How can I put air con onto a mvhr ductwork?

[Kelvin]

Just now, PeterW said:

If it is very cold you may find your ducting has contracted to the point that it’s barely visible … 

You make un assumption it’d much different in the summer

[Kelvin]

3 minutes ago, Nickfromwales said:

Good lad. We will  not, of course, accept your word for it. Please post photos here for "authentication". We will make allowances for it being cold when we score you.  

Don't forget to insulate them. You never know when you'll need to add "air con" ( not cooling ) from an A2W HP

Will do
 

I shall place a tray of ice by an open window on a hot day. 

[Nickfromwales]

3 minutes ago, Kelvin said:

I shall place a tray of ice by an open window on a hot day.

The perfect solution to the OP's issue? 

 

The job's yours  . Let me show you to your office.

[Mike]

There is another product on the market - or rather two products, once for cooling, the other for humidifying - specifically designed for MVHR use, from HomEvap. As noted above, the low airflow in MVHR systems means that the effect will be modest, though so will the cost of running it.

 

The cooler works by humidifying the extract air just before the heat exchanger, dropping the temperature through evaporation, which then cools the incoming air by a few degrees, with no need for a separate chiller unit. I'm hoping to install one later this year.

 

The humidifier is fitted on the supply side.

 

In the UK you can buy a Blauberg branded version of the cooler, albeit at a premium price. They may sell you the humidifier too, otherwise you'll need to find an EU supplier prepared to ship them to the UK.

 

 

 

 

[Dan F]

18 hours ago, Petrochemicals said:

 

To be perfectly honest I'm willing to give it a go, the noise is acceptable during the day for those few days, obviously it would have to go off at night which is not ideal, but the portable one I have at present has to go off at night because of the noise, it works by swallowing inside air, spitting half out hot to the outside and half out cold to the inside, thus meaning you are drawing air in from the outside anyway. 

 

The pipes are insulated all the way to the outside, condensation isn't an issue for a few days anyway, especially when the loft will be somewhere around 35c. 

 

I already gave it a go (Passivhaus with automated external shading) but probably wouldn't do it again, to be honest.  I've posted about it elsewhere but the effectiveness is fairly poor even with MVHR on boost.

 

While it's not immediately apparent, there are a couple of issues with the manufacturer-supplied cooling power data to be aware of:

- It assumes air into Comfopost is 27C, but if you are keeping the house at a reasonable temperature and have an efficient MVHR it will never be 27C.

- With an A/C or fan-coil unit, you are recirculating the air in the house so the kW quoted is what you get.  With an MVHR on boost with a Comfopost a portion of the quoted kW goes into cooling the incoming air (which you are now bringing in at a faster rate) and only the remaining cooling power actually acts to reduce the temperature in the house.

 

Let me know if you want any further details.

 

 

[Petrochemicals]

On 14/02/2023 at 08:49, jack said:

 

 

8 hours ago, Nickfromwales said:

Not that I care to waste any of my valuable personal time responding to such a nonsense response, but what exactly do you consider "rude".

I asked you two very simple questions, and, if you want help, maybe you should read between the lines and answer them so you can receive said help.

 

Folk on here reply to help people for free, on a forum which is free to join, so, IF you wish to jump down, momentarily, off the highest horse I've seen for quite some time, I would be happy to answer you questions.

 

For definition;

A "moron" would install a system which was not properly designed and installed as fit for purpose, so if I was the kind of person to make any assumptions or be "rude" to you, my question in my first reply would have read "What MORON designed this system where they didn't define the parameters or install it fit for purpose?", and then, referring to someone as a moron would be fine and appropriate. 👍 For further clarity, I am NOT referring to you as the moron, yet, as I do not know if you were said moron or not. Once I have ascertained who the moron actually is, then I will engage, with all of my many years of dealing with morons, my retort.

 

 Usage of Moron

 

The terms idiot, imbecile, moron, and their derivatives were formerly used as technical descriptors in medical, educational, and regulatory contexts. These uses were broadly rejected by the close of the 20th century and are now considered offensive.

 

As we like to offer comprehensive replies here at Buildhub, please be aware that, rather embarrassingly, your attempt to insult me is actually about a century out of date. You may need to go to another forum to get some up to date material. 

 

OK, so lets assume you did come here fore free help, I will rephrase my questions to you as follows.

 

 

Should have read;

Please could you tell me if the already installed ductwork has been insulated?

Are you aware that there is a huge difference between air con and cooling?

 

There you go, and hopefully this makes up for me upsetting you so much by trying to help you, for free, in my spare time. Please also be aware, that If you can't get a reasonably speedy and satisfactory answer here, then please go and employ a system designer, who will take money from you in return for the answers you seek.

 

Kind regards, Nick.

Yep, read it all, cheers! lockquote widblockquote widglockquote widlockquote widget

Edited March 11, 2023 by Petrochemicals

[Petrochemicals]

3 hours ago, Dan F said:

 

I already gave it a go (Passivhaus with automated external shading) but probably wouldn't do it again, to be honest.  I've posted about it elsewhere but the effectiveness is fairly poor even with MVHR on boost.

