Factory extraction system heat exchanger general info

[RobWard]

I hope this is the correct place to post this question.
We are a small plastics manufacturer and are looking at building a new factory.
Most of our equipment (ovens etc) has extraction on it.
As we are looking at a new factory we thougt it might be possible to recover some waste heat from the extraction system, probably using it to warm the make up air during cold periods.
The extracted air is pretty clean, but has a very small amount of residual silicone release agent spray in it.
Chemical traces from the processes are to all extents negligible, usually below the levels that can be accurately measured.
I have tried a search here at Eng-Tips, and have Googled pretty unsuccessfully for general information about using heat exchangers on extraction systems. I gather we could possibly use air-air, or air-glycol-air, but I wouldn't know the advantages/disadvantages of either.

I'm trying to find out in general terms what would be involved, whether it's worth doing (environmentally and financially), what sorts of companies could fit such systems, or if it's a non starter.

Could someone perhaps either point me in the right direction regarding what I can measure myself to see whether this would be feasible, or give me some of the proper terminology for Googling with.

Perhaps I should add that we are based in the UK, if that makes any difference.

Many thanks in advance for any advice anyone can offer.

Rob Ward



"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[walkes]

Ashrae HVAC Systems and Equipment Handbook(2000 Ed. chapter 44) has a chart for air to air heat exchangers and the pros and cons of each system type. That may be a good place for you to start.

 

[RobWard]

Thank you Walkes.
I shall go and see how much a copy costs.

Regards
Rob Ward

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[SAK9]

Rob,

Before launching into energy recovery it would be useful to study the benefits.

For eg what is the extraction air qty ?It is considered worthwhile to do energy recovery if your extraction air quantity exceeds at least 1 m3/s

What is the discharge temerature of air from the machine? if it is much higher than room temperature,it may not be useful from a cooling perspective in summer but definitely useful in winter.

The options you have are(in the decreasing order of efficiency):

a thermal energy recovery wheel

a crossflow plate heat exchanger

a runaround coil loop

In case of the first option the extract and supply air come in contact resulting in cross contamination.This doesnot happen in the 2nd and 3rd options

If your machines are scattered all around the factory each spilling out a marginal air qty,there will be a large capital investment to do an energy recovery

 

[HVAC68]

SAK9 is right. You have to do a cost-benefit analysis and the pay-back period to see if it's worth going in for a heat recovery option.

Try "googling" with "Heat Recovery Wheel".

You can get some information from the following website.

http://www.drirotors.com/hrw.htm

If I am right, Greenheck, ABB (or is it Flakt Woods now ?) make heat recovery wheels.

HVAC68

 

[RobWard]

Thanks guys.
At the moment we are just starting to look at this. The factory is still in the planning stages, hopefully on track for construction next year.
We'd have to keep the incoming and exhaust air streams separate, so it appears that would rule out the heat recovery wheel.
I'd like to satisfy myself that it's a practical and worthwile project before calling anyone in and possibly wasting their time.

Currently we exhaust over 2m3/s and that is likely to increase in the new factory. All the exhaust will be through one centrifugal fan, so there will be a scope for fitting a heat exchanger in one place.

The current idea is to bring in make up air from the other side of the factory, so if we decide to recover heat, that might need changing, which alters the plans and we have to discuss it all with the architect etc etc etc.

We're olny a small company, and I don't have anyone above me to offer advice, and we have no experience with this sort of thing. Planning a factory from scratch is proving to be quite some learning experience, and I'm trying to do as much research as I can before calling in other companies and possibly wasting their time, so thank you all for your replies.

I shall google away to try to learn some more.

Thanks again,

Rob


"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[ChrisConley]

From a process point of view a heat pipe or runaround coil system would probably work better than a heat wheel as there would be no cross contamination between the air streams.

If the exhaust stream and make-up stream are a distance a part then a runaround loop is your only option. We have used them sucessfully in many retro-fit and industrial applications.

I've never heard of anyone who has regretted installing heat recovery.

 

[tombmech]

I have regretted it on many occasions. Most of the time, no one ever goes back to check on the unintended consequences. A heat pipe system (along with many others) is a huge maintenance issue. Not to mention there's the whole question of pressure drop on existing systems, and what that does to the fans, other components, and the expected air flow delivery rates. More often than not, fin spacing is optimized for maximum heat transfer, which means you end up with something resembling a filter - and it loads up - easily (i.e. "a dirty coil"). Heat pipe systems represent another point for contaminants in the air stream. There is the heat transfer fluid to take care off (glycol or a refrigerant), and leaks are usually catastrophic - especially if they're in the air stream.

Don't get me started on heat wheels, either.

 

[cme]

There are air/air heat exchangers with separate paths for non-contamination.

 

[RobWard]

Well, it's not looking so straightforward as I had hoped.
I think I shall have to call some people in, to see if they want to quote, and discuss the issues with them.
Thank you all for your replies.

Rob

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams