Cooling Load 19582 Btuh
I have attached the floor plan layout with the room to room calculations.
Thanks for any input.
Dave
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So looking at models it seems like Fujitsu and Mitsubishi are the only two to compare. Both have high efficient models and models that can work in down to -15, although not sure I need the Hyperheat/XTLH.
Is there any reason not to go with the Hyperheat or XLTH units, other than I'm sure a price increase?
Can it be overkill, or make the units less efficient.
Looking at Fujitsu 9RLS3YH or Mitsubishi MSZ-FH09NA , I think a pair of these units might work.
Thanks,
Without the 99% outside design temperature there's no way to know if the mini-split has enough capacity. The Manual-J should have both the outdoor and indoor design temperatures specified.
All air source heat pumps fall in capacity with outdoor temperature. With most there is quite a bit of difference in capacity at 0F and -15F outdoor temperatures, either of which could be a zone 6 design temperature.
Are those heating & cooling loads with or without occupants (I'm guessing unoccupied, with the lights off)? Even a sleeping human is good for 230-250 BTU/hr. For conscious semi-active offices 400 BTU/hr per occupant is about right, and any power used by appliances,lights & plug-loads also have to be factored in.
You won't get anywhere near 22681 BTU/hr out of a pair of either of those 3/4 tonners at -15F, but you might get more than 15K.
But if your 99% outside design temp is 0F, not -15F they might be fine.
Dana , it looks like -6F was used as the outdoor temp. (if I'm reading the report right)
OK so I must be not understanding the output of the units , as written on the websites. I thought the Mitsubishi unit at -8 could run at 6700Btuh and max at 12,200Btuh. Which I though would be good enough if I had one on each floor.I guess this is not the way to read these numbers.
Thanks
Here is a copy of what was sent to me so far, with regards to the calculations.
So I’m trying to figure out heating capacity of Fujitsu (and Mitsubishi) units on their website.
Fujitsu site:
9RLS3YH – shows nominal heating at 12,000BTUh,
Min-Max heating - 3,100-22,000
Heating range – 15 -75F
Max Htg % of Model # Capacity at +5 F = 171%
Max Htg % of Model # Capacity at -5F = 156%
Max Htg % of Model # Capacity at -15F= 123%
So at -5 is the output 14,000?? This doesn’t seem to make sense, is the model # capacity 9000? I’m totally confused about this, not sure why I am finding this so difficult to figure out.
I am just trying to get the right size unit for my house.
Thanks
Confused...
I'm not sure why Dana is saying you won't get 22,600 btu/h out of a pair of the Fujitsu units, the manufacturer's heating capacity table @ -5°F has a listed output of 14,000 btu/h. The capacity @ -15°F falls to 11,100 btu/h. A pair would be 22,200 btu/h, which is quite close to 22,600 btu/h. Your main floor cooling load will drive your upstairs unit to be larger though.
As an added note, consider applying for the GreenON rebate for cold climate ductless minisplits, it's a $2500 rebate.
The nominal heating specs are usually AHRI ratings, which don't represent real operating conditions. Dana knows that stuff like the back of his hand from what I've seen and can probably tell you all about how they have to run at a fixed fan speed and can't modulate during the test, etc.
Hopefully Dana will comment back, because as I said I'm confused by the numbers not working?
Anyone else care to chime in on unit placement ...and their experiences?
Still trying to understand capacity's of the units but might have to rely on the salesmen/installer advice.
Any other ways to compare models ? or heating needs?
Thanks
Here is link to a website with a spreadsheet listing most North American cold climate heat pumps.
Great way to compare them but only down to 5°F unfortunately. http://www.neep.org/initiatives/high-efficiency-products/emerging-technologies/ashp/cold-climate-air-source-heat-pump
Might be an easier way for you to read unit capacities and efficiencies
I'll let others with more experience with heat loads continue on the discussion of the capacity of the minisplits.
