Interpreting HVAC Plans
I am having difficulties getting answers from the mechanical engineer who designed the mechanical system for the new residential construction in southern ontario.
I would be happy to hear a recommendation for an energy consultant/hvac designer in Ontario who may be open to helping me understand this (“second opinion”) for a fee.
This is what I think is being proposed:
(1) Hydronic infloor heating throughout (this is my request, so some duplication is planned). Uponor quicktrack, 58MBH hot water supply.
(2) Air Conditioning via 1 outdoor, 3 indoor units, central ducts ARNU093M1A4, ARNU073M1A4, ARNU303NJA4
(3) ERV : RERV-C100ECM and RERV-80 via shared ducts with AC.
I would like to better understand why (1) ERV shares ducts with AC and not has own ducts, (2) if I am using hydronic heat only in the winter, is the current AC provision (which also supplies heat) is optimal, and (3) whether I have correctly sized equipment.
For example, if a combi gas boiler is optimal for hydronic and DHW, whether I can instead use two separate electric units for DHW and hydronic floors.
And generally whether the whole thing would actually work well. I am out of my depth on this one and I am mindful of costs (now to install and operating later). The hydronic floor heat is a splurge, I know that.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I'm going to give the same answer I gave in this thread:
https://www.greenbuildingadvisor.com/question/ac-for-radiant-heat
"For warm floors, using an electric boiler and radiant tubing is much more complicated and expensive than just running resistance wires under the floor. You really gain nothing from the radiant tubing.
I would size the heat pump for the cooling load, and get one that does heating as well. Then install as much floor heat as you need to meet your heating load (I'm assuming you're in a heating dominant climate and the heat pump isn't going to meet all of your needs). Pay close attention to how your heat pump derates as the temperature drops when calculating sizing.
Then it's your choice of which heating system to use as the primary and which as the backup. The heat pump is cheaper, the floor heat is nicer. You could even have them on separate thermostats with different time schedules, so the heat pump is primary when electricity is expensive and backup when it's cheap."
In addition: Has your guy run a Manual J? It's impossible to know if the equipment is sized properly without it.
"(2) if I am using hydronic heat only in the winter, is the current AC provision (which also supplies heat) is optimal and (3) whether I have correctly sized equipment."
It's hard to read the attachment unfortunately. You've listed the three indoor units but not the outdoor unit. Together, the indoor units are oversized (I would not expect your cooling load to be close to your heating load), but that might be okay if they're paired with a smaller outdoor unit. The fear with one outdoor connected to many indoor units is that you'll have a zone with a horribly mismatched indoor unit. With the ducted units you have listed, that should be less of a concern.
"For example, if a combi gas boiler is optimal for hydronic and DHW, whether I can instead use two separate electric units for DHW and hydronic floors."
Rarely is a combi optimal for anything - as the name describes, it can do DHW and central heating. It's got to be sized for peak DHW, which often much larger than peak central heating. For example: your heat loss is 58,000btu/hr, so you'd ideally have a boiler with a max slightly above that or a minimum well below that. However, if you expect 1 2 GPM shower to be warm, you'd need about 80kbtu/hr for the shower alone, 160kbtu/hr for two showers. If you were washing clothes with warm/hot water simultaneously, your showers would have varying temps - hot water interrupted by cold water. So sizing larger could fix that (depends) but would then mean you have a combi that's even larger, so sized worse for central heating. But they are cheap and don't take up much space. A boiler can be paired with a tank (called an indirect) or a central heating can be 100% separate from DHW, which is the most common setup. This applies for gas and electric.
I wanted to thank you for your comments on my questions in this thread in the other one - and especially for this comment. I have discussed this "combi" issue with the mechanical engineer and it seems as if splitting the combo boiler could solve multiple issues we were struggling with. We are resizing the equipment and none would have happened if it were not for the kindness of people on GBA to patiently educate me so I could have a more productive conversation.
Thank you.
I have u-values and BTU/hr and CFMs - the trouble is that even with the dictionary it is hard for me to understand.
To answer your question- I have u-value listed in the calculations for all walls at 0.033 BTU-ft2-hr -f*, 0.28 for windows, but then for patio doors and such it is 0.58 (and I have 2 of these). Other doors have u-value of 0.4.
