[Bldg-sim] exhaust air liquid heat recovery loop

Mon Jan 18 04:28:58 PST 2021

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://www.ivprodukt.com/products/home-concept-ecoheater 
b.	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://www.genvex.com/en/products/air-ventilation---air-heat-pump/premium-preheat-500
b.	https://www.youtube.com/watch?v=hzVOTjH_GIg <https://www.youtube.com/watch?v=hzVOTjH_GIg&feature=emb_logo&ab_channel=Fl%C3%A4ktGroup> &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.

Cheers

Chris

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

Chris,

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

Chris

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