Pizza Oven Heat Recovery System

Paul Cooke

Will be working on a new pizza place that plans on using the waste heat from the hood to run through the slab. And also DHW.

Is anyone here familiar with any off the shelf equipment for this application?

Thanks

Mark Eatherton1

Here's an article

on that same idea..

http://www.sustainableportland.org/stp_best_cs_hot_lips_02.pdf

I'm still Googling...

ME

Mark Eatherton1

Here's a possible company..

to make one for you.

http://www.specialized-mechanical.com/products/iht_furnace_heaters.html

The only thing I can offer is that you're going to be dealing with a SUBSTANTIAL v.o.c. load in the air stream side. Maintenance and cleaning will need to be taken itno the scheme of things, or it will become clogged, unplugged and removed.

I can't tell you how many really good ideas that would save TONS of valuable resources I have seen over the years fall victim to the side of neglect, then eventually be taken out.

Waste heat recovery IMHO, holds one of the greatest conservation potentials that we can do immediately...

Still googling around.

ME

Paul Cooke

Pizza Heat

Mark

Thanks. I'm about an hour and a half from the pizza place you found in your google search. The owner of the place I will be working on has been in touch with the Portland pizza place.

They are using their waste heat to provide their hot water needs. Not sure if they have one or two ovens. Was planning on calling them Monday. We'll have two ovens and plan on heating the slab and making hot water for the
kitchen.

My understanding is that there will be a substantial no. of btu's to be harnessed here. What I wonder is whether or not what we will be doing would be considered "making" a boiler. 25 years ago we used to put heat exchangers in wood stoves. Don't think I would do that kind of thing today because of liability.

Mark Eatherton1

While they're at it...

have them consider the possibility of doing refrigerant waste heat recovery for their DHW preheat. Now THAT makes cents:-)

Been there, done that, saw it pay for itself in 7 years.

ME

Mark Eatherton1

It depends...

on the attitude of the State Boiler inspector. I think it would be a good idea to try and run it by the State authority. Nothing worse than getting it installed, paid for and then being told to take it out and give the money back.

What concerned me was the supposed btu/day availability. I'm hoping it was a misprint, because 120,000/day btu's won't go very far towards ANY load, be it space or DHW...

Good luck to you Paul. I'd love to see more of this type of system happen.

ME

Paul Cooke

Hot Pizza

Mark

I talked to the owner of the Portland pizza place this A.M. and he is using the waste heat in an open loop for hot water to his dishwasher etc. He's pumping to a 50 gal storage tank which is in series with a 100 gal electric water heater. The breaker to the 100 gal heater has been left off since the installation last year and they have more hot water than they need. Apparently the system jumps to 120* in about a half hour and then climbs to 180*. They have been dumping excess hot water on some days. Too bad. They should set up a utility company and sell it to their next door neighbors.

They are using a stainless coil w/ fins enclosed in a 10" duct for the heat exchanger.

Unknown

This was attempted here in RI

a while back. Problem was the Department of Regulation would not approve it as there was no standard established for testing the system.

I would suggest you get a design engineer from a restaurant equipment company to develop the plans. Then you will have to hire a third party testing agency to test and perhaps set a standard. The cost for that is usually about $30,000 to $50,000.

The restaurant I referred to above had to tear out the entire system.

I just dug out some more info on the heat reclaiming device that was attempted. I knew there was something that the gas company had found that was an additional problem. It was a very high Carbon Monoxide level in the two 8" flues which had the coils installed for reclaiming the heat. One of them was operating with 1500 ppm the other was over 2000 ppm.

That has to be addressed along with design requirements.

Mark Eatherton1

Obviously...

the article had a misquote in it. Doesn't suprise me though... Non technical writers in a technical world.

There used to be some stainless steel heat scrubbers that were applied to the exhaust of boilers back in the mid to late 80's. Not even sure if they're still in business or not. If they pulled too much heat out of the exhaust plume, their extraction pump would shut down to avoid super cooling of the flue gas and condensation production. Maybe someone with a better memory than mine can remember their name.

Here's a picture of a heat reclaimer from Parker Boiler company that might work.

ME

Bill N.

I'm all for heat recovery, but 7 years

Here is one of the classic problems with any plan, idea or scheme to conserve energy (recovering waste heat is a great example). To purchase, maintain and operate some piece of equipment that saves energy but has a payback of seven years is not on the radar of most businesses.

Think of it this way, if you own a business, do you think you'll still be in the exact same business seven years from now? For a lot of busineeses (and potential customers for me) the answer is no.