I'm in zone 6 as well and have done a number of houses with mini-splits as the primary heating & cooling system. I typically place the units in the most open, public spaces and on an exterior wall. You have a pretty closed up plan so it will be very important to make sure you have a ventilation system that is going to keep the air mixing & circulating around the house. I almost always provide supplemental electric heat in the bathrooms as well... Turn it on when you go in for a shower and turn it off when you're done. Your HVAC contractor will be a valuable resource in making sure you have the proper supply & exhaust to move the heat around from your mini-splits. It's also important to remember that a mini-split + HRV (or whatever you use for circulation) is a very different than your typical forced air system. With clients its important to do this education on the front end so that you don't end up with an unhappy user when it's not providing the instant heat & distribution that they might be accustomed to with their old system.
Thanks JMS,
I tried my best to keep the floor plan open, other than bedrooms.but it is what it is.
Outside wall may be tough for finding a good location...
I plan on in-floor electric heat in the bathrooms, on timers.
A whole house ERV will be install, but I realize it will not circulate air like a forced air system.
Yupster.Dave B: The -15F max capacity spec are only at the specified dew point (or wet bulb temperature) in the tables, and it's the instantaneous output, not the net average heat after deducting defrost. It's close (if you don't read the fine print without your rose colored reading glasses on), but it's designing WAY too close to the line for comfort if -15F is your actual outdoor design temp (instead of the later reported -6F, possibly, maybe) and the load calculations happen to be a rare instance of being dead-nuts on the mark for accuracy. Short of looking up the actual weather data and comparing the dew points at -15F dry-bulb, for worst case defrost scenarios deduct 5-10% off of the max capacity in the tables.
The NEEP capacity spreadsheet at -5F are completely relevant at a design temperature of -6F. The fall off in capacity with temperature is smooth, not a cliff.
OK so no rose colored glasses here.
So should the outside design temp be -15F or is the -6F acceptable if its the local weather ? (I'm trying to find the weather info for the area, in-between Toronto and Peterborough) may have to ask designer.
I did give as much detail as possible for the load calculations, but agree it probably is tough to get dead-nuts on( never heard this term before, but I'm going to steal it)
So I assume maybe I should be looking at a pair of 12RLS3YH or the Mitsubishi equivalent ( their site is not very friendly)
I just guess I'm paranoid not to over size, as over the last years of reading the GBA (and your comments Dana)this can cause issues with efficiency.
Thanks 'Dana I appreciate you commenting in on my issue.
Does the NEEP capacity spreadsheet go down to -5F? I can only see down to 5F but I use the OpenOffice version of Excel, which messes with spreadsheets sometimes. If it does that would be even more useful for you Dave!
-6F is the design temp from F280-12 design conditions for Port Hope. So at that design temp the 3/4 tonners should be more than sufficient. But make sure to check cooling capacity as well. Code permits cooling equipment to meet 80% of the load at design temperature, so 15,000 btu/h of cooling @ 75 DB indoors and 87 DB/63 WB outdoors from the ASU15RLS3 would be quite close to meeting your 16,397 main floor load. The heating output is 18,600 @ -5F before adjusting for defrost. It can modulate down to about 14% of it's max capacity.
Yupster, there are some models with information with outdoor dry bulb temps at and below -5F, in my spreadsheet it starts at BB column.
The outdoor unit AOU9RLS3H with this indoor unit ASU9RLS3Y shows dry bulb of -15 and if I'm reading it right Minimum capacity of 1535btu/hr COP of 1.18 and maximum of 11,000 btu/hr COP of 1.44.
The Outdoor unit AOU12RLS3H with an indoor unit ASU12RLS3Y shows dry bulb of -15 and Minimum capacity of 1638btu/hr COP of 1.26 and maximum of 11,500 btu/hr COP of 1.51
not sure which is better for my heating loads, both I think meet cooling demands.
Mitsubishi units seem to have a big spread between the heating and cooling loads ,but again I may be reading this all wrong , as I'm not a building science guru, just a home owner trying to figure things out and gets things right.
Looking at the Manual-J short-sheet, they used a 72F/23C indoor design temperature. I doubt that it's a code requirement, but is that YOUR requirement?
