First Test of the Greenhouse

[GoggleboxUK]

I panelled out yesterday and moved everything inside that I want to overwinter and today I set up internal and external thermostats on the Temple/Greenhouse.

At the moment it's 5.4c on the outside and 18.7 on the inside

That's only a 1 degree drop since 3pm this afternoon so the heatsink is obviously working nicely.

I know I won't get a proper idea of how well it will work until I get some subzero temps but this is very encouraging.

[Yorkshire Kris]

I panelled out yesterday and moved everything inside that I want to overwinter and today I set up internal and external thermostats on the Temple/Greenhouse.

At the moment it's 5.4c on the outside and 18.7 on the inside

That's only a 1 degree drop since 3pm this afternoon so the heatsink is obviously working nicely.

I know I won't get a proper idea of how well it will work until I get some subzero temps but this is very encouraging.

Thats a very encouraging start to your temps. It's 4.9 outside and 13.3 inside my greenhouse (but I have the fan heater running set at that temp)

[redsquirrel]

I panelled out yesterday and moved everything inside that I want to overwinter and today I set up internal and external thermostats on the Temple/Greenhouse.

At the moment it's 5.4c on the outside and 18.7 on the inside

That's only a 1 degree drop since 3pm this afternoon so the heatsink is obviously working nicely.

I know I won't get a proper idea of how well it will work until I get some subzero temps but this is very encouraging.

sounds very promising.are you recording the temps overnight?
if not,might be worth popping out a few times just to get an idea a bit later on

[stephenprudence]

My greenhouse generally settled to the same temperature as outside, there is no heat sink, I have to heat mine, but until I get some wicks, that wont be possible!

[GoggleboxUK]

Thanks guys

Yes Darren, I will be recording temps so I will get lows from both tomorrow morning.

Not had the heater on at all, just had the fans sucking warm air down below ground for a few hours this afternoon when it was reading 25c in there.

I'm hoping to keep it at 5c minimum and use the heaters as little as possible. The extra expense in the build should be saved within a few years if I don't need to use the eleccy very often.

[GoggleboxUK]

I've just checked again at 23:10 and its 4.3 outside and 18.9 inside.

[Tom2006]

Sounds perfect in there!!

[flounder]

Be interesting to see how much it drops by morning, but I think you've done good there

[GoggleboxUK]

I'll post the results of the overnight low but it's curremtly 3.7 outside and 19.0 inside.

I imagine that as the ground temperature cools and the days get shorter there will be a smaller gap between the two but, in all fairness, I did do a good deal of research and tried to figure out the best ways to avoid losing heat and keeping the running costs as low as possible.

I don't know if anyone watched Kevin McCloud build his shed but I found his methane production system very interesting. I may well have a go at something like that myself after this year as I have 2 dogs that would be great for powering a bio-waste recycling unit if the electric gets too pricy this year.

[Dave Brown]

Can you explain, as the temp is falling outside, why the temp is actually rising inside over many hours You seem to be gaining heat this evening that was not there in the afternoon, and I don't see how that is possible

At 15:00 this afternoon my lunar module was 21.6C with an outside temp of 11.4C, but at 02:00 this morning it is 12.4C with an outside temp of 4.6C. It has a brick wall to the garage, a double brick wall to the garden, a glass wall to my conservatory and a 10mm twin wall poly carbonate to the Washingtonia, with a shingle floor, and temp drops overnight, so I really don't understand how your temp is rising with no sunlight and falling ambient. Where is is gaining this extra energy from that wasn't there during the day

[GoggleboxUK]

It was there this afternoon.

The air pumps pull the heat down below ground into a gravel heatsink Dave. I had the pumps on for about 2.25 hours this afternoon and the recorded temperature at that time was 25c so, basically, I am pulling 25c air down into the gaps between the gravel 3 feet below the surface.

As the temperature in the greenhouse cools the heat below rises. If the temperature above is the same as the temperature stored below there is no thermal rise as the heat has nowhere to go. This is why I used 25mm multiwall polycarb and tried to make the greenhouse as well insulated as I could above ground using lots of heat retentive stone. Even the benches inside are cast stone so as to act like storage heaters and the corners are 18" thick stone in the place where traditional greenhouses lose most heat. If the heat is lost at a fast rate, as it is in normal glasshouses, then the 25c air below is consumed and lost quicker. Without a heatsink the volume of air to be cooled is considerably less and therefore faster cooling due to contact with cold surfaces like the glass.

As the air in my greenhouse cools it is heated from below with air fro the heatsink and the temperature remains, hopefully, stable. As long as I can refill the heatsink each day using air warmed by the sun then I won't need to heat the air artificially.

Of course this is all theoretical in my greenhouse at the moment because it needs lower temps and shorter/duller days to see how efficient the method really is but the system is being used in the US and Canada in industrial scale greenhouses to grow food crops all year round.

I have noticed very slight drops in temperature (0.2 degrees) tend to only last a short time before they stabilise again. The stable temperature looks to be around 19c as it hasn't been more than half a degree either side of that temperature since the sun went down.

Currently it's 2.9c outside and 19.0c inside.

[JonK]

All very interesting Google. I'm planning a new greenhouse for the new garden and was thinking about putting in a heat sink to help maintain night temps. Do you have any links to your design or similar designs?

By the way, my other half comes from Kirkham. Her parents still live there.

[Dave Brown]

I'll have to look into this for the house, as well as the Lunar Module

[Kristen]

I'll have to look into this for the house, as well as the Lunar Module

There was a house on Grand Designs that had a Mechanical Heat Recovery Ventilation system (I expect you are familiar with it, if not its just a forced air ventilation / extraction system with heat exchanger between Incoming and Exhaust air to reclaim the heat).

Anyways, the Grand Designs house buried a 4" diameter, or maybe larger, standard orange underground drainage pipe along the length of their drive (and then up a brick pillar at the entrance) as the source of the incoming air. Idea was the ground temperature would cool in Summer and pre-heat in Winter.

[GoggleboxUK]

Well temperature inside the greenhouse did eventually start to fall and the max/min inside the greenhouse read a high of 27.2 and a low of 8.9 so I assume that the heat sink eventually ran out of 'fuel'.

As Kristen says, ground source heating is a good method and the heatsink will benefit from the surrounding ground temps so I am hoping that won't ever fall below the 5c mark in winter and have a cooling effect in summer (although that's not important as I remove the panels).

I'm not really looking forward to colder weather or shorter days but I should be able to draw more conclusions once the conditions deteriorate, Over all things look promising at the moment.