air circuloation via ducting in large unheated room

[Chris Hogg]

As I may have mentioned before, I volunteer at my local Archive. We have a large room where we do our research etc. for enquirers, with rows of shelves stacked with ring-folders, books, files etc. It is cold in winter, and the humidity is much higher than that recommended for document storage. The dimensions of the room are 12.2 x 8.35 x

4.84 metres (l x w x h), giving a volume of 493 cu. metres; call it 500 cu. metres. The cost of heating this room is getting exorbitant, may be beyond our means, and we are looking into ways of making it cheaper.

When I was gainfully employed, we had a large aircraft-hanger-like lab that housed big items for chemical engineering research and pilot scale development, probably several times the size of the research room at the Archive. It was heated by industrial space heaters which were expensive to run, although I can't now remember if they were gas-fired or electric. Then someone pointed out that most of the warm air went straight up to the roof, and they had the bright idea of drawing it back down through ducting, and recirculating it at floor level. This was very simply and cheaply done using a few lengths of drainage pipe stacked vertically and a duct fan at the bottom to draw the air down. Apparently it was a great success, but I have no details.

I have been wondering if we might use something similar at the Archive. Does anyone have any experience of this sort of thing?

[Adrian Caspersz]

No experience, but after watching a few YT vids from my armchair (that need debunking, the vids not my arm...) it seams ye need to expel that air, and draw in drier air which on some days can come from outside. Otherwise use a dehumidifier to remove the water content, or find out where the water content is coming from. Exterminate people and plants.

Heating damp air is difficult and expensive.

[Martin Brown]

I think you best bet might be to use a dehumidifier rather than trying to heat it. Is the room really 5m high? Any chance of a false ceiling?

That or merely a big slow fan at the top to keep the air moving and prevent warm air trapping against the ceiling.

Is the moisture coming from the users of the archive?

It might work if you are losing a lot of heat upwards.

Our VH has 3m ceilings and warms up from the ceiling downwards. It greatly increases the cost to heat it and the floor is always cold.

You get no benefit from the convection heaters at all until the room has filled with warm air from the top down. Opening doors to let people in has obvious unwanted side effects (but not letting them in is worse).

[Andrew]

Large enough for properties up to 450 cubic metres and only costs £0.45 per day (but I think that must be way out of date !)

[www.GymRats.uk]

Suspended ceiling will significantly reduce heating costs. Our shop is around 9m x 5m with a high ceiling. I fitted a suspended ceiling dropping the height by about 1.5m and the combination of reduced room volume and new thermal thermal insulation afforded by the tiles made a huge difference to required thermal input.

As a quick and dirty fix to the space heating element I'd be inclined to take a look at those Chinese diesel heaters. Most manufacturers now do a "portable" unit around 5KW I beleive. Just need a something like a 25l jerry can and a wall through which the exhaust could be vented.

Just run it from a car battery and put it on trickle-charge over night.

20 Amp draw is only for start-up to heat glow plug, after that power consumption is very low.

[alan_m]

My dehumidifier is 300W on low and 580W on high and in a "damp" environment unlikely to auto switch off, assuming that water is continuously discharged out of the space.

It's very much like the adverts for electric blankets/throws. Only a few pence per night. Maybe true(ish) if switched on for 5 minutes to warm an bed which is insulated with a duvet but not if used as a throw wrapped around someone whilst watching tv in their unheated living room. The few pence per night figure is often repeated on social media, and in some crap main stream TV programs, when they are recommended in the latter application. Yes, they are a very much cheaper way to heat an individual but not a few pence per night.

[Theo]

We've discussed this before - there are two problems: the humidity and the fact that users are cold. They're related.

First of all, work out where the humidity is coming from. It may just be a result of the room being cold (as it cools, air holds less moisture, therefore relative humidity goes up). But it could be a roof/gutter leak, leaky pipe, rising damp from the floor, etc. Check that there isn't a source of moisture first of all.

If you want to reduce the humidity, you have to either dehumidify or increase the temperature. Both take energy.

For heating, what do you want to heat, the users or the documents?

A ducted system might help the users - duct heat to the research tables - but it won't help for bookshelves that aren't the focus of ducts.

If the problem is stratification - ie all the heat collecting at the top, like a convection oven - then some ceiling fans would help distribute it. You'll still be heating all that air, but at least it would spread the heat around.

Ducted fans won't be as good, because the fans are much less powerful. They would be find for focused heating (although so would other kinds of heaters) but not good for generally keeping the room dry.

An airtight suspended ceiling (even a giant plastic sheet) would reduce the volume of air you need to heat, which would keep everything warmer for less money.