The short-sheet capacity specifications on most mini-splits uses a 70F indoor temperature.
In the US when codes specify the minimum indoor temperature it's usually 68F/20C ( per the IRC.)
The indoor heating relative humidity of 50% is also on the very high side, not that it affects the capacity requirements of the mini-splits very much. An indoor RH of 30% when it's -6F outside is more realistic, unless you're not planning for ANY ventilation. The summary toward the end with the pie charts shows 605 BTU/hr of ventilation losses, but no description of the ventilation anywhere.
The 4F difference between 68F indoors and 72F indoors is already a ~5% thumb on the scale. Unless you really need it to be that warm indoors during the coldest 1% of hours in a year, the heat load would then be more like 0.95 x 22681 BTU/hr = 21,547 BTU/hr for the whole house. The heat load for the higher-load zone of 11,889 BTU/hr then becomes 11,295 BTU/hr @ -6F which would likely still be covered with at least some margin by the 12RLS3H, which has a max capacity of about that much at -15F (according to NEEP data), and 15,000 BTU/hr @ -5F.
The 9RLS3 would deliver 13,500 @ -5F, and will probably just cover it (even net-defrost) at -6F but not with enough margin for extended cold snaps, assuming the Manual-J isn't full of errors.
Since the minimum modulation levels at +47F is the same on both models, there isn't much of an efficiency hit by going with the 1-ton rather than the 3/4 ton, the way there would be if there was a large step in the minimum modulated output numbers.
The FH09NA is only good for 7300 BTU/hr @ -13F and probably not enough for even your 68F indoor load @ -6F. The FH12NA is good for 9,900 BTU/hr @ -13F, and probably makes it at -6F, and the FH15NA's max-14,600 BTU/hr @ -13F would surely make it at -6F.
There doesn't seem to be any internal gains from plug loads or sleeping humans deducted from the heat loads either. Deduct 230 BTU/hr per sleeping human, and 3.412 BTU/watt for any 24/7 plug loads (you can average it for the refrigerator, which normally runs on a duty-cycle).
Thanks for all the input Dana much appreciated, you are one person that I always trust for opinion (also Martin)
I did not call for that indoor temp,, I didn't even notice that. ,Thanks
As for ventilation I was planing on a Venmar ERV X24
Principal venting of 60 cfm and total capacity of 150.
I talk this over I guess with the person that did the calculations
Currently only 2 people and 2 medium size dogs. I need to think on the plug loads.
.
In Ontario, the indoor design temperature required by code is 22°C, or 72°F. The only Canadian I've met who likes it that warm is my mother but code is code. Same goes for internal gains (plug loads and people), you can't include them in a load calc because you can't guarantee they will be present on the coldest days of the year. Although again, not sure why because if they aren't present why does it matter if the house gets a couple degrees cooler?
Since Manual J still has safety factors built in to the heat load calculation, it's okay to size equipment to be close to the actual load. The real load is probably a bit lower. And since the output of two ASU9RLS3 would be ~26,000, 15% oversized @ design temperature, then it seems two 3/4 tonners would be perfectly adequate. But like I said before, you have to upsize your main floor mini-split to cover your cooling loads anyway. If I've got my interpretation of mini-split specs wrong, there would be very few more qualified than Dana to correct me...
So it seems like either a 9LRLS3H downstairs and a 12LRSEH upstairs (for cooling loads) might wok or go with 1 FH12NA on each floor? Not sure which would be more efficient combo.
Like everyone else on this site I'm trying to get what will work the most efficient, and prove the naysayers wrong and boy do I have a lot of them.
That and if I get this wrong and the house is uncomfortable my wife will kill me!!
ASU15RLS3 upstairs actually. You have to combine your sensible and latent cooling loads listed in the report to arrive at the total cooling required for the main floor.
And you would be looking at two MSZ-FH15NA on the Mitsubishi end of things.
Life or death situations like this are how I get my adrenaline high...