I've seen the only people who can afford such a long payback are people who won't be changing their business in the next ten years or more. For instance, schools or certain parts of government. For a new restaraunt to spend the extra money now in a business venture that may close before seven years passes makes no sense(think about how many restaraunts close or remodel or change ownership in less time than that).

I'm in the energy saving business, I would love if these facts weren't true, but we have to be mindful of the simple fact of commercial life when we offer these things to our customers.

A good friend of mine has a saying about heat recovery. The best, highest temperature and highest quantity of heat for recovery is always on the wrong side of the building or has terrible gasses in it that go on fire when condensed. Keep this in mind.

Bill N.

Mark Eatherton1

Most people that do conservation....

aren't doing it for the "R.O.I.". Most are doing it because it's the "Right Thing" to do, environmentally speaking.

If it were all based on ROI's solar would never stand a chance.

That said, business' generally get to expense the equipment anyway, so the cash on cash ROI is somewhat moot. Bottom line, it saves energy.

ME

Paul Cooke

I agree

Good point, Mark. The folks who take the risk and make the investment with alternative energy sources often spend more money than they ever get back. They do it because it's the right thing to do.

By the way, today I had a good conversation with the outfit that installed the heat exchanger on the pizza oven. There's an adjustable damper on the device and he has it set to keep from creating any condensate. He's measured the oven's improved efficiency at about 16%. Sounds good to me.

With gas prices continuing to rise, payback here could be less than a couple of years.

Bill N.

Your statements are true, but I haven't met

seen a lot of businesses where they consider cash an expense and "free". I don't own a business (the Man oppresses me every day) but I have friends and peers who do and to them every dollar counts. One business owning friend didn't want to upgrade the flourescent lighting in his leaseed space, even though he pays the electric bill. Why? He might move when the lease is up and the payback (or ROI, or PV, or a million different economic ways of looking at money) was longer. Why improve the lighting for the next guy at his expense.

That being said, you will find customers in the market who DO want what is energy saving, what is good for the environment. These customers are the rare ones that I come across. Not to say other people don't invest in their businesses, but when they spend money, it has to make money for them right away.

You will find people who have paid for and use fuel cells, solar heating and photovoltaics. I have seen most of these people have this expiremental equipment (I say expiremental because if you look at the companies that made solar equipment in the 1970's and look at who sells it now, there aren't a lot of common names) because they have want it.

I love the idea of conserving energy, but being in the energy business exposes me to a lot of customers who won't spend a single dollar that won't be back in their pocket next year. They would rather spend that cash on something like advertising or better ingredients or new paint.

That all being said, we are people who can help change this behavior in the market place, but we have to do it carefully. Nothing is for free, in fact, when I meet vendors or manufacturers of products who tout their one year paybacks, or free energy, or whatever, I become discouraged; my potential customers are seeing the same ads I see and perhaps viewing me as selling something for nothing. The economizer coil in the pizza oven vent will save energy. It will also require extra cash during building construction, it will require regular maintenance, it will one day leak or break or go on fire or something. It will require some additional control components and require the troubleshooting person responding to a "too hot" complaint one day to understand how the free heat is staged with the fuel fired heat. The owner has to know these things before he invests. The other problem is the owner will never know with certainty how much energy he is saving, without spending even more money for metering and datalogging.

Keep selling efficiency!

Paul Cooke

Good points

Bill

Your description of the life cycle of this heat reclaimer seems pretty accurate. Yes, it will take $ to do it, and, depending on how good the design is will determine the installation cost, maintenance and longevity of the system. This owner has other quality restaurants here already. He's young and should be around to enjoy the R.O.I.

There will be 2 ovens in this place and the plan is to take care of the hot water load and also warm the slab during
the heating season. We're just taking the btu's out of the stack and temporarily storing them in some water for dishwashing and the slab. I suppose if you look at the big picture, the contribution to global warming remains the same.

Someone will visit this place next winter and sit down by the window that faces the street. It will be 34* outside and raining. His pizza will be hot, his feet will be warm, he won't know about the coil in the stack, but, he will be comfortable.

flange

nice idea, tried to do it on a much larger scale a few years ago. everyone liked it except for the equipment manufacturer. something about intended use etc. im all for conservation if possible, but check with the manufacturer. it may save some headache later.

Unknown

Paul you had better

do some real combustion testing on those units. My experience with them (I ran a restuarant service business in the past)has not been good. They tend to have very high levels of carbon monoxide in the flue.

