Manual vs electronic zoning
I contacted an energy rate consultant to help my builder increasing the energy efficiency of my new house and reach DOE net zero ready performance. The energy rater advised to use a centralized ducted heat pump (located in a mechanical room in the basement), ERV using the HVAC ducts and manual zoning (basically opening and closing the air grill) to control the temperature in the house. Manual zoning is definitely cheaper than electronic zoning (automatic dampers that allow to reach a different target temperature at each floor) but I am a bit confused. Shouldn’t a HVAC system be commissioned to verify all specified flows at the air grill? If I open/close the air grill for manual zoning what’s the point of commissioning. By the way I also received a quote from Zehnder: $15k without commissioning and installation. A bit too much, especially without commissioning which I believed was one of the main reasons to go with their systems.
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If the occupied parts of the house will generally be on the same level, the windows are evenly distributed, the R values of wall and ceiling are consistent and you plan to keep all the room at the same fixed temp 24-7 then manual zoning should work well for you.
If you expect the basement bedroom and the second-floor bedroom with sloped ceiling over the garage to be the same temp while the thermostat schedule is set to change 4 times a day from the south facing greenhouse on the main floor, manual zoning may not be the best option for you and your home.
Commissioned is a vague term in residential HVAC work. They will do their paperwork while the unit runs for 10 minutes or so and wave a hand over most of the registers and call it good. Generally the contractor prepared manual Js are a joke and measuring air flows and adjusting air flows to match a bogus numbers would be a waste of time.
If you have an independent manual J and you want the system air flow adjusted to meet it be sure that work is listed in the bid.
Walta
Thanks Walta. So if I want rather uniform temperature between basement, first and second floor electronic zoning with 3 separate dampers and thermostat is a must. I am also planning to leave the basement unfinished for few years. Any idea how the efficiency of the variable fluid heat pump would be affected by electric zoning? When the basement is not heated/cooled the hvac system would be oversized so wondering if it can lead to eccessive cycling. Maybe a ducted minisplit per floor would be a more efficient solution than a single heat pump but probably more expensive?
My two examples are both extreme.
If you are asking me would I zone a basement? I would not and did not spend my money zoning my basement. Knowing the basement would contain a shop, exercise room and a spare bedroom. My basement walkout basement is always cooler than upstairs and I kind of like it that way.
You did not tell us much about your new home but before I chouse zoning I would consider 2 separate systems seems to me the redundancy of separate systems is worth some extra cost.
Seems to me most basements even walk outs are very small cooling loads and adding an electric heater or two would cost very little to install and not a lot to operate depending on the set point.
My opinion EVR/HVR are silly unless your home is in the frozen north zone 6 or 7.
Are we talking about upgrades for a production builders home.
Walta
Thanks Walta. I agree that a basement can be cooler and does not require a perfect temperature control.
This is a custom home and I am trying to get a DOE net zero compliant house. The builder has no experience on net zero so I am hiring an energy consultant. By the way the energy consultant advised an ERV with simplified ducting that here on GBA is continuously criticized for its limitation. Also with the HVAC system he is advising (single zone with manual air grill adjustments) no idea of what the air change and ventilation in each room is. Now you are telling me to avoid ERV.... this is so confusing! I guess it really depends what are we prioritizing, cost, air quality, energy efficiency, convenience, etc.
For a new build I would go with a ducted mini split per floor. With a central return and shorter supply runs, it might be cost neutral with a central system. This will give you zoning without complicated controls.
I would install a Panasonic ERV on each floor with the bathrooms ducted to the exhaust and ducting the supply to the mini split return.
Hello Kyle,
I agree with you about the simplicity of 3 separate ducted mini splits vs a zoned centralized system. A centralized zones system is intrinsically less efficient and hard to commission properly and if not properly designed it would be a distaster. Minisplits I believe are more 'plug and play'. Not sure about cost though. 3 separate ducted minisplit and 3 separate external units might be way more expensive, unless we use only one external unit but then efficiency might go down quickly.
Questions:
-What you mean for "central return"? (1) all the rooms served by each minisplit are connected to the same central return for all 3 floors or (2) we have a 'central return' per floor?
- I like the idea of the hybrid ERV system but wouldn't be better to install the ERV supply on supply side of the ducted minisplit as suggested in post#12 https://www.greenbuildingadvisor.com/article/ducting-hrvs-and-ervs
Thanks!