Yupster: You can pretty much guarantee that the refrigerator will still be in the same room every day, running pretty much the same duty cycle year-round. Is that REALLY disallowed in Ontario load calculations?
The output of the minisplits will be less at a 72F indoor temp than at 70F (the usual & customary indoor temperature at which the capacities are specified, unless consulting the extended temperature tables.) To compensate for the effects on capacity of that larger indoor to outdoor temperature difference you'd have to look at the capacity at -8F rather than -6F (or -5F).
There would still be enough margin to cover the defrost cycles with a pair of 9RLS3H for the whole house load but it won't be 15%, and might not even be 10% for the whole-house load, and possibly less than 5% for the higher-load zone. You're looking at 13.5K @ -5F / 70F, 11.0 @ -15F / 70F, so at -6F/72F the max capacity will probably be around 12.3K before deducting defrost, to cover a load of 11.9K. (Feeling lucky? Don't care what happens when it drops below -6F?)
There is no need to upsize from an 9RLS3 for cooling. The max capacity of 12KBTU/hr is at an outdoor temp of 95F/80F indoors, a 15F delta-T. The Manual-J calls out 84F/75F, which is only a 9F delta, where it will have at least 5% (and probably closer to 10%) more capacity than the specified max.
But again, there is no real efficiency hit bumping up to the 12RLS3H here. The low end of the modulation range is the same as with the 9RLS3H, and they both start cycling on/off during the shoulder seasons at the same outdoor temperature. With the 12RLS3H you have some actual margin on both the cooling and heating ends, not just a rosy-goggled-fingers-crossed fervent hope that it's really covered. This isn't the sort of gross oversizing that leads to efficiency & comfort problems, rather it is what "right sized" looks like- enough margin that you know it'll work without needing to consult more sophisticated climate & mini-split modeling, and without a ridiculous oversizing factor. At -6F/72F it probably puts out about 13.3K, which makes it only ~12% oversized for the calculated 11.8K load, not a big deal. Even the 15RLS3H would not be more than 20% oversized for that zone, and would work just fine.
If the FH09 could cover either zone I'd be all over it due to it's nice ultra-low minimum modulated output. (But it can't, falling well short of the needed heating capacity.) The FH12 has a roughly 20% higher minimum-modulation than the 12RLS3H, but that's not a make-it-or-break it either. The real issue is whether it can muster the necessary 11.9 KBTU/hr @ -6F/72F (a 78F delta) . I suspect it may still come up short, given that it only delivers 9.9K @ -13F/70F (an 83F delta).
Nope not feeling lucky! (Not with my head in my wife's hands)
I would believe Ontario has goofy codes....
OK so two MSZ-FH15NA(??% oversized)or two 12RLS3H (12% oversized) or two 15RLS3H (20% oversized)
Dana your saying any of these combos won't cause issues, heating,cooling, modulating, efficient. ?
Is the house design make any of these preferred ?I know its a long spread out house.
Thanks Again for your valued input.
Dana, this is the sum of my F280-12 book on internal gains in heat loss calculations. "Not used in Heat Loss Calculations". It's very in-depth. :D
I'm looking at the cooling capacity chart for a 9RLS3H and at design conditions it only pumps out 9,300 btu/h. (See attached picture) Not even close to the 15,000 required for the upstairs minisplit. Do we have different tables?
I'll second Dave here, thanks for your valued input. I don't know where you find the time to answer all the questions you do...
The 15K cooling load is the whole house, latent + sensible, not the upstairs zone. The upstairs cooling load is 12.7K.
The submittal sheet for min/max coolling on the 9RLS3 sez 12K:
https://portal.fujitsugeneral.com/files/catalog/files/9RLS3H6.pdf
In the fine print at the bottom of the first page it specifies:
Cooling: Indoor temperature of 80°F (26.7°C) DB/67°F (19.44°C) WB, and outdoor temperature of 95°F (35°C) DB/75°F (23.9°C) WB.