I worked very closely with several restaurant equipment companies in the past and every type of reclaiming device they tried was not able to be within safe ANSI standards for carbon monoxide. Most of them tested up in the 1500 ppm to 2000 ppm range. They also had very high maintenance as they kept sooting up.

Maybe someone has designed a better system as I have been out of touch with these for several years.

jim f

why not build the oven with bricks and mortar and run pex tubing in the design and pick up btu's that way. assuming its a brick oven?
jim f.

Paul Cooke

Tim, Jim and everyone

Pizza Oven Update: Went and looked at 4 pizza ovens (stacked 2 high, side by side) similar to what will be in the place under construction. They both have a rectangular exhaust vent at the rear on top. A large hood sits above the ovens with a 12" round duct that runs up through the roof. There is an exhaust fan that comes on when the ovens are in use. There were some serious hot fumes making their way up that vent pipe. Well over 400* according to my digital thermometer.

We probably could place a heat exchanger coil in the duct and make sure that we don't cool it off enough to cause condensation. But, here's what I think I might do: The large, flat tops of these ovens were around 150*. I can build the equivalent of an unglazed flat plate solar collector and secure it to the oven top. No need to interrupt the flue gases. What do you think?

Unknown

Sonds great Paul and .....

less likely to cause any combustion problems. We have a Fish and Chip restaurant near me and the owner has a duct system rigged up to blow the warm air from the kitchen area out into the supply duct on his heating system. This in turn partially heats the dining area and bar area.

He rigged this up about five years ago with his brother who is in the sheet metal business. They had a degree day /CFH study done about two years ago. I just talked to them this morning about it as I am curious about what you are looking to do. The savings they had calculated on their heating bill was about 20% savings. These figures may be off a little bit as they also have two commercial gas water heaters. There is however in that dining room always a cooking smell in the winter, who knows maybe that helps sell more seafood.

Bill N.

I start to think about the purpose of what you are doing

I don't want to seem like the doubting Bill here, but if you install a heat exchanger on the top of the oven, aren't you now spending more gas in the oven to keep the oven at temperature (likely whatever quanity of heat radiates into the air will be less than what you take out of the oven when you get a HX in)? Would you save more money by adding insulation to the top of the oven? The pizza place by me keeps the boxes with the cooked pies in them warm for the will call orders. Will the HX interfere with that?

I know somebody else on this post suggested adding PEX tubing inside the construction of the oven, but I think that is the same thing, you are taking btu's out of the oven that would not normally have left it.

Just something else to think about.

Bill N.

Paul Cooke

Good points

I understand what you're saying here. If these ovens were properly designed they wouldn't be losing so much heat off the top. Seems like they should come from the factory with more effective insulation on top. Unfortunately most restaurants buy used equipment and most of these old ovens tend to overheat the space they are in.

My hope is that we don't cause these ovens to work harder by placing a HX on top. I do plan to insulate above the exchanger.

And, you're right about keeping the cooked pizzas warm by placing them on top of the ovens. That's what they do around here. I suppose we'll have to install gas-fired warming oven to do that now. ;-)

Greg Swob

Not a pizza oven, but

I recall reading an article some years back - during the tax credit days of yore for renewable energy upgrades. As I recall, a firm in California had devised a means to recover waste heat from a crematory (oven?) to help heat a funeral home. Some felt this was a little morbid using waste heat from such an originally intended source, but on a practical view: waste not, want not. Greg

AKO

Great topic!

The product Mark attached looks like a possibility worth consideration as long as the cost isn't too much. Another common approach, if you haven't already discussed it, might be a run around coil (used in lab applications among others). It uses off-the-shelf products: a multi-row coil with pumped distribution to what ever system you want to use it for, maybe an indirect tank in this case. There are a lot of options with this type of system.

AKO

Great topic!

The product Mark attached looks like a possibility worth consideration as long as the cost isn't too much.

Another common approach, if you haven't already discussed it, might be the use of a run around coil (used in lab applications among others). It uses off-the-shelf products: a multi-row coil with pumped distribution to what ever system you want to use it for, maybe an indirect tank in this case. There are a lot of options with this type of system.

Mark Eatherton1

Adds new meaning to the term...

dust to dust, ashes to ashes, don't it?

Did I say that? I didn't just say that didI??

Just kidding!!

I don't think there's much caloric value to a cadaver. I'm sure ASHRAE knows though...

