[Bldg-sim] exhaust air liquid heat recovery loop

chris.malcolm.yates at gmail.com chris.malcolm.yates at gmail.com
Wed Jan 20 03:50:11 PST 2021

Nicholas, I think this is one big tangent! But your point illustrates that heating is as much a heating process as it is a cooling process. The traditional laws of thermodynamics (I did have to check them) don't describe this in an easy to understand way... So I'll just call it "Newton's 3rd law, but for thermodynamics".


Regarding potentially long refrigerant runs. We see refrigerant dual purposed as the heat transfer medium in heat-pump AHU's such as the Flakt Woods model I linked to earlier. However, I'd like to consider "dual purposing" the CHW loop for heat recovery in winter. In Europe we are much more familiar with piping chilled water around buildings to terminal units. So, distributing heat, cold and recovery via 4 pipes to remote AHUs probably won't be so much of an issue.


There is also the potential to push low grade recovered heat back to recharge ground-source boreholes. By doing this, a smaller borehole array may be sufficient and heat pumps may operate at a more consistently high COP. Recharging boreholes shouldn’t take any compressor power, just pumping.


Based on some other conversations, the low gas costs and high capex of these systems are a barrier. 






From: Nicholas Caton <Nicholas.Caton at se.com> 
Sent: 20 January 2021 07:29
To: chris.malcolm.yates at gmail.com; 'David Eldridge' <DEldridge at grummanbutkus.com>; 'Jim Dirkes' <jvdirkes2 at protonmail.com>; bldg-sim at onebuilding.org
Subject: RE: [Bldg-sim] exhaust air liquid heat recovery loop


I don’t think I can add much to the original prompt/discussion, however just chiming in to add a voice of consensus from the gallery, if only for your collective sanity.  I have seen runaround loops implemented a few times in the simplest sense (closed water loops with glycol/antifreeze capturing exhaust stream heat specifically to precondition incoming OA).  Effective energy savings potential during extreme heating/cooling seasons, however the associated pump circulation energy can eat up savings potential during nice weather in between (seasons/temperature based controls advised).  


These systems at sufficient scaling and in climates with extreme winter/summer preconditioning needs (in my specific experience:  large laboratory / healthcare facilities with high volumes of 24/7 exhaust/makeup in the Midwest US) can definitely pencil favorably for implementation in retrofit scenarios.  I have never personally encountered refrigeration loops applied as a solution to this specific sort of building exhaust heat recovery challenge, but it sounds like a great idea on paper.  Whether this really pencils well however will depend in part on relative proximity of the OA inlet and exhaust airstreams.  Considering the large scale applications in my portfolio of experience, I’d observe the points of exchange (OA inlet / Exhaust stacks) were typically far removed, spatially (basement/ground level AHU’s pulling in air vs rooflines/attics for exhaust) – so very long compressor/refrigerant runs might prove to be a critical feasibility/cost-limiting factor in application, relative to a simpler closed hydronic loop (circulating water over long distances can be easier).  I guess I’m a biased fan of runarounds – but don’t discount the potential to really optimize savings of existing systems with proper controls/sequencing.  These are often not operated/installed as intended/designed (just circulating 24/7), so even if something is already in place you might have some low hanging fruit to grab there 😉.


**Tangent Alert**


I’m in the middle of a project to implement a souped-up version of exhaust heat recovery, but not for buildings.  Application is a series of large existing steam boiler plants (Combustion stack economizers)!  This will entail installing heat recovery coils (and bypassing infrastructure) onto existing large boiler plant exhaust gas stacks.  We can then capture the heat in two stages:  First stage pulls boiler exhaust gas (~400F to atmosphere) down ~100F with a loop to carry that heat into the deaerator process of the boilers.  Second stage (condensing) economizer cools the combustion gasses further (~130F to atmosphere), applying that energy to pre-heat makeup/feedwater coming into the boilers.  


Thought it might be interesting for some to cross-connect the potential for heat recovery systems in a broader sense.  My experiences with deconstructing and optimizing typical building mechanical systems was definitely a bridge for figuring out how to approach and do the same for hydronic plants – this is one of those sorts of mental bridges that helped me to get where I am.


**Flailing effort to get back on point Alert**


I wasn’t the best student through my chemistry courses decades ago, but I have a sneaky feeling that sticking a typical refrigerant filled line/coil in a boiler exhaust gas stream with hopes of recovering heat might just pose a small risk of violent explosions and total catastrophe… I’ll leave that one for the rocket scientists among us to chew on =).




Nick Caton, P.E. (US), BEMP

ニック ケートン, P.E. (US), BEMP

Senior Energy Engineer
Energy Manager, Yokota Airbase 

ESS - Energy & Sustainability Services


+81 . 070 . 3366 . 3317

+1   . 785 .  410  . 3317

 <mailto:nicholas.caton at se.com> nicholas.caton at se.com

ESS - エナジー持続可能性サービス






From: Bldg-sim <bldg-sim-bounces at lists.onebuilding.org <mailto:bldg-sim-bounces at lists.onebuilding.org> > On Behalf Of Chris Yates via Bldg-sim
Sent: Tuesday, January 19, 2021 7:16 PM
To: 'David Eldridge' <DEldridge at grummanbutkus.com <mailto:DEldridge at grummanbutkus.com> >; 'Jim Dirkes' <jvdirkes2 at protonmail.com <mailto:jvdirkes2 at protonmail.com> >; bldg-sim at onebuilding.org <mailto:bldg-sim at onebuilding.org> 
Subject: Re: [Bldg-sim] exhaust air liquid heat recovery loop



Hi David,


Yes. Exactly. Dehum is also a good use-case as well, requiring simultaneous cooling and heating – which the heat pump gives.