Adding up "sensible" load for cooling I get 39 MBH for cooling. For heating I do not have sensible so I think this is max - for air which is 78 MBH.
For total AC in tons, I get 3.6 tons and the two proposed units for outside were LG for 4 tons and Mitsubishi 3 ton.
I am so confused.
U-values are one of the inputs to the Manual J, BTU/hr is the output. CFMs are derived from Btu/hr.
U-values allow you to calculate heat flow due to conduction. When you're looking at heating, you also need to add something for heat loss due to air infiltration. When you're looking at cooling you add up conduction, infiltration and something for occupant behavior. Then you have to estimate how much solar gain there is, and together they make up sensible. But you also have to look at latent heat -- the energy required to remove humidity from the air. The humidity comes from outside air leaking in, and also from occupant activities like breathing, cooking and bathing. The total cooling load is sensible plus latent.
That's the Manual J process in a nutshell. The output of the Manual J process is a total heating load and total cooling load. You then look at the specification of equipment and pick out something that can meet both the heating load and cooling load. I'm going to guess that in your climate the heating load is far greater than the cooling load, so if you were to pick out a heat pump to do both it would be quite oversized for cooling. But since you want radiant floor heat that's actually an opportunity. What you want to do is size the heat pump for cooling, then size the radiant floor heat for the difference between your heating load and what the heat pump you picked out can put out for heat at the coldest temperature you expect to see (called the "heating design temperature.")
In general, a heat pump can deliver more BTU's for cooling than for heating, because the output of a heat pump is inversely related to the temperature difference, and cooling doesn't experience as great temperature differences as heating.
Let's just toss out some rough numbers to give a flavor. Let's say your cooling sensible is 39K BTU/hr. Solar might be another 10K, latent another 2k, so 51K total cooling load. A ton is 12K BTU/hr, so that's 4.25 tons, they come in half ton increments so you're looking for 4.5 tons of cooling. Let's say the unit you pick out can deliver 80% of it's heating load at your heating design temperature, or 41K BTU/hr. Your heating load is 78K BTU/hr, so you need 37K of heating from the radiant floors.
Rule of thumb is 400 CFM per ton, so you need an air handler and ductwork capable of delivering 1800 CFM for 4.5 tons.
The rule of thumb is a floor can deliver 2 BTU/hr per square foot per degree above room temperature. Above about 85F the floor starts to become uncomfortable, so let's say 85F floor temperature, 72F room temperature, so 13F difference and 26 BTU/hr/sf output. You'd need slightly over 1400 square feet of heated floor to deliver 37K BTU/hr. You also need a heat source that can provide 37K BTU/hr, and if you're going with hydronics you need to do some calculations to figure out the water flow.
But it all starts with the Manual J, if you're not doing the Manual J you're just guessing. But doing a proper Manual J, even with software, is a fair bit of work -- you have to measure every room, every door, every window in the house, and catalogue them all. It really should be done before the job is bid, but installers don't like to do it that way because it's a lot of work that they might not get paid for if their bid isn't accepted. It's pretty much endemic in the industry that installers just guess for sizing. For a complicated system like yours that could be disastrous.
Thank you. I think calculations are done differently in Canada, but that is just an impression. I am including a summary calculation which I believe is similar to what you are describing. Note this is one of the 3 FCU for the house. Does that look like a similar thing?
(My background is closer to engineering than my husband's but I still cannot figure this out).
That looks like the same as in the US. What that report doesn't tell us though is where the loads came from -- whether they did a full Manual J, or just said, "Hmm, 1500 square feet? Let's call it two tons cooling and four tons heating."
This report is only for one zone, I don't know where they get 3 FCU from it. Is 1500 square feet the whole house?
It looks like you want to size the heat pump to be about 2 tons which means the radiant floor is going to provide about 24,000 BTU/hr. That means you'll need about 1000 SF of radiant floor to keep the floor temperatures reasonable. That's actually a lot when you start looking at things like plumbing fixtures and cabinets and staircases and closets.
That's assuming the heat load is based on actual calculations and not just a guess.
ManJ is the same no matter where you go. It is also one of those calcuations where it is easy to skew results and come up with hugly oversized loads.
