Just what is the point of bubblewrap?

Hi all, I've bubble-wrapped the greenhouse again this year. I hate the stuff as it lowers the light level a lot, is awkward to seal and is expensive.
However I got to thinking, if the reason why double glazing works is the fact that air is trapped in the gap between two panes of glass, why do we need the bubbles?
I have decided that next year I am going to use polytunnel PVC as an inside layer instead. As it is available in very wide widths, I can get a single piece to line almost the whole of the greenhouse, with separate pieces for the gable ends & sealed with tape. I could still probably use spacers and turn-buttons to fix it.
Polytunnel PVC comes in different grades, is generally UV stabilised, lets in optimum light, is easy to clean and will last for a good few years.
Is this a good idea or am I missing something?

 

the bubbles provide an extra layer of insulation, but I agree that that is probably negated by the gaps between the bits!

Has anyone tried using that shrink plastic & double sided sticky tape style style double glazing on a greenhouse? It was always very effective for the house windows, and lets the light through well. Maybe the dampness would stop the tape working though? I might give it a go on the conservatory next year, as the bibble wrap was a bit of a 'mare to put up.

 

I remember using clingfilm many years ago in a flat with single glazing, it worked fine.
The tape I use at the moment in the greenhouse works even if it gets wet, so it should be fine in a conservatory.
I am now even considering whether to leave the PVC in place all year round. I have to use shading in summer as the sun gets too strong, so why not let the PVC filter it a bit?

 

A single layer of poly would be at least as good if you can find a good way to fit it and as you say, lets in more light than the 2 layers in bubblewrap.

Still air is the actual insulator in most products,(loft,cavity wall,granular etc)
Most fibreglass insulation is 90% air, the fibreglass content simply stops it from moving about.

Heat (like air) will always take the easiest route so even a few small gaps could negate all the added insulation value.

Aside from air movement, the greatest losses come from radiant heat.. but still air insulation won`t prevent that

 

Hi Folks

I left my bubblewrap on the greenhouse for about four years and it worked very well indeed acting as both an insulator and shading. It was held in place with these ingenious plastic clips that are meant for the purpose. Only if you have a metal greenhouse that is.

All went well until a year ago when I was having trouble lighting my butane weed wand I think it is called so I took it into the greenhouse for shelter to light the match. Unfortunately my aim wasn't too good and I managed to set the bubblewrap on fire --- well a mixture of flaming and melting.

The fumes were so obnoxiuos I assumed they were highly toxic so I made a very hasty exit. I could do nothing but wait until it all died down and the fumes cleared.

So far I haven't got round to replacing it. I have just moved the frost tender plants into the conservatory.

Platty

 

Sounds horrendous, Platty.
Fire and poisonous fumes would make short work of any greenhouse weeds :D

When you replace it, keep the weed wand away from the greenhouse or have a hosepipe handy

 

Platty that sounds awful, lucky you have a metal greenhouse! :eek:
Hex, one of the reasons I thought that the PVC would work better is that it comes in wide widths - a 5m x 6m piece would cover both long sides and the roof of my greenhouse, plus the 2 further gable sections to seal with tape. Bubblewrap is about 1.2m - 1.5m wide so needs a lot of sealing tape to make it airtight.
If I had a second greenhouse I would probably do a trial, temperature, light levels etc.

 

Hi Blackthorn

Wider sheets are better, less joints and potential airleaks.
1" thick polysterene sheet where light isn`t an issue will be about 5x as effective.
It can also be used on the cold northside of the greenhouse (incl roof) and around the riser wall below the staging if need be.

As a test for your poly versus bubblewrap you could make 2 identical coldframes (nothing special). Cover one with bubblewrap, one with double poly.
A min/max thermomoter in each could then track any temperature differences and satisfy your curiousity

 

This all sounds very sensible - think I'll do what you suggest, Hex - well worth a try. The loss of light is a real problem, since the light isn't all that great to start with on many days, why reduce it even more? :rolleyes:

 

Winter light is terrible compared to the excess in summer but the diffused radiation from clouds helps a lot in winter

At this location at the summer solstice (21st june) the sun reaches approx 60 degree altitude at midday and draws an arc 125 degrees each side of due south (250 degree arc, sunrise to sunset).

In comparison at the winter solstice (21 dec)it doesn`t get above 14 degrees at midday (very low angle) and only draws an arc of 40 degrees each side of due south (80 degree arc, sunrise to sunset).

Quite a big difference

 

Surely the advantage of bubble wrap is the still air inside the bubbles themselves. The air between the glass and the bubblewrap or poly sheets will not be static and will be in contact with cold glass. The air inside the bubbles will be warmed by the heater and heat will be retained longer because it is not moving and not coming into contact with the cold glass. Bubblewrap does obscure light and needs to be removed in summer to ensure adequate ventilation as well as adequate light. Gonna get awfully mucky and dim if you retain it year after year to double up as shading. How will you clean the glass?

 

Hi Hornbeam

The light issues are quite a problem

The bubblewrap by itself isn`t a good insulator but then neither is 12" thick polystyrene if the air can get around it.

The benefit of bubbles are that they are self contained still air pockets which prevent convection currents.

Double glazing used in most houses has a maximum gap of about 28mm between the glass to prevent the air inside the gap from being driven by the same convection currents..notice that no one makes really big gap double glazing.

If air can move, it starts working like a conveyor belt, transporting heat to the cold surfaces where it will magically disappear

I like the idea that the bubbles will store the heat.
Consider that air heats up quickly and cools down quickly.
The reason is that 1 btu will heat 55 cubic feet of air by 1 deg F so you`d need quite a lot of bubbles (1kw = 3413 btu)
If you filled the bubbles with water that would be much better as heat storage (62 btu per cubic foot per deg F)

How to clean the glass? I`ve no clue on that one

 

Yes - its all a compromise. If we were really ecologically minded we wouldn't grow pampered plants in heated greenhouses at all. Victorians got it right when they used fermenting horse manure and straw as a heating source. Still operational at Helligan and Audley End I believe

 

I agree entirely.
I do think we should explore alternative ways of making the best use of resources though instead of just throwing more at it

The victorians were quite resouceful.
I`ve never been in a cold stable.. especially one with deep litter (a devil of a job to muck out though)

As simple as a greenhouse appears to be, it is a very complex beast.

Not only are the "normal" problems of insulation and draughtproofing there, but also evaporative cooling effects due to the damp environment with ventilation airflow, and of course, good old condensation which can be heatloss by another name

Even the plants themselves produce heat indirectly and add to the puzzle.

I guess we`ll just have to do the best we can

 

I have thought of buying solar panels for various purposes round the garden, which used with a car battery could supplement electricity used. My brother in law promptly pointed out that the amount of energy used in the manufacture of batteries and panels might be a significant factor in the saving, even though it sounds appealing.
Perhaps I'll put the guinea pig hutch in the greenhouse, and add a mini-compost heap!
it's very hard to decide what is a true saving and what is not- bubble wrap also costs money and materials to produce and as I don't think it's bio-degradeable where does that fit into the equation?