[Bldg-sim] exhaust air liquid heat recovery loop

Fred Betz fbetz at aeieng.com
Wed Jan 20 07:34:08 PST 2021


This is a similar product that we used in a hospital in Germany that I’m told are very common.

It’s worth noting in Germany hospitals are 100% outside so they are more laboratory like, but in general move less total air than US hospitals.

I don’t think the FW product is quite as efficient as the Konvekta solution, but it’s cheaper.

[Doing this from memory from ~4 years ago] Per regulations in Germany I believe air-side heat recovery effectiveness needs to be above 60% or 65% so a standard run around loop won’t achieve that. There’s also regulations regarding heat recovered per unit fan energy used so you’re not chewing up all your savings with static pressure.

Not sure how uniform Europeans are on their energy code from country to country.

AEI has done the system you’re describing in laboratories several years back with a field built solution tying in the condenser or evaporator side of the heat pump into the run around loop depending on climate and load profile. It was pretty effective in places like San Francisco, Washington DC, etc. [not extremely hot or cold] so you get more run hours out the RAL due to better approach temperatures and can support process cooling or reheat. I modeled this in TRNSYS as eQUEST doesn’t bend that way. We weren’t really using e+ back then so I didn’t try this configuration in that software.

Getting the controls to work in the field was another matter so there’s a lot of benefit to a packaged solution like the ones identified in this thread. You can then integrate the heat pump anywhere in the chilled/hot water loops (assuming appropriate temperatures) and the heat recovery controller will dispatch according to what’s best for the RAL while loading the heat pump or heat recovery chiller as needed.

Hope that helps.


Fred Betz PhD, LEED® AP BD+C
Building Performance
O: 608-238-2616 / D: 608-236-1175
Affiliated Engineers, Inc.<https://aeieng.com/>
5802 Research Park Boulevard | Madison, WI 53719

From: chris.malcolm.yates at gmail.com <chris.malcolm.yates at gmail.com>
Sent: Tuesday, January 19, 2021 4:16 AM
To: '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

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 “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://www.konvekta.ch/integrated-chiller.html>

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

grummanbutkus.com<http://grummanbutkus.com/> | Blog<http://grummanbutkus.com/blog> | Facebook<https://www.facebook.com/pages/GrummanButkus-Associates/1385285015032526> | Twitter<https://twitter.com/grummanbutkus>

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 :
     *   https://www.ivprodukt.com/products/home-concept-ecoheater
     *   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 :
     *   https://www.genvex.com/en/products/air-ventilation---air-heat-pump/premium-preheat-500
     *   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 <bldg-sim at lists.onebuilding.org<mailto: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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