MVHR - Geothermal Brine Heat Exchanger

[Barney12]

In my continuing research of cooling options I came across these as a heating/cooling option add on for MHRV. 

Ive found a couple of options:

 

Systemair: Link

 Zehnder Comfo: Example

 

and a unit from BPC which they seem to say is an Airflow product but I can find no reference to it anywhere and the picture shows a Helios badge: Link

 

Does anyone have any views? 

If I decide quickly it wouldn't be impossible for me to integrate a small brine loop in the groundworks that start on Monday.

Edited April 18, 2017 by Barney12

[SteamyTea]

Can't you just stick a cheap portable aircon unit onto the MVHR inlet to the rooms.

[Barney12]

1 minute ago, SteamyTea said:

Can't you just stick a cheap portable aircon unit onto the MVHR inlet to the rooms.

 

Our MVHR is in the loft so that's not really practical. Plus I don't really want anything too ad hoc.

I have looked at duct based split aircon units but couldn't fathom if they could sit inline with an MHRV unit. I have a feeling they would play hell with flow rates?

[SteamyTea]

Would you have to be concerned with flow rates in the summer?

I often wonder how well balanced a system is after a few weeks of operation.

[MikeSharp01]

13 hours ago, SteamyTea said:

I often wonder how well balanced a system is after a few weeks of operation.

What makes you wonder Steamy?

[Barney12]

Just to update. I've attached the spec document from BPC for their Geothermal unit. 

 

Alas the specs recommend insulated ducting to prevent condensation forming which makes things difficult for me as I don't have enough free space for that size duct. 

 

Although I'm not convinced that's a real world issue in our climate? Any thoughts? I've asked BPC to confirm what their normal specification is. 

 

Airflow+Ground+to+Air+exchanger.pdf

[SteamyTea]

9 hours ago, MikeSharp01 said:

What makes you wonder Steamy?

Just that when people are actually living in a place, habits change.  So doors may be left open a bit, windows not fully closed, filters block up at different rates, all sorts of 'other things' go on.

 

[MikeSharp01]

36 minutes ago, SteamyTea said:

Just that when people are actually living in a place, habits change.  So doors may be left open a bit, windows not fully closed, filters block up at different rates, all sorts of 'other things' go on.

Makes sense but would need more work on quantification, need to experiment once we get a system up and running.

Edited April 19, 2017 by MikeSharp01

[Barney12]

So after a lot of thinking/deliberating we decided to fit the geothermal heat exchanger. Just the small matter of digging a 50m trench 1.5m deep, 1.5m (ish) wide so we could run the 100m of 32mm pipe. 16 tonnes of sand to bed and cover. All done in one day.........exhausting! 

 

 

 

[Onoff]

The few on here who have sloping sites that need a lot of terracing etc.....is it I wonder worth laying geothermal pipe then just covering it over if your changing the landscape that much?

[SteamyTea]

Are you putting in a few temperature sensors? May make for useful data.

[Barney12]

Just now, SteamyTea said:

Are you putting in a few temperature sensors? May make for useful data.

 

I did consider it but simply ran out of time to order anything. 

From everything I've read we have excellent ground conditions for geothermal.

How effective the heat exchanger will be is a complete unknown. I'm mainly interested in the cooling rather than heating.

This decsion has been my first "gamble".

[Barney12]

12 minutes ago, Onoff said:

The few on here who have sloping sites that need a lot of terracing etc.....is it I wonder worth laying geothermal pipe then just covering it over if your changing the landscape that much?

 

Dont underestimate the cost of bedding the pipe properly in sand. I wouldn't want to be spending hundreds of pounds on sand bedding for something I "might" use.

[Nickfromwales]

13 hours ago, Barney12 said:

So after a lot of thinking/deliberating we decided to fit the geothermal heat exchanger. Just the small matter of digging a 50m trench 1.5m deep, 1.5m (ish) wide so we could run the 100m of 32mm pipe. 16 tonnes of sand to bed and cover. All done in one day.........exhausting! 

 

 

 

Balls of steel ??

[SteamyTea]

12 hours ago, Nickfromwales said:

Balls of steel

Must be a couple of achers

[Declan52]

You know how dangerous that is with all the spoil sitting so close to the trench edge. ESP with the first metre of that being made ground. That guy would be squeezed before he had time to say wdf.