A ducted mini split the size needed for a single floor of a new build costs around $2k? That puts you at $4k to $6k in equipment cost depending on whether you do the basement. That is easily in the price range of a larger fully modulating air handler with heat pump. You should have less duct work as well.
Central return per unit located in a hallway or living space.
With ducted mini splits the fan is always running if it’s on, regardless of whether it is at setpoint. Ducting to the return allows your outside air to be conditioned by the mini split and doesn’t force your ERV fan to work against the static pressure of the mini split fan.
In my opinion EVRs don’t make sense without a large temperature differential from outdoors to indoors without it there is little to no energy to recover. Ventilate if you must with less than 20° difference nothing is being recovered.
The ventilation recommendations make no sense to me. All to often it turns out there are very few people hours per square foot. Often 2500 sqf per person and it turns out they are away 10 – 16 hours a day.
Most of the houses don’t get a blower door test making it a pretty safe bet they if tested the air changes per hour will be closer to 3 than to 0.6.
Yes, you need an ERV if there are 6 people living in a thousand sqf in Canada in a home tested at 0.6 ACH50 but short of that I think we need to be reasonable about where and when they are needed. Some will be along to disagree to say no house should be without an ERV.
Kyle last time I looked the Panasonic’s were not rated for use in the bathroom.
Walta
Most homes even ones even ones at 3ACH need mechanical ventilation. A leaky house doesn't guarantee the leaks happen where people are so there is a good chances that indoor air quality is pretty bad in a closed room. There are many houses I've have walked into over the years without mechanical ventilation where you can smell the stuffy air as soon as you walk in the door, I'm sure a lot of them were above 3ACH. A house with a properly setup up ERV/HRV always smells fresh.
How that ventilation is best handled depends a lot on climate. I'm in colder climate so energy recovery makes sense. Energy recovery that costs $15k does not. It definitely is a challenge to come up with a cost effective solution that also works, it doesn't have to be an HRV/ERV, in some climates that could be a venting dehumidifier. The one that does not work is relying on bathroom exhaust fans. Even in hot climate, an ERV might make some sense. We were near our summer design conditions yesterday (~92F), based on the dew point of the fresh air supplied to house, the ERV saves me about 3200 BTU of latent cooling. Not a lot but definitely something.
The Panasonic install manual specifically mentions ducting to bathrooms, maybe mounting the unit there is not the best idea but running bath stale air pickups is not a problem.
I'm with Kyle on the setup. Slim ducted unit for each floor, if you put the main floor one into the basement ceiling, it is easy to add a couple of registers to condition the basement.
I would suggest a single larger ERV. Less maintenance and fewer holes in the building. The hybrid ducted setup does tend to be good compromise, make sure to select an auto-balance type ERV so it won't be effected by flow rate changes in your air handler.
Hello Akos, all very good points!
When you say " put the main floor one into the basement ceiling, it is easy to add a couple of registers to condition the basement" are you suggesting to use one ducted minisplit to condition both basement and first floor? This would definitely help decrease the cost.
Regarding the ERV: I did not know that auto-balancing ERV even existed! Would auto-balance allow to get the flows specified by design independently of the air handler status? Any specific model/brand you would suggest? The Zehnder quote I received showed a request flow of 192 CFM at medium speed and suggested a QE 600 (max flow 350 cfm).
Thanks!
I was able to find only one manufacturer of auto-balancing ERV https://www.broan-nutone.com/en-us/ai-series
How come there is not article about auto-balancing ERV on GBA yet? Looking forward to it :)
In a new build with a well sealed envelope and basement insulated to code min, the heating load there is very small and the cooling load is almost all latent. In most cases a register or two and return is all you need, so if the main supply trunk for the 1st floor is running along the basement ceiling it is as easy as punching a hole into it and putting in a ceiling register. You can also easily add on a couple of supply lines if the basement is ever finished.
If you are in radon land, it is also good to add an ERV stale air pickup near the ground in the basement.
For auto balance unit you can also look at Panasonic Intellibalance and Zehnder Q series. The Zehnder ERV units are not that expensive, most of the cost is the accessories. You can save a fair bit by using standard ducting with it.
Great suggestions, thanks again. So I have a mechanical room in the basement so can I install a ducted minisplit on the ceiling of the basement in the mechanical and feed into first floor and basement or ducts would get too long? Also I suppose that each minisplit would have a separate external unit?
You are right about the Zehnder system: of the total 15K cost, 11K is for accessories and 4K for the ERV unit. And thanks also for the radon hint, that something that Zehnder did not do even though I am in a radon area.
