Winter heating for a tunnel

[Small pumpkin]

How can I heat my 10"x 10" tunnel in winter without out it costing an arm & a leg?
I was thinking something along the lines of sola power collect in summer use in winter. But I know the battery's that are used are very expensive, so that's probably a no starter. Have considered double skin and insulation of some sort, but don't know how to do that and still have enough light getting in.
Things I have to consider 1, exposed site with VERY high winds regularly. 2,in winter very low light levels due to geographic location. 3, Lack of money so has to be something very cheep to set up and run.

There you have it mission impossible, if you except this mission this post will self destruct in 10 seconds

[Kristen]

Insulation is the cheapest for of heating A hedge / fence around the greenhouse, to keep the wind off (but not block light, natch!) will also make a big difference.

Electricity is probably your cheapest for just Frost Free - but you need a quality/accurate thermostat which will cost £50 although that will pay back in a year or two. Electric fan heater will only come on when thermostat needs it, so will run for relatively short period of time. Fan will move the warm all to all parts of the structure, and moving the air will help reduce moulds (worth running the fan-only in mild winter weather to reduce moulds, I have mine on a 15 minute segment timer 15-on and 45-off)

Getting electricity to a greenhouse tends to be expensive and obviously a non starter for the allotment

Bottle Gas heater would be next choice. It has a crude thermostat, so not on all the time, but it will over / under heat the greenhouse as a result of being only a crude thermostat. Over-heat = money wasted, under heat = dead plants.

Last on my list would be paraffin. Have to light that on nights when you think it will be cold, and its output is constant - so much the most wasteful, fuel-wide.

Gas and paraffin both produce moisture, so increase humidity, so you tend to have to vent to remove that - which kinda defeats the object.

Inter-seasonal storage of energy is difficult / expensive. A massive store of water in the greenhouse can help, and Dick Strawbridge built an underground heat-store using broken glass, and then blowing hot air through it in the day and the cold air through it at night to heat it. Dunno how effective it would be in practice, you'd still need a fan/electricity but that shouldn't need much power - car battery should be enough.

Trouble is that in Winter the solar insolation is only 10% of what it is in Summer, so there really isn't enough to actually heat anything sufficiently to overcome the cold, and any short-term store won't be any good if we have, say, a week of sub-zero temperatures and not much sun (although cold snaps usually come with high pressure / clear skies, so there is the chance of sun during the day at the same time)

[Kristen]

Sorry, forgot to post the link to Dick Strawbridge's broken glass heat store:
Solar Greenhouse Heat Sink - Solar

[veggiechicken]

Section off part of your polytunnel for your chickens to roost in overnight. Their bodyheat will heat the PT

[Kristen]

Section off part of your polytunnel for your chickens to roost in overnight. Their bodyheat will heat the PT

Does it help to pluck the chickens first, so they radiate more heat?

... I'll get my coat

[veggiechicken]

You'll be suggesting spit roasting next Kristen

[Small pumpkin]

Thanks for the info. I do like spit roast chicken
But as ever I have not made my self clear I need it heated to around 70c not just frost free. Another hair brain idea that is going to fall flat on its face

[roitelet]

Maintaining 70 in a poly tunnel is going to cost an arm and a leg no matter what sort of heating you use. I screen off the end of the tunnel with bubble wrap and use blow always in side then a gas heater from the beginning if March until the middle to end of May. I only have it set to come on when the temperature drops to 5c and I use a bottle of gas in that time. At 27 euros a bottle I think that is quite enough!

It would also be expensive to heat a glass house over winter to the temperature you want.

[veggiechicken]

70c What on earth are you growing that needs that sort of heat
Unless you're a millionaire, forget it

[Alison]

I was wondering what you wanted to do it there too? Assume you meant 70F otherwise you'd be in danger of melting your plastic. Even so, that's pretty hot and you'd be better off emigrating to somewhere hotter. I'd not dream of heating my tunnel but do keep my greenhouse frost free some years but means of insulation and a basic electric heater.

[Kristen]

70c What on earth are you growing that needs that sort of heat

That would be a Hot Water plant I expect ... must be 70F I think which would be 20C-ish. Still a tall order to heat to in winter IMHO

Glass would be better than Poly for that sort of temperature, and a conservatory / lean-to attached to the house even better (that's unlikely to go below 0C anyway, so less heating effort required, and adjacent to the house you can run an extension off the house central heating system which will the most cost effective heat source / fuel.

My "plant room" is south facing, insulated to better-than-building-regs, has radiators off the house central heating system, double glazed windows, and as such is well enough insulated that it takes little effort to heat it. When the sun pokes through the clouds in Winter it heats up nicely, the structure is made using high-density blocks, so absorbs a lot of heat during the day which is radiated out at night.

Trying to achieve that with a poly-tunnel as a starting point is going to be very hard indeed, particularly as far North as you are ... although I expect you have mild weather with the Gulf Stream effect?

Looking at Met Office temperatures I think you'd need to be living in SW or NW corner to have the benefit of the Gulf Stream

Met Office: Regional mapped climate averages

[Alison]

That would be a Hot Water plant I expect ... must be 70F I think which would be 20C-ish. Still a tall order to heat to in winter

Now I think about it, we don't heat our house to that temperature and our heating bills are still pretty high in a well insulated property.

[Kristen]

... in a well insulated property.

WAY off topic, but there is "well insulated" and there are solutions like "passive house" which has a level of insulation, and air tightness, that needs virtually no heat in UK winters (something like 1kW for a 3 bed house when the outside temperature is -10C). Sadly UK building Regs are nowhere near that standard

[Alison]

WAY off topic, but there is "well insulated" and there are solutions like "passive house" which has a level of insulation, and air tightness, that needs virtually no heat in UK winters (something like 1kW for a 3 bed house when the outside temperature is -10C). Sadly UK building Regs are nowhere near that standard

True, a friend of mine is trying to do that to her house at the moment, it's not easy to do as a retrofit but probably more feasible with new build if you have the foresight.

[teakdesk]

70F will mean plants are well into their growing phase when they also need lots of light.

Unless Isle of Mull has changed since I was last there the plants will grow very, very leggy and very, very weak. Probably be dead by end of winter.

You could use an intelligent controller that measured light levels and only raised the temperature to 70F when light levels high.

Keep temperatures more like 50F when light levels poor.