Based on your initial 58MBH heat loss, say 1.4x oversize factor so 41000BTU/h heat loss. Anything newly build code min in ON should be about 10btu/sqft (rough number but in the ballpark). So if you are building about 4000sqft above grade, the heat loss numbers are in the ballpark. If not, they were not done properly.
It doesn't take much work for you to set your place up here and check (free but they require an e-mail address):
https://betterbuiltnw.com/hvac-sizing-tool
4 tons of cooling in Toronto seems also on the high side unless you have very large unshaded south or west facing windows.
At the current utility costs, running a fuel burner here is more expensive than a heat pump. The warm toes you are hoping to get from the floor heat you'll probably never get in a code min house as the heat loss is too low, the floors will never get warm enough to be felt. With the warm winter we had, I forgot half my floor heat off and didn't even notice.
You are already running ducting for AC so it makes sense to use that for heat as well. The LG units come with hyper heat versions for a bit extra, these will easily deliver the heat you need at the local design temperature.
A bit of spot floor heat is always a nice option for anything tiled, one of the better resistance matts (ie Ditra heat) is much cheaper to install the operating cost is not all that much.
My guess the 7k and 9k heads are for single bedrooms which unless these are ~1000sqft are at least 3x oversized. This means that humidity removal and comfort will suffer as you'll get a lot of cycling. This gets worst if installed on a multi split as the turndown on these is not great. Generally it is always best for efficiency to have each indoor unit on its own outdoor unit.
The report posted in #5 says 30 btu/sf heating, 1500+ SF and 48K BTU/hr.
Thank you very much.
There are 3 FCUs -in additon to the one for 1,500 sq ft, there is also one for 430 square feet, and another for 517 square feet. The first one I posted is for the main floor (living, dining, kitchen, entry) and a family room and office on the lower level (but above ground) - south facing, the other half of that floor is the garage which is not connected to HVAC (north facing). I am including 2 other FCUs.
The other two zones are for second floor only - main bedroom, small office, bathroom, and two additional bedrooms with one bathroom. So a total is 2,500 square feet on mostly 2 floors (with 1000 sq. feet per floor)
The reason heating is oversized is the floor plan. It is an urban lot, so tight. I included the drawing where area in red is the lightwell on the east side (wooded, borders backyards with mature trees) which is all windows. In exchange, there are hardly any windows on the east and none really on the west (wall of the neighboring house is about 5 feet away all alongside that side of the building). The entry (garage) is on the North, street level. The small mechanical room 7X8x8 is next to the garage but the only basement (dug out) area). The outdoor units are going on the west, with bathrooms and kitchen stacked along west wall pretty compactly.
There are fixed and not huge openings on the North, and some operable on the south (Wtih two patio doors).
I think the windows is what creates AC needs; but I suffer from lack of light, so that was my request.
Due to height limits for our zone, there is no attic - rather the sloped ceiling throughout top floor.
I think the summary FCU I posted are based on calculations - there are 15 pages of calculations for each FUC summary I included.
I am happy to post the whole calculation if that helps - I am just trying to respect the mechanical engineer who for all I know have done excellent work. I need to remove the firm name from the PDF I have. It is just asking him questions somehow is not working for me - the gap between his explanation (and patience) and my knowledge is perhaps too vast.
I find any HVAC calc where all 3 floors magically work out to about 700sqft/ton cooling load questionable. At least your main floor should need a lot less cooling.
I would run through the link I posted above and check. Make sure to fill out the overrides properly to match your actual envelope R values and window U values.
Post the results from that and can go from there.
So I entered the numbers off the drawings for floor assembly, wall assembly, and so on and sometimes I had to pick the max available online (because specified is a little higher - e.g. 32, not 30).
I sometimes had no idea what the parameter is (specifically Summer and winter Infiltration ACH so I left them at 0.4 and 0.7 default as in the online calculator).
With all that - and actual u-values for the windows (or as close as I got - manufacturer has 0.29, the online worksheet offers 0.3), I got
Site ID: 13853 Heating: 90,100 BTU/hr
Area: 2,515 ft2 Cooling: 38,500 BTU/hr
Climate: Petersborough Latent: 7,400 BTU/hr
(I picked Peterborough because it had -9 to 85, closer to -13 that the mechanical engineer used)
Does this make sense?
