Basic principles of insulating things?.....and some queries I have for garage insulation

[kingofthehill]

I've been having some hair brained ideas for insulating my cheap steel slat garage roller door. I want to use the garage for odd jobs through the winters and the internal temperature is currently equal to the outside temperature which dipped to minus 6 this week and nearly killed me even though I was wearing 4 layers looking like Michelin Man!

The roof is fibreglass over osb2 board and will need insulating but I think the door is my biggest issue for starters. The roller at the top is not boxed in so it is impossible to heat the space because there is so much air flow coming in/going out. As well as this, the steel roller obviously gives no protection whatsoever in itself. This leads me to the following for discussion if you'd be so kind to indulge.....

To try and cut a long story short I want to try and insulate the whole area (the whole area floor to ceiling including the gap above the door) somewhat.

First I'd like to make sure that I understand how insulation works.....after some googling my understanding is that air is a poor conductor of heat and that it is a good thermal insulator in its own right. I also gather that having an air gap is all very well and good but if there is convection allowing air in and out of the cavity then warm air will always be able to escape from the space being heated, basically heat loss so heating the space is more difficult. So trapping the air and therefore stopping convection is the key which is why polystyrene foam (98% air) is a good insulator?

I'm tight so have been thinking of the cheapest way to tackle this. The door width is approximately 3m and about the same from floor to ceiling. I will need to easily open and close the insulating partition when a car is in situ. I want some sort of semi permanent construction that can either be removed in sections and stored overhead (something like 50cm wide panels) or a concertina type setup that can be hinged at one end of the door and pushed out of the way. I'm not too bothered if they aren't super solid so I am considering making relatively lightweight panels out of 25mm batten with 3mm hardboard sheets either side. I can figure out some system of mounting, hinging, latching etc but I'm considering filling the void in between the panels with polystyrene foam packing chips (packing peanuts) as I can buy enough of this material to fill the whole area for £12. Alternatively I have considered assembling the panels with sealant to trap air internally in the panels, would this have the same effect as filling with polystyrene foam?

Any thoughts on this much appreciated.

Thanks in advance....

 

[Newboy]

It may seem a daft question but how do you plan to heat the space once you have insulated it?

 

[kingofthehill]

I have already tried two electric convection heaters (2000kW each) and two fan heaters (also 2000kW) running simultaneously but this only just got up to 6 degrees c (I measured the temp). Will stick with the heaters i already have (one or all) for now. Want to avoid gas heating to minimise water vapour. Will consider alternative electric options if required.

 

[bolo 2]

I have considered assembling the panels with sealant to trap air internally in the panels

Looking at double glazed windows, I've got to ask myself, why is the space between the panes either filled with an inert gas such as argon or is a vacuum, if simply trapping the air would do the job?

 

[bernardgreen]

why is the space between the panes either filled with an inert gas such as argon or is a vacuum

stationary air is a good insulation but in double glazing units the air would mot be stationary ! The air in contact with the warm side would become warm than the air in contact with the cold side and thus convection currents would be created and the warmed air would move to be in contact with the cold glass and thus heat would be taken from the warm side to the cold side.

The "inert" gases are gases that have lower values of specific heat and thus they carry less heat from warm side to cold side ( The specific heat is the amount of heat energy per unit mass required to raise the temperature by one degree Celsius )

 

[JohnD]

in double glazing units the air would mot be stationary !

It is in sealed units because they are too narrow for convection currents to circulate.

I used to know the cavity depth needed for convection, but have forgotten it. It can happen in wider secondary glazing cavities.

 

[bolo 2]

stationary air is a good insulation but in double glazing units the air would mot be stationary ! The air in contact with the warm side would become warm than the air in contact with the cold side and thus convection currents would be created and the warmed air would move to be in contact with the cold glass and thus heat would be taken from the warm side to the cold side.

The "inert" gases are gases that have lower values of specific heat and thus they carry less heat from warm side to cold side ( The specific heat is the amount of heat energy per unit mass required to raise the temperature by one degree Celsius )

Thanks for clarifying!

 

[bolo 2]

It is in sealed units because they are too narrow for convection currents to circulate.

I used to know the cavity depth needed for convection, but have forgotten it. It can happen in wider secondary glazing cavities.

Your reply led me to visit here:
http://new-learn.info/packages/clea..._fabric/elements/cavities_and_air_spaces.html
I just love learning new things!

 

[bernardgreen]

In wide gaps there is a single and efficient convection loop from top to bottom. With narrow gaps there tends to be many shorter and turbulant convection loops.

With a single loop ther can a noticable difference in termperature between the bottom ( cooler ) and top ( warmer ) of the inner pane. This can be seen as indicating the double glazing is not working well. With mutiple loops the temperature difference between top and bottom is less noticable and thus ( salesmen claim ) thin gap is better.

 

[kingofthehill]

Well I came to my conclusion on the subject after reading this http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html which states that thermal conductivity of atmospheric air is better than polystyrene but also states that a vacuum has a thermal conductivity of 0W/(m k). I originally went through the list to see if any of the items with poor thermal conductivity values could be salvaged from household waste, such as polystyrene.

Also, on double glazing I read this http://www.gcsescience.com/pen16-double-glazing.htm and some other more in depth info on the subject which got me thinking about the sealed panel idea.

 

[kingofthehill]

So it sounds like there is mileage in my 'sealed' paneling idea? I could make the internal gaps smaller by spanning the cavity with cross battens. Also, from the link that Motivated1 posted, I realised that I could probably also benefit from lining the panels with aluminium foil to reflect some radiated heat from the door.

 

[bolo 2]

My neighbour, although by no means an expert on the the intricacies of double glazing, (his words, not mine), earns his living fitting double glazing windows. He tells me that he had to overcome a similar problem to kings when he tried to set up on his own many years ago. His solution was to install a totally sealed inner shell of plasterboard with some kind of wool filling behind the walls and a 200mm layer of loft insulation above the 'new' ceiling. The clever bit, again his words, not mine, was to install a secondary 'double glazed' door in the form of a roller blind of clear polythene. The edges of this new door were channeled into cable trunking. As far as he knows, the setup is still in use.

 

[kingofthehill]

Interesting concept, I find myself wondering how to seal the gap between the sheets though?

I think I will try and find out what the correct calculations are for this sort of thing and try and confirm for certain whether the sealed gaps in the panels will be of benefit, I should also be able to calculate the polythene idea then as well (must admit that the polythene solution would be quickest, cheapest and easiest so I think it's worth looking at).

Thanks all for your comments.