Kitchen Drain Waste Heat Recovery

cgw

An architect wants to use waste heat from a commercial kitchen drain to heat fluid for a small sidewalk snow melt system. It sounds like a bad idea but I feel like I have heard of it before.

Even taking the drainage directly from a dishwasher - I would think grease would be a problem.

Any one heard of the application?

bld999

Architect

I have heard of this for residential showers, and if the household takes mostly showers, it can contribute over the long haul. Snowmelt sounds like a recipe for trouble and hi maintenance, with the eventual abandonment of the system and the money it cost to build. [jmho]

Zman

What kind of exchanger

What type of exchanger is he proposing? I wonder if the exchange could happen after an oil separator. The owner definitely needs to be by on board with the maintenance.

bld999

Here's a link .

http://www.gfxtechnology.com/



I think the equipment needs to be in  vertical piping to work correctly.



A bathing shower is a use which makes sense, the pre-heat occurs each time the shower is running. For snowmelt, you would need backup, as the comml. sink use would not necessarily happen when snowmelt was needed. Pumps, valves, sensors, etc all to salvage a little waste heat?

bob eck

Drain waste heat recovery

Is anyone using this and dose it work on a shower? Why must it be in a vertical position?

bld999

Energy-efficient homes

It's popular in energy-efficient homes. It is basically a copper coil [surrounding the waste pipe] that feeds the street water to the hwt. It's sold as a piece and plumbed in. As the fixture runs, heat is recovered from the wastewater. I think the preference for vertical orientation is to maximize the transfer area.



Not a bad idea, depending on the cost. 

Zman

Good for DHW

I think this is a good idea for DHW. As the cold water is pulled into the house it is pre-heated by the waste water leaving the house. There is no need for storage as the 2 events will nearly always happen at the same time.

Snow melt is another issue. There might be enough energy to "idle" the slab some of the time. It takes a tremendous amount of energy to melt snow. How would it be controlled? Maybe they could wait to wash the dishes until it snows? I think this system is best for DHW

Zman

Good for DHW

I think this is a good idea for DHW. As the cold water is pulled into the house it is pre-heated by the waste water leaving the house. There is no need for storage as the 2 events will nearly always happen at the same time.

Snow melt is another issue. There might be enough energy to "idle" the slab some of the time. It takes a tremendous amount of energy to melt snow. How would it be controlled? Maybe they could wait to wash the dishes until it snows? I think this system is best for DHW

Larry Weingarten

I have a GFX...

... in my shower drain and know it does some good.  In this case after taking care of grease, I wonder about timing.  You're trying to use waste heat from dishwashing, presumably to clear snow from a sidewalk for your patrons?  So, they had to walk through snow to come get fed to make dirty dishes to be washed to clear the sidewalk.  Perhaps two systems are needed, one to initially clear the walk and dishwashing to keep it cleared.  Might be easier/cheaper to put the heat back into DHW.  I'm making too many assumptions!



Yours,  Larry

icesailor

$ Recovery:

Another classic example of stepping over a ten dollar ($10.00) bill to pick up a dime ($.10).

Except, in this case, there will be so much money spent for so little return on investment, it becomes a joke.

Only an architect could come up with something like this.

icesailor

$ Recovery:

Another classic example of stepping over a ten dollar ($10.00) bill to pick up a dime ($.10).

Except, in this case, there will be so much money spent for so little return on investment, it becomes a joke.

Only an architect could come up with something like this.

icesailor

$ Recovery:

Another classic example of stepping over a ten dollar ($10.00) bill to pick up a dime ($.10).

Except, in this case, there will be so much money spent for so little return on investment, it becomes a joke.

Only an architect could come up with something like this.

icesailor

$ Recovery:

Another classic example of stepping over a ten dollar ($10.00) bill to pick up a dime ($.10).

Except, in this case, there will be so much money spent for so little return on investment, it becomes a joke.

Only an architect could come up with something like this.

JeffM

vertical

The vertical orientation is needed to make the system transfer the heat properly. In a sloped pipe, all of the drain water flows along the bottom so you only get to transfer heat through the wall to the incoming water in a small portion of the pipe surface area. In a vertical orientation, the drain water flow spreads out to cover all (or most) of the wall - it doesn't just drop right through the middle, water prefers to adhere to a surface. This maximizes the heat exchange area between fluid flows.

cgw

heat recovery?

The way I would do it is a normal snow melt with some sort of heat exchanger on the return to pick up any heat available (which would not be much). I have not looked at a snow melt in a long time so I don't remember what a normal temperature is. The only water in a kitchen that might be warm enough is the dishwasher drain. After the grease trap would probably be too cooled off.

Domestic water would work alot better as it is a lot colder (though I have my doubts).

cgw

heat recovery?

The way I would do it is a normal snow melt with some sort of heat exchanger on the return to pick up any heat available (which would not be much). I have not looked at a snow melt in a long time so I don't remember what a normal temperature is. The only water in a kitchen that might be warm enough is the dishwasher drain. After the grease trap would probably be too cooled off.

Domestic water would work alot better as it is a lot colder (though I have my doubts).

Zman

Sounds Like

It sounds like the architect is trying to justify having a snow melt system be saying it is powered by waste water. This does make him sound very clever, The amount of energy that will ever melt snow is a small fraction of the energy this system could put into the DHW. The DHW system is as simple as it gets, the snowmelt couldn't be more complex. I think the circulators and controls will produce more energy for heat than will the waste water.

bld999

Points Game

As green building scoring systems gain ground, some owners and architects choose building systems with the goal of a big total that they can brag about, get grants for, or in the case of architecture firms, use in marketing materials. I don't mean to suggest that is going on in this case, but there is some natural pressure to do it. Not every generous- pointed system is appropriate for all buildings.

The good spinoff is that people are asked to think about how to save energy. They don't always make the decisions for the right reasons.

Mark Eatherton

Simultaneous demand and load...

are a MUST in order for the GFX to work as designed. I've tested it under three different situations, and have found it to be roughly 50% effective in heat recovery. Not bad considering, but, the load must be occurring at the same time as demand is occurring, or its efficiency drops like a rock.



As for snowmelt, as others have said, it MIGHT throw some normally wasted BTU's at the side walk to keep it in a near idle condition, but it would never have the ability to put out enough heat to completely clear the sidewalk of snow under most conditions. But, if they are looking for points, and they have the proper space to allow a true vertical installation, they would cut the energy consumption of the dishwasher by 50%.



Personally I think that ALL waste recovery potentials should be utilized BEFORE alternative energy systems or even aux. energy systems are deployed. It only makes sense. This includes refrigerant waste heat recovery, which does require some storage, but is definitely worth the cost of participation.



ME

hot_rod

how often does it snow

compared to how often they use DHW? It seems the DHW load would be a better use. If the dishwasher is dumping hot water down the tube, hot DHW must be going in the other end! Perpetual motion?



Refrigeration waste heat should also go into the DHW or heating loads.



I too would give the artichoke credit for thinking outside the box, energy is a terrible thing to waste.



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