At the bottom of https://www.konvekta.ch/network-recovery-systems.html <https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.konvekta.ch%2Fnetwork-recovery-systems.html&data=04%7C01%7CNicholas.Caton%40se.com%7Cc199e06cf5414ff1712308d8bc634c4a%7C6e51e1adc54b4b39b5980ffe9ae68fef%7C0%7C0%7C637466481990230084%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=tULjb3HwWL%2FCUIF3voPBeQYRlqwb3m1EXUHibsLa9mg%3D&reserved=0>  “Konvekta uses the DOE-2 building simulation software as a basis to design an energy recovery system.”.


In terms of buildings, I was actually presenting this as a bit of a “blue sky” option for some older hospital estates that we’re doing some front end strategy work for. Many of the current systems use RAR coils. However, most have no heat recovery at all and we’re considering how to retrofit it without reworking duct routes to accommodate S&E air-handlers with plate heat recovery.


I’ve seen this kind of system on laboratory jobs more recently, but not in hospitals or in a retrofit context.


Kind regards




From: David Eldridge <DEldridge at grummanbutkus.com <mailto:DEldridge at grummanbutkus.com> > 
Sent: 19 January 2021 03:06
To: chris.malcolm.yates at gmail.com <mailto:chris.malcolm.yates at gmail.com> ; 'Jim Dirkes' <jvdirkes2 at protonmail.com <mailto:jvdirkes2 at protonmail.com> >; bldg-sim at onebuilding.org <mailto:bldg-sim at onebuilding.org> 
Subject: RE: [Bldg-sim] exhaust air liquid heat recovery loop


Chris, I’m sorry I didn’t quite understand your scenario before. Something like this, except it would be a heat pump to make hot and cold

Integrated Chiller - Konvekta AG <https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.konvekta.ch%2Fintegrated-chiller.html&data=04%7C01%7CNicholas.Caton%40se.com%7Cc199e06cf5414ff1712308d8bc634c4a%7C6e51e1adc54b4b39b5980ffe9ae68fef%7C0%7C0%7C637466481990230084%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=KXR3neHIQP4ptf%2BgqHoEE8E1r%2FfFU8ptLclyqJGMxaQ%3D&reserved=0> 


We’re primarily seeing the runaround type or plate-and-frame direct heat exchange instead of using a heat pump to boost the temperatures, although I can see some appeal.


What type of buildings are you looking at this for?





David S. Eldridge, Jr., P.E., BEMP, BEAP, HBDP, GGA



Direct: (847) 316-9224 | Mobile: (773) 490-5038


Grumman/Butkus Associates | 820 Davis Street, Suite 300 | Evanston, IL 60201

Energy Efficiency Consultants and Sustainable Design Engineers


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From: Bldg-sim <bldg-sim-bounces at lists.onebuilding.org <mailto:bldg-sim-bounces at lists.onebuilding.org> > On Behalf Of Chris Yates via Bldg-sim
Sent: Monday, January 18, 2021 6:29 AM
To: 'Jim Dirkes' <jvdirkes2 at protonmail.com <mailto:jvdirkes2 at protonmail.com> >
Cc: bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org> 
Subject: Re: [Bldg-sim] exhaust air liquid heat recovery loop


Hi Jim,


In a generic sense, this is one of a number of different systems that capture exhaust heat via a coil in the exhaust. In the list below I am trying to establish if anybody has 


Similar systems


1.	We’ve already seen run-a-round coils described
2.	Exhaust air heat pumps have been a very common system for residential. They tend to use the refrigerant as the heat transfer medium. Some manufacturers of these units are :

a.	 <https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ivprodukt.com%2Fproducts%2Fhome-concept-ecoheater&data=04%7C01%7CNicholas.Caton%40se.com%7Cc199e06cf5414ff1712308d8bc634c4a%7C6e51e1adc54b4b39b5980ffe9ae68fef%7C0%7C0%7C637466481990249997%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=D8jubNzzFj2TrVcF5Fdh9wRiP9JUqM5OT20GRJlHks4%3D&reserved=0> https://www.ivprodukt.com/products/home-concept-ecoheater 
b.	 <https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.nibe.eu%2Fen-eu%2Fproducts%2Fheat-pumps%2Fexhaust-air-heat-pumps%2FNIBE-F750-_-237&data=04%7C01%7CNicholas.Caton%40se.com%7Cc199e06cf5414ff1712308d8bc634c4a%7C6e51e1adc54b4b39b5980ffe9ae68fef%7C0%7C0%7C637466481990249997%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=sBEsWYxesbMlmJy9lcFsRiRVzVNa%2FhLGp1UgqLA9JFU%3D&reserved=0> https://www.nibe.eu/en-eu/products/heat-pumps/exhaust-air-heat-pumps/NIBE-F750-_-237