 

While it's not immediately apparent, there are a couple of issues with the manufacturer-supplied cooling power data to be aware of:

- It assumes air into Comfopost is 27C, but if you are keeping the house at a reasonable temperature and have an efficient MVHR it will never be 27C.

- With an A/C or fan-coil unit, you are recirculating the air in the house so the kW quoted is what you get.  With an MVHR on boost with a Comfopost a portion of the quoted kW goes into cooling the incoming air (which you are now bringing in at a faster rate) and only the remaining cooling power actually acts to reduce the temperature in the house.

 

Let me know if you want any further details.

 

 

That did alarm me, the fact that new air is coming in at outdoor temperature, last summer that would have been 500m3 per hour of 39c air, on boost or 100m3 on normal. I've a portable air con that does a similar, splitting the interior air half and half, it seemed to work, but there is a cut off point, if the out air is 16 the room is 26 any hotter than 36 and it is not doing anything. 

 

At the moment 

[Petrochemicals]

3 hours ago, Mike said:

There is another product on the market - or rather two products, once for cooling, the other for humidifying - specifically designed for MVHR use, from HomEvap. As noted above, the low airflow in MVHR systems means that the effect will be modest, though so will the cost of running it.

 

The cooler works by humidifying the extract air just before the heat exchanger, dropping the temperature through evaporation, which then cools the incoming air by a few degrees, with no need for a separate chiller unit. I'm hoping to install one later this year.

 

The humidifier is fitted on the supply side.

 

In the UK you can buy a Blauberg branded version of the cooler, albeit at a premium price. They may sell you the humidifier too, otherwise you'll need to find an EU supplier prepared to ship them to the UK.

 

 

 

 

Its worth a shot, other wise the mvhr is being switched off in the heat and I'll stick with the portable., it does however mean getting water to the loft. It is just to trim the heat from the incoming air for those few days. 

[JohnMo]

I looked at homevap, and it's same with all evaporative cooling products for the UK, they don't work well in a high humidity climate, because the air isn't that from saturation already.

 

I would do your research before spending

[andyj007]

did an experament of pumping cold air through my mvhr ductwork on my last house ,  I spliced the flow pipes  in the loft and pushed through cooled air from a nearby air con.. via a cardboard capture  tent and ductwork to see if it would work  

it created a lot of condensation on the outside of ductwork, and wasnt all that effective.  .  , 

when i designed this new house we are in, decided that 3 dedicated air condition units in stratigic  places was a far better and cheaper option than insulating all the ductwork  for a sub optimal system.. As a bonus in winter if needed they can be used as heaters .

you can buy you own split system air con systems and fit your self for a little under 500 pounds,,  ive fitted many of these  for family and freinds , from my experiance thats where i would  put my money every time 

 

Edited March 11, 2023 by andyj007

[Mike]

23 minutes ago, andyj007 said:

you can buy you own split system air con systems and fit your self for a little under 500 pounds

Undoubtedly the best solution where feasible.

[Petrochemicals]

Thanks for the replies, split unit it is. Just seems like a bother you can't just stick a small one on and utilise the ductwork. 

[Dan F]

16 hours ago, Petrochemicals said:

That did alarm me, the fact that new air is coming in at outdoor temperature, last summer that would have been 500m3 per hour of 39c air, on boost or 100m3 on normal.

It doesn't come in at 39C.  If the internal temperature is 21C and MVHR is 90% efficient it comes in at 23C.  23C is better than 39C but:

- You need more cooling power to cool incoming 23C (that you are now bringing in faster due to boost) than you do to cool existing 21C air in the room.

- The Comfopost power figures assume 27C.  If the air is 23C and not 27C then power is only going to 80% of that stated.

 

If you don't want to use split-unit and want to use ASHP (that you may be using for heating/DHW), then fan-coil units are the answer.

[Dave Jones]

could a standard spilt system internal unit be plumbed to a normal ASHP running in reverse so you have have mvhr cooling, ufh cooling and a blower or 2 as well ?

[joth]

14 minutes ago, Dave Jones said:

could a standard spilt system internal unit be plumbed to a normal ASHP running in reverse so you have have mvhr cooling, ufh cooling and a blower or 2 as well ?

I think you're reinventing the water to air fan coil unit (FCU), as discussed many times on this forum.

 

A standard split a/c indoor unit won't work as it requires refrigerant rather than cold water. An FCU is much simpler device as it's just a water pipe running through a heat exchanger.

Edited March 12, 2023 by joth

[joth]

12 hours ago, Petrochemicals said:

Thanks for the replies, split unit it is. Just seems like a bother you can't just stick a small one on and utilise the ductwork. 

Try thinking about it the other way around: install super sized (200mm) ducting for the a/c unit for each room, working in recirculating fashion, and once you have that in place it's fairly simple to feed the MVHR to the air intake for it to also use it's ductwork to supply fresh air too.

This is how pretty much every modern commercial/office HVAC is designed.

 

By analogy: design a road network  for heavy goods vehicles and they can take the odd motorbike too with little effort. But design the roads with only motorbikes in mind, and you're going to have a bad time trying to squeeze and fleet of HGVs down it.

