Ducting and ERV
I am completing the design of a new house in zone 4a. I received a design and quote from Zehnder for a energy recovery ventilation system. Total cost of the quote is 15K.The quote includes comfotube, shipping and all accessories but it does not include commissioning and installation. The target airflow from the ERV (Q600) is 192 CFM and on boost mode would provide the max flow of 353 CFM at 0.8” water.
My builder and energy rater are advising against this system due to the high cost and complexity of duct system. Energy rater is advising an ERV in simplified mode connected to HVAC ducts and funs in the bathrooms. I pushed for a hybrid system with exhaust-only ducts from the bathrooms and kitchen and he is not against that. Problem is that with a simplified or hybrid system I would not have any idea of how the fresh air is distributed. Is that a real problem? The ECM motor of the handler would run continuously and mix the air so that might not be a problem.
If I go with fan in the bathrooms a boost mode might not be required so I could use smaller ERV units but otherwise I could not find other ERV with 353 CFM for residential application.
Installation of Zehnder in my area is another problem. Zehnder referred me to a private that does installations but he does not have a company so my builder will likely refuse to work with him.
So in conclusion, I would love to have fully separate ERV ducts (it is a new house) to have a control in room by room airflow but:
– cost of the Zehnder system might not be justifiable
– installing a Zehnder seems to be problematic at least in my area
– Zehnder is not providing commissioning in my area
So is there any other company that can provide a similar system? To be honest I could not find any! I would love to to hear your suggestions, thanks!
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Replies
It's super rare for total cost of an installed HVAC system to be less than twice the cost of equipment and materials, so assume you're looking at $30K all-in.
Sounds great if you have lots of money to burn, but seems excessive to me.
I have a Broan ERV. Fresh air is dumped into hallway ~6 ft from the return serving all of my bedrooms for heating/cooling. I have a Fujitsu mid-static unit which is basically always running, albeit sometimes at low speeds. So far, so good. I intend to do some CO2 monitoring to quantitatively see how well it's performing, but the total installed cost was less than $2K, so I feel like I could re-do it a couple times over before hitting Zehnder $numbers.
Do the Broan units also allow recirculation in addition to fresh air? I really like that feature of the units that offer it. I think it would be helpful to keep balanced temperatures in rooms if you only use a mini split or two in the house, even with the low CFM.
The Zehnder cost is wild. I was quoted around $6700 for a Minotair unit, closer to $9k once you include a hydronic inline heater/cooler and everything to install it except the ducts.
Thanks for your replies! The Broan ERV250 ECM goes up to 241 CFM at 0.4" w or 259 CFM at 0.2" w. Those flow value are not enough to double the target flow of 170 CFM in boost mode. The Zehnder Q600 has about 350 at 0.8" w so it has the ability to pull trough long duct lines. Not sure if the Broan can do the same. Also the Zehnder has a counter flow exchanger vs a cross flow exchanger (les efficient) Broan. A hybrid ERV system (exhaust from baths, kitchen and maybe laundry) with the Q600 the system would cost about $7500 + installation and commissioning. Basically, half the price of the fully ducted system but still likely double compared to a Broan system. Installation of Zehnder might still be a problem if I do not find an installer in the area.
4A is not that cold to be worth while spending big $$$ on energy recovery. $9k or $15k is silly money for equipment only. 170CFM for base flow also seems very high unless you are looking to run a yoga studio at home. Select a reasonable base flow rate and pick a unit that can a do a bit more than base on boost. I'm not sure where this 2x number is from but that is not a must.
I would go for one of the autobalance units (smaller Zahnder Q series, Broan AI or Panasonic Intellibalance). The Zhander price is not too bad if you only look at the cost of the actual ERV and don't use their fancy ducting, registers and silencers.
A hybrid ducted setup is minimal cost increase compared to a simple ducted setup, saves you a couple of exhaust fans and wall caps. If you look at the overall BOM cost, the hybrid ducted setup is actually a bit cheaper and about the same labor.
Where I would spend extra HVAC money on is getting a modulating heat pump instead of a simple one or two stage AC. These are significantly quieter, more efficient and since the blower is running 24/7 it will give good mixing of the supplied fresh air. Even fancy hyper heat equipment is only $1k to $2k more than a furnace+single stage AC.
We had a Broan AI series spec’d for our house and the designer designed it exactly as Irish said, ducted completely separate from the HVAC and with the supplies next to the returns for the ducted mini-splits so the supply air can be both further conditioned and distributed to the other rooms. I read the installation manual and it seems really easy to install by any competent HVAC installer or even a very competent DIY’er because it’s self-balancing and the instructions state to, “design and install ducts in accordance with ACCA’s Manual D.” If you’re already having ducts installed by an HVAC contractor, this would just be more of the same. It seems that you could install several of these for the price of the Zednher if you really want/need a lot of ventilation.
The instructions also state, “The way your heat/energy-recovery ventilator is installed can make a significant difference to the electrical energy you use. To minimize the electricity use of the heat/energy-recovery ventilator, a stand-alone fully ducted installation is recommended. If you choose a simplified installation that operates your furnace air handler for room-to-room ventilation, an electrically efficient furnace that has an electronically commutated (EC) variable speed blower motor will minimize your electrical energy consumption and operating cost.” If you are concerned about energy efficiency, it seems that keeping it separate from your HVAC system is the way to go. Also, you want to be careful about over-ventilating because you lose energy twice. First on the extra electricity to run a larger motor and second on the extra air that needs be conditioned because no ERV can transfer 100% of the heat from one air stream to the other. There has been much written about the actual amount of ventilation needed and I admit that I am no expert and I had our systems professionally designed.
Superman, to answer your question, the Broan AI series that was spec’d for our house can operate in recirculation mode with most installation configurations and the installation manual shows diagrams of the different configurations and which can operate in recirculation mode. I got all the docs for our model from the Broan website and I will attach the spec sheet below. I imagine that some of the other economically priced ERV’s from other manufacturers can do the same but I only looked at the one specific to our application so I don’t have info on any others.