[Nickfromwales]

3 minutes ago, Declan52 said:

You know how dangerous that is with all the spoil sitting so close to the trench edge. ESP with the first metre of that being made ground. That guy would be squeezed before he had time to say wdf.

C'mon, at least it wasn't raining. . 

[Lots2learn]

Hi All

I’m new to this website and to self build. I am trying to establish how effective ground heat exchange is for MVHR systems such as is offered by Airflow. After the recent spell of really hot weather could anyone who has a system fitted give me some feedback. 

Thanks

[Jeremy Harris]

On 30/07/2018 at 16:31, Lots2learn said:

Hi All

I’m new to this website and to self build. I am trying to establish how effective ground heat exchange is for MVHR systems such as is offered by Airflow. After the recent spell of really hot weather could anyone who has a system fitted give me some feedback. 

Thanks

 

Essentially it's a very, very dodgy area in the UK climate.  The reasons are to do with keeping the ground heat exchange ducts free from mould and fungal growth for decades.  At least one house in Belgium has been made uninhabitable by a poor choice of duct for their MVHR (worth a read): https://www.greenbuildingadvisor.com/article/belgian-passivhaus-is-rendered-uninhabitable-by-bad-indoor-air

 

There are a couple of companies that offer silver-coated ground ducts, to try and prevent mould growth, but they are expensive and (as a scientist) I'm no convinced of their long term reliability.  I personally like "permanent" house systems to have a life of several decades, as the last thing I want to do is have to dig up an established garden a few years later.

[Lots2learn]

Thanks @JSHarris. I presume this problem only applies to earth pipe systems rather than brine filled ones. In any case I think we have decided to ditch this idea. The roof skylights will be openable to increase ventilation during the hottest days and we have shading for the glazing on the south elevation. 

[Dreadnaught]

On 30/07/2018 at 16:31, Lots2learn said:

Hi All

I’m new to this website and to self build. I am trying to establish how effective ground heat exchange is for MVHR systems such as is offered by Airflow. After the recent spell of really hot weather could anyone who has a system fitted give me some feedback. 

Thanks

 

Why would you want to pre-warm the air through the ground? @JSHarris points are well made. An alternative if you can really justify the expense might be a brine loop system? But as you are going for a near passive house levels of insulation, your heat demand will be very low so I suspect you wont be able to justify the expense.

[Jeremy Harris]

1 minute ago, Lots2learn said:

Thanks @JSHarris. I presume this problem only applies to earth pipe systems rather than brine filled ones. In any case I think we have decided to ditch this idea. The roof skylights will be openable to increase ventilation during the hottest days and we have shading for the glazing on the south elevation. 

 

 

Yes, it is an earth pipe problem  Brine systems can be made to work OK, but need a lot of ground works.  We've found that just using a relatively cheap ASHP and using it for the UFH in winter and then switching it to cooling mode to cool the floor in hot weather works very well (our build isn't PHI certified, but exceeds the PH standard).

[Lots2learn]

@Dreadnaught the application is more for the cooling effect in summer although it has some pre warming effect in the winter as well. I think having researched this further it might not be for us. @JSHarris I have been told that because we are on mains gas ASHP is not a worthwhile investment, would you agree?

[Jeremy Harris]

10 minutes ago, Lots2learn said:

@JSHarris I have been told that because we are on mains gas ASHP is not a worthwhile investment, would you agree?

 

 

Yes, definitely.  It only makes sense for us to use an ASHP because we stuck with only having electricity, plus we have a fair bit of PV, so summer cooling using the ASHP is almost always "free",

 

You just need to weigh up the capital cost of the brine loop cooling versus it's effectiveness, which is unlikely to be very good.  You may want to consider a cheap air-to-air heat pump to address cooling, as opening windows won't help at all when the outside air temperature is warmer than your desired room temperature.  Air-to-air heat pumps are pretty cheap and if designed needn't cost a lot to install.

[Nickfromwales]

If you dont have an ASHP and want a system to provide 'active cooling' then a brine loop, if correctly installed, should make a difference. With a thin line between success and failure the correct disciplines for setting the pipe and the depth at which its set are critical and need to be fully observed. 

If you can get reliable flow temps of sub 12^oC then on a very hot day that will provide some reduction in the incoming airflow, but I'm currently looking into the merits of doubling up or seriously oversizing the heat battery ( wet duct heater ( or cooler )) to maximise the effect and remove every ounce of heat energy from the brine loop recirculation.