reclaiming heat from dryer exhaust

[lsmennenga]

We are trying to think of ways to reclaim the exhausted heat from our bank of dryers to inable us to heat the laundry mat itself. Has anyone tried this and are we just dreaming or can it be feasible if done properly. What are the pitfalls? Has anyone tried it? Thanks sue

[Duane]

Sue,

I am working on this and it will be installed in my new mat in the next few months.

Results will be posted.

Duane.

[Xiong]

We are trying to think of ways to reclaim the exhausted heat from our bank of dryers to inable us to heat the laundry mat itself. Has anyone tried this and are we just dreaming or can it be feasible if done properly. What are the pitfalls? Has anyone tried it? Thanks sue

still remember long ago i post something like this here and many thought i'm nuts, now i know i'm not the only strange one.

i think it's a smart thing to do, why the heck just let all those hot air go out the door?

[Adamski]

Guys,

Once upon a time ...

... There was a company that developed a cube shaped heat exchanger that fit onto a dryer exhaust duct. The claim was that it would pick up heat from the hot air being exhausted out of the dryer and heat a separate flow of air going into the customer space for space heating purposes. Well, the things never caught on probably due to required maintenance and technical issues.

One must consider that dryer exhaust air is humid and linty (is linty a word?). So anything that you put into the exhaust airflow is bound to clog up fairly quickly. Even a little lint buildup on that heat exchanger would reduce the efficiency and effectiveness of the dryer. That's why even today dryer exhaust heat is disposed of outside without trying to reclaim it.

[mjwalsh]

We are trying to think of ways to reclaim the exhausted heat from our bank of dryers to inable us to heat the laundry mat itself. Has anyone tried this and are we just dreaming or can it be feasible if done properly. What are the pitfalls? Has anyone tried it? Thanks sue

Sue,

For 2 winter seasons now we have utilized reclaimed dryer heat to help heat our dog wash building addition. For us it has made sense. It consists of a sealed inner aluminum rectangular ductwork (inner chamber) that has open access on both sides for fairly easy lint removal (approximately 1-2 hours) once a year. We plan on getting an attachment of some kind to make the lint removal more thorough for the rectangular ductwork. The size of the opening exceeds the manufacturer's specification to avoid potential problems. At our kingkoin.com website there is glimpse of the exterior of the exhaust ductwork.

There is an outside larger insulated aluminum ductwork (outer chamber) where an effective fan circulates the air out into registers that we open up during the winter time to help heat our still extremely new self service dog wash. Proper controls to consider the heat available & the heat need is needed. In our case we were using a PLC anyway.

We know it works & we have through the PLC the logging capability of the various pertinent temperature changes to gather data like in a lab setting but have not done the more scientific approach data gathering at this point ---- other than knowing that it definitely is harvesting heat from eight of our dryer exhausts with out any drawbacks or safety issues.

I am thinking some of you on the forum have a common horizontal duct for some of your dryers without problems if sized properly.

The properly sized & insulated outer chamber & the properly sized fan mounted & registers are the added costs but your building layout or potential layout would have to also be a good fit. Being in a cold enough area where heating is often required or helpful is also an obvious factor. We were thinking long term & we needed to do something with our existing dryer vents to do the addition to our building to accommodate our brand new DIY dog wash service.

Any suggestions on the lint removal attachment from anyone ---- on mentioned above --- to make the lint removal extra thorough on our inner rectangular ductwork? The rectangular duct is about 19 feet long with the cross section being 17" square. Access is from both sides. Right now we just use a rag secured on a long bamboo pole on a day with a very strong (from the North) wind blowing naturally every fall of the year.

Mike Walsh king koin of bismarck north dakota

[subati]

Sue,

For 2 winter seasons now we have utilized reclaimed dryer heat to help heat our dog wash building addition. For us it has made sense. It consists of a sealed inner aluminum rectangular ductwork (inner chamber) that has open access on both sides for fairly easy lint removal (approximately 1-2 hours) once a year. We plan on getting an attachment of some kind to make the lint removal more thorough for the rectangular ductwork. The size of the opening exceeds the manufacturer's specification to avoid potential problems. At our kingkoin.com website there is glimpse of the exterior of the exhaust ductwork.