ME

Aidan

Pizza Oven Heat Recovery

I think I’d try a run-around coil type system, with finned coils in the exhaust duct. You could use the water to heat the make-up supply air and/or DHW, possibly via a plate heat exchanger. I don’t think the alternatives would be practical (cross-flow plate heat exchanger or thermal wheel).

The heat recovery coils in ventilation systems are typically 4 or 6 rows deep and add a considerable resistance to the extract fan duty. An inverter drive on the fan could allow the fan speed to be varied to maintain a constant negative pressure. Also, if there were only one oven on, you wouldn’t be extracting the air, and heat, required by 4 ovens from the restaurant. This alone should save some money. However, a good controls contractor could charge more than the mechanical plant costs.

The mass flow rate of the fluid x it’s specific heat capacity should be the same value for both air and water streams. I suppose this is the same for imperial units. The water should flow counter-flow to the air direction (the air entering from the oven meets water leaving from the coil first).

You not only condense the water vapour, but also any grease. You’d need to be able to get the coils out to clean them, possibly by steam cleaning (do the cooking fumes go up this duct, or is it just combustion products?). Possibly also have 2 or 3, 2-row coils in series so that they’re not too heavy to be lifted out for cleaning. The grease is a fire hazard, but the restaurant owner should be getting the extract ducts cleaned regularly. You may also need filters upstream of the coils, to catch any solids or paper towels. I’d put propylene glycol in the water, if it’s to be used to warm fresh air and connect to the coils with flexible hoses with 2 ball valves, to minimise the loss of coolant.

If you get a run-around coil system running, there’s very little to go wrong with them and they can go on quietly saving money for years without needing attention. There must be someone making this equipment already, are we re-inventing the wheel?

There was a crematorium with heat recovery in the UK, I believe. It was thought that they kept a stack of bodies and threw them into the fire as required.

Unknown

There isn't.

But from the Half million BTUH gas burner, there sure is.

Who's going to clean it?

Art Pittaway

SlantFin or other

copper fin tube boiler manufacturers make great heat exchangers, I wonder if a boiler assembly could be used in the exhaust duct. Done right it could be removed for cleaning as an assembly. I've been looking at the pottery kilns at our college, right now the heat is lost. The kilns are electric but the problem is glaze can be toxic and it all stinks when firing is done. These kilns run in the 1500+ degree range because they are melting glass and even with the insulation there is a lot of heat lost. Any thoughts?

Art

Unknown

Art, Slant/Fin boilers are all Cast Iron.

Noel

Greg Swob

speaking of cleaning

I looked into some sites for crematory refractory firms and found their latest concern seems to be silicone implants which melt. On firm suggested you should cremate these clients at the end of the day so you don't have to clean out the byproduct between 'customers'. This and other residues cause serious cleaning problems. Guess we all have our maintenance concerns. Greg

Art Pittaway

OOPs,....Duh, sorry Noel.!

I mean Tele-Laars, Ray-Pack, RBI(?), Lochinvar, etc.

Art

Bill N.

Keep us posted

I am very interested in what you accomplish. It sounds to me like your owner is savvy enough to understand what's happeneing, and you can obviously put words together to form a sentence, so he should know what you know.

Let us know what you eventually do there. Maybe make a warming box on top of the oven, without a door. Make the box from sheetmetal, then insualte the outside of the tin with 2" of fiberglass, then enclose the insulation in another layer of tin. I would suggest a door, but that door will get ripped off the first busy Friday night. This way you could let them keep the warming spot, but save some money in the process. The only problem would be keeping the air from convecting out of the box, along with all the heat you are trying to save.

Maybe try a door made of clear plexiglass, so the workers can read the numbers on the side of the will call boxes, then flip the door up (spring loaded hinges). Of course, in doing this, are you over cooking the pizza for the customers who wait too long to come pick it up? Nothing is easy.

Bill

Douglas Hicks

Gaylord Industries, Inc in Tualatin, OR 800.547.9696 has produced heat exchange type I exhaust hoods. I think there system was to heat the make-up air for the exhaust hoods.

Whatevr the outcome, please keep us informed.

Douglas Hicks
General Fire Equipment Co of Eastern Oregon, Inc

Graeme

Bumping an old thread

Hey guys,



Sorry to bump and old thread. I am an engineering student at montana state university, and a part time employee at a pizza shop here in bozeman montana. I am trying to design a system to pull excess heat from our pizza oven in order to heat water for dishwashing. It sounds like this guy in PDX has exactly what I am looking to build. Does anyone have contact information, or at least a name of the pizza shop?



Thanks!



-g