I have a cottage a bit north of Peterborough, it is definitely not Toronto. Using a colder outdoor design temperature is first sign your designer had their finger on the HVAC load scale. Use the design temperature the software picks, it is close enough to the one in the OBC, there is no reason to use a colder temperature. Toronto has seen only a few hours bellow the current OBC design values in the last couple of years.
With a reasonably air tight (say 3ACH @50Pa) 3 story house in cold climate the winter Ach should be around 0.2 and summer Ach around 0.15. A well sealed place, it would be half that value.
The losses seem way too high, post a PDF print of the results page. Once the weather station is picked, you can delete the address and postal code from the site info so it won't show in the results page.
Deleted
Ok, this is the report
(1) Changed away from Peterborough
(2) Used the Winter and Summer ACH as you suggested
(3) Triple checked room sizes/stairs/windows
What do you think?
(The actual construction is 2x6, with R-10 floors on slab, there is only 1 small area that is below ground - about 4 feet deep below grade, 8x10, everything else is slab on grade or second/third floor, all ducts are interior, floor R-31-35-38, exterior walls are R-24+r7.5 CI, Roof R-32)
Is that 1200sqft of glazing correct? In that case, investing in some better windows might be worth it as almost all your heating and cooling loss is through your windows. Due to the local energy rebates, I recently got quoted U0.19 windows for the same price as code min 0.28 ones.
If you do have that much glazing, with slab on grade, floor heat is the way to go for comfort. Air to water heat pump would definitely work but finding install support might be a challenge.
As for cooling, I would still split up the rest of the floors a bit maybe have the top floor on its own outdoor unit and the main and 2nd on a multi split.
Since your losses are pretty high, and you are already looking at LG equipment, one option might be the semi commercial Multi V unit with a hydro kit. This can also pair with standard ducted air handlers, so one unit can supply both your floor heat and cooling.
P.S. Your ventilation losses are also very high which means the model is set for exhaust only, add in the ERV you selected. Won't budge your 5 ton heat loss much but something.
Thank you. I double-checked the windows by going through the window order and calculating square footage for each window from that. It is correct- just a little under 1,200 Sq. ft.
For windows, the software does not permit u-value between 0.2 and 0.3 and less than 0.3 Solar Heat gain and the windows (Weathershield 5 Extreme alum. clad are at 0.26 U value and 0.21 heat gain). The windows are being installed right now, so cannot change anything.
In that case your mechanical designer was not far off. Still not 80K as initially proposed. With the slightly better 0.26 windows and the ERV added to reduce ventilation losses it would put the home around the 5 ton heat loss range.
Your cooling loads are still pretty high as well but less than the 4 tons proposed. There is no reason to install more than 3 tons of cooling capacity.
In case you are worried about cooling capacity, these modulating units generally put out well above their nameplate cooling capacity at our outdoor design temperature. For example the 2 ton LG unit does 3 tons of cooling:
https://ashp.neep.org/#!/product/29592/7/25000///0
thank you. The calculator was a very useful exercise - I could actually see why my figures differ from the designer's (he had an older window schedule, with wrong number of windows and a few other parameters were off).
I asked him to recalculate and resize the equipment - will be back with more questions. If it were not for your help and everyone else who took the time to comment it would not have happened.
Am I missing something? This is new construction with 2x6 walls yet the wall type is set for 2x4 with poor insulation?
That is a default chosen by the software - it comes with the following description:"Note: Default insulation level below is meant to provide a starting point for the house you are evaluating. You are able to override any specific items on later pages to override these default values. Please take care to override where neccessary."
There does not seem to be anyway to modify the default, but I modified R-values and U-values when possible.
Having done more research - and in addition to the questions above - what are your views on
(1) ERV sharing ducts with HVAC. That reduces the number of openings in the walls - which is a plus IMO (aesthetically) but I have read articles here and elsewhere that it is preferable to keep them separate.
(2) Single exterior unit vs 3 exterior units for cooling. There are 3 floors, all above grade except for 8x10 mechanical room which is 4 feet below grade. Half of the lower floor is garage (not on HVAC). Current zoning is 1 zone for the ground floor (half floor, 450 sq feet or so), plus 1,000 sq feet main floor. Then two separate zones for south side and north side for the top floor (about 450 sq ft and 550 sq ft each, for a total of 1,000 sq. ft). Logically it seems simpler to control zones with several units. Aesthetically three exterior units begin to look like kraken - especially if water heat pump is added, (see below) making it four.