 

[Dave Jones]

27 minutes ago, joth said:

I think you're reinventing the water to air fan coil unit (FCU), as discussed many times on this forum.

 

A standard split a/c indoor unit won't work as it requires refrigerant rather than cold water. An FCU is much simpler device as it's just a water pipe running through a heat exchanger.

 

interesting, is there an off the shelf setup with an integral blower ? I'd like to mount one in the landing so it could cool the a large area

 

thanks

[joth]

19 minutes ago, Dave Jones said:

 

interesting, is there an off the shelf setup with an integral blower ? I'd like to mount one in the landing so it could cool the a large area

 

thanks

Checkout

 

https://www.saturnsales.co.uk/Panasonic-Aquarea-PAW-FC2A-Ducted Fan Coils.html has FCU up to 8kW cooling capacity, which should be good for a large area 

 

 

[Dave Jones]

11 minutes ago, joth said:

Checkout

 

https://www.saturnsales.co.uk/Panasonic-Aquarea-PAW-FC2A-Ducted Fan Coils.html has FCU up to 8kW cooling capacity, which should be good for a large area 

 

 

perfect thanks.

[Petrochemicals]

4 hours ago, Dan F said:

It doesn't come in at 39C.  If the internal temperature is 21C and MVHR is 90% efficient it comes in at 23C.  23C is better than 39C but:

- You need more cooling power to cool incoming 23C (that you are now bringing in faster due to boost) than you do to cool existing 21C air in the room.

- The Comfopost power figures assume 27C.  If the air is 23C and not 27C then power is only going to 80% of that stated.

 

If you don't want to use split-unit and want to use ASHP (that you may be using for heating/DHW), then fan-coil units are the answer.

I did not know mvhr reverse exchanged it of the outside air was warmer than required, I though the Auto bypass thing just shunted the air past the heat exchanger. 

[Petrochemicals]

4 hours ago, Dave Jones said:

could a standard spilt system internal unit be plumbed to a normal ASHP running in reverse so you have have mvhr cooling, ufh cooling and a blower or 2 as well ?

As far as I can tell yes as they call the ashp an"inverter" in the wall units. But I do not know how easy it would be integrating it into an existing system that does hot water. 

[Petrochemicals]

5 hours ago, joth said:

Try thinking about it the other way around: install super sized (200mm) ducting for the a/c unit for each room, working in recirculating fashion, and once you have that in place it's fairly simple to feed the MVHR to the air intake for it to also use it's ductwork to supply fresh air too.

This is how pretty much every modern commercial/office HVAC is designed.

 

By analogy: design a road network  for heavy goods vehicles and they can take the odd motorbike too with little effort. But design the roads with only motorbikes in mind, and you're going to have a bad time trying to squeeze and fleet of HGVs down it.

 

That's not beyond reason but it would mean throwing away 200 quids worth of semi flex. I would not need to put round 200mm throughout would I just on the main supply duct? Or does that need to be bigger? This is a mid 70s build house that they put a hot air heater system on. The heating system was replaced due to it being hideously in efficient but the space remains to stick in whatever duct work is nececerry. Part of the reason for putting in the mvhr unit wat that there where 2 double air bricks and a single in the house all installed in the kitchen, the rest of the house was obviously vented at sometime by the hot air system, but since that has been removed the rooms can get stuffy, especially the down stairs living room which has no chimney effect on it at all. It had to be a ventilation system, so I thought why not a mvhr unit, get rid of the kitchen extractor and toilet fan and get rid of the cold pooling and condensation along with the fresh air input. 

[TerryE]

On 10/03/2023 at 19:14, Petrochemicals said:

Well I have only just joined, and 2 rude replies, are you the local moron? 

 

On 10/03/2023 at 19:30, Petrochemicals said:

And you are one of the brownest noses. In what way does his reply justify your reply?

 

I browsed the topic and on reading @Nickfromwales first post, my honest reaction was that they were reasonable scoping Qs aimed at focusing the discussion into something valuable for you.  You have now twice replied by trolling in response to reasonable points.  Not a good start for a new member.

[joth]

1 hour ago, Petrochemicals said:

I would not need to put round 200mm throughout would I just on the main supply duct? Or does that need to be bigger?

 

Neither.

Ignore everything you already have purchased/acquired/done.

First design from scratch a (recirculating) cooling system that would work well as cooling system. Then see if any part of it can be utilised as a fresh air supply too.

 

You're far too deeply committed to prior decisions for this to be a realistic proposal now, but it's the real answer to your lamentation about not being able to share one set of ducting for 2 proposes.

DW I too made the same "mistake", so now have 2 separate sets of ducts into rooms with a cool air supply.

 

[Nickfromwales]

6 hours ago, TerryE said:

 

 

I browsed the topic and on reading @Nickfromwales first post, my honest reaction was that they were reasonable scoping Qs aimed at focusing the discussion into something valuable for you.  You have now twice replied by trolling in response to reasonable points.  Not a good start for a new member.

Yup. Relegated to the "cock-womble" shelf. I would say a "moron", but don't wish to fall onto my own sword lol. At least I can't hang myself......as I've just been to the rope shop and it's just all recently been snapped up by someone.