There is an outside larger insulated aluminum ductwork (outer chamber) where an effective fan circulates the air out into registers that we open up during the winter time to help heat our still extremely new self service dog wash. Proper controls to consider the heat available & the heat need is needed. In our case we were using a PLC anyway.

We know it works & we have through the PLC the logging capability of the various pertinent temperature changes to gather data like in a lab setting but have not done the more scientific approach data gathering at this point ---- other than knowing that it definitely is harvesting heat from eight of our dryer exhausts with out any drawbacks or safety issues.

I am thinking some of you on the forum have a common horizontal duct for some of your dryers without problems if sized properly.

The properly sized & insulated outer chamber & the properly sized fan mounted & registers are the added costs but your building layout or potential layout would have to also be a good fit. Being in a cold enough area where heating is often required or helpful is also an obvious factor. We were thinking long term & we needed to do something with our existing dryer vents to do the addition to our building to accommodate our brand new DIY dog wash service.

Any suggestions on the lint removal attachment from anyone ---- on mentioned above --- to make the lint removal extra thorough on our inner rectangular ductwork? The rectangular duct is about 19 feet long with the cross section being 17" square. Access is from both sides. Right now we just use a rag secured on a long bamboo pole on a day with a very strong (from the North) wind blowing naturally every fall of the year.

Mike Walsh king koin of bismarck north dakota

Hi Mike,

Nice description. Few questions purely out of scientific curiosity...
1. What is the temperature difference you observe between the start and the end?
2. Since you are essentially cooling the already damp / humid air, have you observed any condensation occur? If your inlet air was very close to saturation point and the temp drops below the saturation due to the cooling, you would notice condensation.
3. Do you see any pressure drop or air backflow?
4. Since this is gas/gas heat exchange, it is normally very inefficient. How does the cost of installation + maintenance compare to the cost savings on the heat?

Su Ti

[mjwalsh]

Sue - 1. What is the temperature difference you observe between the start and the end?

Mike response - We do not have a temperature sensor on the output -- We do know that the inner chamber is usually 180 degrees. The aluminum surface transmits to the outer chamber & the fan routes the otherwise wasted heat to the register openings.

Sue - 2. Since you are essentially cooling the already damp / humid air, have you observed any condensation occur? If your inlet air was very close to saturation point and the temp drops below the saturation due to the cooling, you would notice condensation.

Mike response - Moisture makes the process more conductive to the surface like we need ---- if anything it should help --- especially if there is a slight film of lint on the surface etc.

Sue - 3. Do you see any pressure drop or air backflow?

Mike response - No, because the opening is to both sides of the horizontal duct & the sizing more than meets the manufacturer requirement for air flow.

Sue - 4. Since this is gas/gas heat exchange, it is normally very inefficient. How does the cost of installation + maintenance compare to the cost savings on the heat?

Mike response - It is a very conductive surface heating an insulated air space which the fan blows the 100% clean & 100% safe air into our recent dog washing 150 sq ft addition. It would be nice to have a better handle on the precise cost benefit ratio. It would be a good project for our higher level educational system to partner with --- so they could possibly earn their keep???

Mike response - Maintenance cost should be a non issue because the PLC controls other things anyway & the permanently lubricated blower fan should last for a very long time. We do have a small furnance filter on the intake of the blower fan. Sometimes the laundry gets warmer than needed in the winter just from the equipment running & this blower fan actually recycles some of that heat also routed through that air space between the inner & the insulated outer chamber. Precise synchronized controls are important.

Mike Walsh King Koin of Bismarck

[BN82]

Make certain that you maintain manufacturer airflow specs, or you'll have massive headaches.