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Hi Walta what about comfort? ERV should also minimize temperature/humidity gradients between delivered fresh air and the room. I read here on GBA an article showing that even with 3ACH50 CO2 levels went above 1000ppm in bedrooms.
"Hi Walta what about comfort? ERV should also minimize temperature/humidity gradients between delivered fresh air and the room. I read here on GBA an article showing that even with 3ACH50 CO2 levels went above 1000ppm in bedrooms."
I have yet to see the news reports about people suffocating in their air tight houses. Its not going to happen if a room gets stuffy and it could a few times a year I think you are equipped to recognize that you are uncomfortable and intelligent enough to conclude cracking open a window will improve your comfort and if you open the window too far for too long, I think you will close the window before you become uncomfortable in the other extreme.
The way I see it 1000 ppm is a scarry sounding number that they now have equipment to measure not a death sentence your body is equipped with much better sensors but it does not print reports.
Walta
Cococchio,
This is a reply to #15 as we ran out of nesting.
Long duct runs are never an issue provided the ducting is designed properly. Medium static slim ducted units can do up to 0.6" of pressure which is not far off from a standard furnace air handler. Even feeding two stories with a mid static unit is not a problem.
A bit of design work up front can make the install much simpler and cleaner. I would have an HVAC engineer design the ducting for you and than work with your architect to integrate into the building. Things like floor trusses with duct chase and roof plenum trusses can make the install much simpler and cleaner. Returns can lot of times be hidden inside thicker interior walls, behind built in cabinets or back of closets.
As Kyle has pointed out, the equipment you need is very cheap. Two zones even with brand name hardware is under $6k. The problem is that if you take this design to most standard HVAC installers they will charge you magical pricing that is 5x to 6x BOM cost. Besides doing it properly, this is why you want the design done by some else and have a general contractor install all the ducting, pour the concrete pad for the outdoor unit and run wiring. The HVAC person should only install the equipment and connect it up.
You always want each zone on its own outdoor unit. BOM cost is about the same as a multi split and you get much better modulation range, higher efficiency and a bit of redundancy.
All excellent points. I would also add if you can find a small one or two man HVAC company or know someone in the industry you may have a bit more luck with someone looking to do something new.
Akos thank you so much! I have an engineer running manual J,D,S but he is the one that suggested me a single heat pumpunit. Hopefully, he is familiar with ducted minisplits but I am not very hopeful. A $30K to $36K for the minisplit systems is scary! I guess I really need to ask for multiple bids once I get the final design and maybe look for small HVAC company as Kyle suggested. Problem is that for a DOE Net Zero Ready certification of the house I should use a Energy Star certified HVAC installer... not sure I would pay that much extra just to get a certification though!
There is nothing wrong with a single air handler. That is how most houses get built and can be made to work. It does require a larger air handler and more ducting. To get it to work well you need an oversized return near the ceiling on the 2nd floor to reduce stratification but chances are you'll also need dampers (manual or thermostat) to adjust the 2nd floor temperature.
If you look at the equipment costs, the larger high static air is about the same cost as the two smaller slim ducted units. Except for the install costs, there isn't a huge cost save by going with a single unit. HVAC trades would be much more comfortable with a single high static multi position unit, so it would be the easier path if you can't find good trades.
When I looked at the all the certification programs, I did not see how jumping thru the required hoops added any real value to the home. Yes, you get a piece of paper to hang on the wall but I have no plan to sell the home in my lifetime and even if I did would the appraiser increase his opinion of the houses value? I think not one dime. Will a house sell for more with a note saying it the passed the now antiquated “2022 net zero ready” requirements from 20 years ago?
Each of the certificate programs seemed to come with some baggage I disagreed with. The one I found most offensive is the limit on the size of the home to no more than X number of square feet per resident. Is that part of your net zero program?
Consider the “pretty good house program” but you will not get a plaque
Walta
No I do not believe there is a limit on size if you go with the performance (via modeling) instead than prescriptive approach. I am using modeling to optimize the envelope of the building but probably I won't go ahead with certification UNLESS some good incentive would be proposed by the county. I believe there are counties that offer full tax credit for 5 years for DOE net zero ready buildings. Pretty good house program is a very reasonable approach but I would love to see some good product coming from it like a software or tools in general rather than only generic and often obvious statements. In other words more science and less blah blah blah. Hopefully the new book will prove me wrong...