Note that the capacity table for the 9RLS3 doesn't hit 12K anywhere not even at a chilly subfreezing 15F outdoors, sweltering 90F indoors so perhaps there is some conflicting data or a mis-interpretation I've been making on their intended meaning on the submittal sheet.
In the capacity table it indicates 9310 BTU/hr at 87F/75F, which it ~3.5% higher than the rated 9000 BTU/hr @ 95F/80F (I would have expected a bit more), and 9850 BTU/hr @ 77F/75F (~9.5% more). So at 84F/75F it'll probably be only 5% or so over the rated nominal capacity.
If the capacity tables for the 12RLS3H is similar, using the same +5% interpolation (12K x 1.05 = 12.6K) it looks like it might not quite cover the calculated 12.7K cooling load at 84F/75F but it will be VERY close. Is that is the 75F indoor design temp also an Ontario code requirement? (I'd be surprised if it were.) It won't be insane to install the 15RLS3H upstairs if you really can't stand 78F indoors (or hanging out downstairs when it's not quite keeping up upstairs. If you like to throw mid-summer polka-parties with a half dozen beery dancing Czechs you'll definitely want the 15RLS3H upstairs. Otherwise the 12RLS3H (and a 6 pack of Labatt) should be just enough.
Downstairs a 15RLS3H would be pointless given the lower loads. It looks like the interpolated/guesstimated ~12.3K @ -6F/72F heating capacity of the 9RLS3H would be sufficient for the calculated ~10.8K load (a 14% oversize factor before deducting for defrost.) Even the 9RLS3H would be oversized for the downstairs cooling load. From a cooling efficiency strategy point of view you'll be better off just leaving it completely powered off and letting the upstairs mini-split carry the whole house load until it can't keep up.
I thought my total cooling load was 15270 + Latent cooling 4581 =19582??
So if code allows I might be able to get away with a 12RLS3H (and a 6 pack)upstairs and a 9RLS3H downstairs.
or if I have lots of parties stick with a 15RLS3H upstairs.
Which I think you said won't give me that much of a efficiency hit if i did pick it?
The different summaries on different pages make it confusing, (I was eyeballing the pie chart pages toward the end) but you're right- on page one under "Latent Cooling Equipment Load Sizing" it reads:
"Equipment Total Load (Sen+Lat) 19852 Btuh"
Then on page 3 (for the upper floor) it reads:
"Equipment Total Load (Sen+Lat) 16468 Btuh"
You'll want the 15RLS3H there (if 75F indoors when it's 84F outdoors is considered a must) and a 9RLS3H downstairs. Even the 15RLS3H won't quite keep up with a 16.5K cooling load under high humidity, so there will be days where it breaks over 75F indoors, but not by a lot.
There is minimal efficiency penalties for upsizing within this series, since they all modulate down to the same 3100 BTU/hr minimum. (The minimum modulation varies widely with each size step within the FHxxNA series, as with most vendors' mini-splits.)
Since most days it's never really going to hit 84F or higher the upstairs mini-split can carry the whole cooling load on it's own. Since the cooling load downstairs is low but heavily latent, it''ll be better to leave it off and let the longer duty cycle of the upstairs mini-split keep the house dry, and you won't have energy-burning spin-up cycles multiple times per hour to handle the very low cooling load with the downstairs mini-split.
Thanks Again Dana!!
This seems exciting, to me at-least.
So 15LS3H upstairs and a 9RLS3H downstairs gets me (the house ) it cooling and heating loads. Hopefully my designer and Ontario code agrees.
Now to figure out best placement , I assume over-top a staircase is a bad idea since in the heating mode the vanes point downwards.
Seems like the two of you have got everything figured out. Just thought I'd add for Dana's interest that 75°F is indeed the design temp for cooling in Ontario. What do you expect from Canadians, the colder the better! ;) Helps keep our igloos from melting during our 2 weeks of summer, also known as the season "almost winter".
I am hopeful that the 2 units will work good for my situation, and be efficient, the plan is to get as close to Net-zero as possible. (even if the house is on the large side)
It will be interesting to see what the building permit people think of my plan. They still might not like it.