Theo

[Theo]

Any combustion appliance will increase the amount of moisture in the room. So it would need to ensure that all combustion gases are vented outside.

(probably fine for the diesel heaters which need venting anyway, but some might be tempted by gas bottle heaters without external flue)

Theo

[The Natural Philosopher]

The physics of winter heating and humidity are that the outside air is cold that even when its raining by the time its been heated its pretty dry.

What would be ideal technically (no idea about practicality or cost) in this application is heat recovery ventilation - a sort of balanced flue with cold dry air being drawn down outside a concentric flue of hot air being expelled. This has the advantage it doesn't even need to be forced draught - hot air will escape yup the chimney so to speak as cold air that has been warmed a bit falls down from the other part of the flue

This wont eliminate heating needs, but will strongly reduce them

[Brian Gaff]

If you do not need the size then partition it off with insulated partitions and lease the other space off to somebody else?

Brian

[rick]

On one of the SelfBuild groups a guy detailed that he had a duct they ran from floor to ceiling and he had a low power fan sucking warm air down the duct and out at floor level .... he reckoned it saved him a lot on heating. Conversely in US whole house venting is popular, in upstairs landing ceiling there is a grill, which is the inlet to a box with motor actuated doors and 2 x fans. You press remote button ... and in loft pair of insulated doors open and fan starts to extract ... venting all hot air into loft .... which escape via roof vents. Massive saving on AC bill.

[SteveW]

Yes. I have a shed that is also a railway room and work room. It is insulated and I have an electric heater in there, but prefer not to use it much due to the cost and cooling is only by opening the door.

I have been meaning to get around to installing a fan, controlled as follows: If temperature is below setting and it is warmer outside, run the fan, extracting air from low level; if temperature is above setting and it is cooler outside, run the fan, extracting air from high level; if I press a button (because I am using paint or glue in there) run the fan, extracting air from both levels. In reality, two separate fans might make sense.

Other than for fume extraction, it would only probably useful for short periods of the year, but anything is better than nothing.

[Chris Hogg]

Thanks for the replies. As Theo said, it's been discussed before. I'm very familiar with many of the options - insulation - false ceiling - dehumidifier - etc. In the past I have and am again, monitoring the temperature and humidity with a data-logger to get actual numbers rather than relying on uninformed opinion expressed by our trustees.

But I particularly wanted to get people's views and experiences, if any, on the idea of sucking warm air down from the ceiling and 'recycling' it, as it were. Rick's first paragraph is the sort of thing I was looking for. Of course, it presupposes that there is warm air up under the ceiling in the first place.

One problem is that we don't own the building - we rent it. It's a schoolroom built onto the back of a church, and the church council are very reluctant to allow any modifications to the building in any form, which would include proper insulation, false ceilings, fans suspended from the ceiling, and exhaust-holes in walls. Apart from that, there would also be the expense, and the church mice are rich compared to what the Archive can afford.

[Theo]

Should probably add that, while a giant plastic sheet would prevent air rising, it would also introduce an interface between heated air (below) and unheated air (above). That would likely cause condensation on the plastic - and if the plastic is unevenly draped that might mean 'rain'. However you could use that to your advantage: have a smooth surface with one edge being lower, and install a gutter. You now have both heating and dehumidification :-)

(a fancier setup would have a second layer of breatheable membrane or something so that air can rise but drips can't fall)

Theo

[Thomas Prufer]

:-)

First: data-logger onna stick?

Thomas Prufer

[Chris Hogg]

Yep. Already been thinking about it. Needs a long stick. Probably several bamboo canes tied together.

[Martin Brown]

It would have to be externally vented. However, ad hoc flame based heating methods and libraries and archives do not sit well together.

I recall a terrifying barn heater device that was essentially a tall bottle of propane gas and pretty much the big flame thing off a hot air balloon but pointed horizontal. It did get the big space warm PDQ but it was alarming to watch in action!

The barn smelt of combustion products for a couple of hours afterwards.

[Thomas Prufer]

BTDTGTTTS. Duct tape! Overlap, wrap, done.

Or borrow a long fishing rod. These are telescoping cones, and the longer ones thus quite thick and sturdy in the 5 meter range.

Thomas Prufer

[Andrew]

Just seen an item on Merdian News about ?Bampton School where Downton Abbey/ITV filmed the series where it became the Downton Hospital used to rehabilitate WW1 soldiers.

It has now been renovated and it the local archive but the TV news shots showed electric storage rads in a building with solid cotswald stone walls, tall windows and steeply pitched ceiling with exposed oak trusses. Hope they put plenty of insulation in as part of the refurb.

[Andrew]

Here it is

Perhaps you could try and obtain a grant to insulate your building ?