3.	Supply and extract air handling with integrated heat pump augmenting (straddling) a plate or wheel heat exchanger. They tend to use the refrigerant as the heat transfer medium. Some manufacturers of these units are :

a.	 <https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.genvex.com%2Fen%2Fproducts%2Fair-ventilation---air-heat-pump%2Fpremium-preheat-500&data=04%7C01%7CNicholas.Caton%40se.com%7Cc199e06cf5414ff1712308d8bc634c4a%7C6e51e1adc54b4b39b5980ffe9ae68fef%7C0%7C0%7C637466481990259951%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=vjOvLS4qAQOHbDJbN6w47kOWasPNnVj6DABy2m%2F0Fiw%3D&reserved=0> https://www.genvex.com/en/products/air-ventilation---air-heat-pump/premium-preheat-500
b.	 <https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DhzVOTjH_GIg%26feature%3Demb_logo%26ab_channel%3DFl%25C3%25A4ktGroup&data=04%7C01%7CNicholas.Caton%40se.com%7Cc199e06cf5414ff1712308d8bc634c4a%7C6e51e1adc54b4b39b5980ffe9ae68fef%7C0%7C0%7C637466481990259951%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=fbzfFgQZCRYX3ZFQFTRrYIuhMq5mMOVlRav6GrEwpUQ%3D&reserved=0> https://www.youtube.com/watch?v=hzVOTjH_GIg&feature=emb_logo&ab_channel=Fl%C3%A4ktGroup


The system I’m describing

The heat transfer medium is water or brine (like the RAR coil), but this is piped to a compressor remote from the AHU. The attached is a crude mock-up of such a system using IDA’s ESBO interface (this has not been validated). Apart from a gas boiler for top-up heating, it would be an “all-electric” system. Britain and Scandinavia both have relatively low carbon electricity now. The fact that recovered heat can be re-used in a very general purpose way at a potentially high COP is quite an attractive idea. We may even pre-heat service hot water. Note also that the sum of UA for all the heaters in the zones will be much bigger than the heater coil’s UA in the AHU itself (meaning supplied heat can be a lower grade). It may also remove some of the perceived penalties of reheat (i.e. heat pumps simultaneously make both cold and heat).


I’m searching for an appropriate quote…


There are two major products that came out of Berkeley: LSD and UNIX. We don't believe this to be a coincidence.






From: Jim Dirkes <jvdirkes2 at protonmail.com <mailto:jvdirkes2 at protonmail.com> > 
Sent: 15 January 2021 21:44
To: chris.malcolm.yates at gmail.com <mailto:chris.malcolm.yates at gmail.com> 
Cc: bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org> 
Subject: Re: [Bldg-sim] exhaust air liquid heat recovery loop



I don't think I understand the system....

That clearly means it's not something common for my portion of the world!

On the other hand, it sounds no different than energy recovery - can you clarify a bit, please?


… The world is having a crisis of reason. I don’t think the world is  having a crisis of faith. If anything, there is plenty of faith around, in both good and bad things. In some ways, there is altogether too much faith, and too little reason.

Jim Dirkes  1631 Acacia Drive NW Grand Rapids, MI 616 450 8653




‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐

On Friday, January 15, 2021 8:39 AM, Chris Yates via Bldg-sim < <mailto:bldg-sim at lists.onebuilding.org> bldg-sim at lists.onebuilding.org> wrote:


Hi all,


I will resist the temptation to say “happy” new year. Perhaps, for 2021, the expression “moderately relieved” new year is more appropriate (it’s certainly more British). I hope as many of you as possible have avoided covid. I know there are some members of this list who have not been so fortunate. God speed your recovery.


In IDA ICE, there is an option to model a liquid heat recovery loop in the exhaust of an air handling unit (image attached). In essence, this is just putting a cooling coil in the exhaust. Heating, including heat recovery, is after all as much a cooling process as it is a heating process. This cooling coil can then integrate with some form of heat recovery/ reversible chiller – a bit like a run-a-round coil heat recovery on steroids!


This works in theory. However, I was just wondering how prevalent it is in practice. Would I be naïve to present this as an option to clients? I know I’ve not come across this in the UK. Is it just a Scandinavian thing?


I’d be very grateful to hear of any projects that have successfully (or unsuccessfully!) integrated heat recovery via exhaust air liquid loops.


It seems to me that the benefits could be manifold:

*	“decoupling”: Heat recovery potential increases as the building gets warm, but with traditional plate or thermal wheel heat recovery the demand for it simultaneously decreases. By buffering the heat to water, or re-directing it elsewhere (e.g. SHW) heat recovery becomes more general purpose.
*	A useful load for the chiller during periods of low chiller load. There are well understood problems with chillers cycling on/off during periods of low load – aka “low delta T syndrowm”. By dual purposing chiller equipment for heat recovery, it provides a stable baseload for chillers during these periods.


Kind regards




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