Insight needed on how to use hydronics for residential kitchen makeup air heating

rossn

Hello - On my project I need to come up with a design for using the boiler to temper kitchen makeup air, and could use some ideas on the design.

Seems like a pump, plate exchanger, water-to-air heat exchanger, glycol fluid, and separate controls (24V will be supplied when the makeup air system is on) are likely part of the heating system.

Boiler will be a Vitocrossal 300 CU3A, and will be running mid-temp (130 AWT 20degDelta T at 1F) and low temp (possibly 2 separate low temp zones in the future). Kitchen makeup air (500-1050cfm) will (minimally) need the following BTUs:
0F - 45K BTUs
20F - 40K BTUs
40F - 17.5K BTUs

Initial thought is tying this into the Mid-temp, though I don't know what that will mean when DHW priority kicks in or if there is a way to leverage DHW.

Thanks for your recommendations!

tim smith

Have used First company water to air fan coils for this. Not much to it. Calculate make up air required and btu to bring air from outdoor design up to 70. Pretty easy. Interlock fan coil with kitchen exhaust. Duct stat for discharge air set between 60 and 70 depending on what you want and good to go. They have worked well for me. Re: when dhw kicks in, you probably will be fine to have the dhw and make up air heat work together with heating zones off during priority.
Tim

rossn

Thanks for your insight, Tim. In my case, I would be installing a coil in a duct, as I have an EC fan already that will be used, but the single units sure do look slick. Do you use a plate exchanger and glycol to prevent freezing, in the event the coil stops getting hot water (e.g. DHW priority) and say it's 5F outside? I'll ask my radiant guy the different ways the DHW priority can be setup... in other words, if only certain zone circuits can be enabled when DHW priority kicks in.

tim smith

We don't often get that cold so don't worry so much about freeze up. Yes if you are that cold it might be prudent to use heat x and glycol. Are you sure you don't want to go with electric duct heater, much easier and cheaper to install. Also the # of hrs your hood will run may not pencil out doing the full water to air makeup.

rossn

Good question. Originally, I looked at if we go hydronic or electric, and landed on electric for simplicity and general electrification. However, even though I have 320A service, between planning for future EV charging needs, mini-split, turning the dryer gas to electric, a future apartment above the garage (2nd kitchen and electric dryer + mini split), and hot tub it it doesn't seem I can fit an instantaneous 50A heater load into my capacity comfortably. As it turns out, the duct heater I was about to move forward with modulates, but it is only time based, and not load based. If going the electric route, I then start having to look into looking at energy management solutions, and with the boiler being replaced, seeing if I could do this reasonably with hydronics.

pecmsg

How many CFM's is this exhaust moving?

tim smith

You could also lock out charging load with a contactor when Makeup air heat is needed. This being a very intermittent load would not hurt your charging. Just a thought. Many ways solve this but still will be way cheaper to install than makeup air coil, glycol to water heat x, 2 pumps etc etc and very simple.

tim smith

800 cfm you will probably need appx 60 amps 13 +or- kw to bring up air temp 60 degrees or so at 5 outside.

rossn

Tim - it is possible to lock-out; however the usage patterns and being a load that cycles on and off at 50A does not work quite as well in that situation as, for instance, smaller loads or loads that ramp up. So, an over current protection trip on the main could occur unless I always try to keep other loads totaling < 150A, and at that point, I might the lockout isn't technically needed (assuming there is fluctuation in power consumption). I was sizing a 12kW stelpro heater. Once you go above 12kW with those folks, you start requiring more space/duct distance (and the space requirement is already high). My going-in assumption was that in uber cold weather, we wouldn't run the hood as high, since 95% of the time we're above 15 or 20F and my tempering target was 55F.

@pecmsg - it's a 1200CFM roof blower, but I figure with losses, that maxes out closer to an actual 1050CFM. At the coldest days, I planned on us keeping the CFMs closer to 750 max.

pecmsg

Who sized this
I have commercial kitchens that don’t use that much. 

rossn

I hear you, but when you're over 100k Btus in a range in an island, that's the proper size.

tim smith

There are other options to actual heated make up air. If you bring your makeup air in right near hood, you do not cool down the room, you are just replacing the air being removed. If you look in many commercial kitchens, the makeup air is distributed right at the front edge of the hood through perforated diffuser channel.
This keeps the air in the hot zone and down the front edge of range replenishing the air, leaving the rest of the room not much effected by the replenishment air. Attached is a simple hood dwg, with makeup that many commercial kitchens use. In an island setting you would probably have makeup air along both long sides of hood. Just a thought.
Tim

rossn

Thanks for sharing the idea, Tim! I did check into this originally. What I gathered at that time is that short circuit hoods came about in the 70's at a time when there were additional requirements for ventilation that coincided with the gas crisis and inflated gas prices. Apparently the idea was to get around the legislation and energy loss and high fuel costs, but it generally negated the effectiveness of the hood. I suspect the modern hoods are more effective than the original designs, but what I also learned was that most of the oils that rise up are exiting through the exhaust, not because a blower is sucking them up, but because the heat of the effluent causes it to rise and the particles get captured at the higher velocities on the grates. Introducing the cold are at the lip not only cools that effluent and reduces the likelihood of entrapment, but also reduces the flow of air away from the cooking surface. The various manufacturers of hoods I spoke with all told me to keep my makeup air 10' away, and I couldn't find anything to suggest that a homegrown solution would actually be effective (or at least not detrimental), though I really wanted that to be the case and not deal with all the other issues and energy waste. I couldn't find anything to substantiate a home grown design actually working.

I suspect there are some commercial applications where it works, but that they have both much deeper capture areas, as well as a lot of engineering and testing/validation behind the design. Commercial kitchens are also smart enough to not put a range in the island (our #1 mistake).

Anyhow, that is where I landed originally. At this point, I have physical equipment, framing, etc - so that ship sailed, but do love the idea!

Edit to add: Also, would have been very challenging in my older home remodel to get the air near the hood... almost no attic space.