(3) Is there a calculator for electric load like this great HVAC calculator? I am trying to see if 200AMP service be sufficient for all-electric house (cannot easily get more than 200amp service).
(4) For all electric house the local code - SB-12 - requires an additional inch of CI which the current wall assembly design does not accommodate. But there is an exception to that requirement if "if the primary space heating of the building is supplied by (a) a wood burning appliance, (b) an earth energy system, or (c) an air or water source heat pump that does not use electric resistance as a back-up heat source" - would using an air to water heat pump for hydronic heat and the air to air heat pump for cooling/backup heating meet this requirement? If the domestic hot water purely electric resistance? Or am I trying to be too clever?
(5) What do people in all electric houses do when the power goes out? I am planning to put solar panels at some point (was thinking of a simple design without batteries, just to provide the "standard load" and not send anything to the grid. But that presumably cannot be a backup system. I am trying to avoid connecting to Natural gas at this point, so a natural gas backup generator does not appeal for that reason (among others). I have kids, power outages are tougher with the kids.
"What do people in all electric houses do when the power goes out?"
It's not that much worse than a house with gas, pretty much all gas appliances need electricity to run these days.
If you want to have emergency heat so you can shelter in place, I would recommend a portable propane heater. One that's 30K BTU/hr will run 14 hours on a barbecue tank. That would keep you from freezing.
We are putting in a clean-burning woodstove in lieu of the fireplace, so can use that for heat., but I was thinking more fridge/lights. Here we get ice storms in the winter, but also summer storms when the power goes out for a while. But I did not think to look at barbecue tanks - seems there are similar propane-tank based generators. That might work.
You can get a gas-powered generator to run a fridge and a few lights with extension cords starting around $300. From there they sky's the limit.
Our power goes out regularly here in Maine, for anywhere from a few minutes to a few days, but usually it's for a few hours. We have a portable gas-powered generator and extension cords to power the essentials (coffee maker, fridge, freezer and wifi router) and plans to add a manual transfer switch so we can power the whole house.
That's too hands-on for most of my clients so we often install a whole-house backup generator, usually propane-fired.
Clients always ask if battery technology is sufficient for backup power. It can be but it's still an expensive option and only gives you a day or two of power at most.
I have a full suite of Makita battery-powered hand tools and have thought about getting their battery-powered coffee maker, so I don't have to fire up the generator just for that task. They have battery-powered lighting as well.
We have a small urban lot, so not much room for a large whole-house backup generator anywhere. I was thinking of may be eventually having enough solar and solar backup batteries, but that is not currently in the budget. But the small propane "essentials only" electricity seems feasible with a propane barbecue-size tank.
I have not researched yet, but I imagine there is a way to do electrical layout so that my built-in fridge for example can be connected to the backup power easily? I am thinking of "circuits a" and circuits b" where A has the fridge and WiFi and may be an outlet and B has everything else and I can connect "a" to the backup power?
Reply to #27: choosing specific circuits to provide with backup power is a long-standing practice, but some electricians won't do it because if someone later adds more circuits the generator would be undersized. Maybe the story is different with a propane-tank generator; I don't have experience with those.
To use a water heater for hydronic heat it has to be rated for space heating. So far as I know there aren't any residential electric water heaters that are rated. This is one of the reasons I've been trying to guide you away from electric hydronic and toward just resistance heat for the floor, providing electrically heated hot water gets complicated.
If resistive heat is out, an air-to-water heat pump isn't a terrible choice. It's what I have in my own house. It's kind of experimental, but I'm kind of a mad scientist. The one I use is the Chiltrix. It has resistance backup heat, but it's an option, not a requirement, basically it allows you to get away with a smaller pump and use the backup heat on those 99th percentile days.
It's going to be the same story with your air-to-air heat pumps, you can disable the resistance backup heat but you'll have to size up a bit.
Thank you - you were helpful here and in the other thread. I truly appreciate you taking the time. We are now considering a version of what you described here.