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BaseApe

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Hi all,

I'm new to this site and have had a look around but can't find anything directly related to my question so I'll just throw it out there and see if anybody can give me some guidance.

I recently built myself a greenhouse out of an old bird cage.  Here's a pic: [packhams-triumph-pear-april-2015-225x300]   

At the moment, I don't have any ventilation in the greenhouse and the midday temperature reaches 55C (on a sunny day) despite the fact that we are approaching the winter solstice here in the southern hemisphere.  So, before installing vents, I've been considering a way to effectively attach the greenhouse to my house so that I can get some free winter heating into the bargain.

Given the siting of the house and yard, there are two plausible locations for the greenhouse and both are in the front yard. One would be right next to my front window.  This would be a very easy option to implement. I envisage simply opening the window to allow the air from the greenhouse to enter the house.  However, it would no doubt make the facade of the house look a little strange to have a greenhouse sitting there.

Option two is more aesthetically pleasing. It involves placing the greenhouse near to the side of the house in the front yard.  However, I'm wondering how I should go about transferring the heat in this scenario.  

I can place the greenhouse right next the house which means the distance the air will have to travel will be small.  Here's a brief idea:  [schematic%20for%20air%20transfer] 
I would prefer a passive setup if possible but I'm happy to think about fans to help this work.  

What do people think?  Could a simple air transfer be effective in this case?  How much would the 90 degree angle affect air flow?  Is passive viable in this case?

Any thoughts would be most appreciated.

gbwillson

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Reply with quote  #2 
Hi BaseApe, and welcome!

Which way is towards the sun in the drawing? Where are you located?

If you are bringing air into the house via the greenhouse, you will also likely need air exchanged from the house to enter the greenhouse. This exchange of air can really make a difference in heating costs as the coldest air from the house is replaced by the warmest. You can also consider using fresh, outside air as your supply air, although this would likely be an issue for the plants. The problem I see with using greenhouse air to enter the house is the possibility of not only humid, possibly moldy air to enter the house. You may also have some chemicals such as fertilizer and pesticides entering the house. 

My suggestion would be to at the very least make the heated air entering the house isolated from the greenhouse air. One way you could do that is with a tube, downspout, or can type heater. This would warm the air inside the tubes, but not expose you to potential issues of warm, but bad air. 

I do think your greenhouse has a lot of potential for adding heat to your house. It's just a matter of getting it into the house in an effective, safe manner. But I'm sure we as a group can figure something out. I've never seen a problem that this group can't solve.

Greg in MN[wave]


Garage_Hermit

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Reply with quote  #3 
Hiya, Base Ape, welcome aboard !

Here's a few pictures of attached greenhouses.

And here is one bloke's sad experience...

Why not just build a low-inertia sunspace instead, and leave the GH where it is ...

OR build an attached greenhouse by all means, but separate the two with a Trombe Wall.

G_H

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BaseApe

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Reply with quote  #4 
Hi Greg and G_H,

Thanks a lot for the replies. You've already highlighted one thing I hadn't thought about i.e. moisture.

I'm in Melbourne, Australia which is at 37 degrees latitude. We have a "Mediterranean" climate here. Long, dry summers and cool, moist winters. We don't get snow here and, as I am close to the ocean, we don't even get frosts. On the coldest morning of the year it might get down to 3C. Usual winter overnight lows are about 7 or 8C and daytime lows about 13 or 14C.

My house points more or less due north which means lots of winter sunshine (southern hemisphere remember [smile].  In that schematic I drew, north is at the top.

I didn't originally intend for the greenhouse to be attached to the house so I am more than happy to leave it where it is.  However, it seems a waste to vent out all that heat.  My main goal for the greenhouse is to start seedlings which will then go out into the garden and also to tinker around with a few little experiments eg. trying to grow tomatoes in winter.

I am surprised that you say that the air quality from the greenhouse would be bad. I had always thought one of the benefits of an attached greenhouse was improved air quality as the plants in the greenhouse would be releasing oxygen while the humans in the house are releasing carbon dioxide.  But it sounds like that's not the case?

I'm happy to do the work to eg. put a trombe wall in or otherwise separate the air. But it would be good to know in advance what sort of heat gain I can expect so I know whether it would be worth it or not. From my research, I've seen that heat gain is a function not just of heat generation but also air flow, which is why I was concerned with how much air I could get to move.  

Given the surface area of the greenhouse facing the sun is about 8m2 (86 ft2), is there any way to calculate expected heat gain given a certain air flow?

Thanks,
Simon
SolarInterested

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Reply with quote  #5 
Quote:
Originally Posted by BaseApe
... I didn't originally intend for the greenhouse to be attached to the house so I am more than happy to leave it where it is.  However, it seems a waste to vent out all that heat.


Further down the page GH linked to is a section about Storing Greenhouse Heat (link). Depending on how complicated a build you want a heat ex-changer in the green house could transfer hot water to your house for heating. Given your climate you probably won't have worries about freezing of the small diameter piping between the greenhouse and your house.

A storage tank in the house or greenhouse would allow you to save daytime heat for use at night.

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Both temperature rise and airflow are integral to comparing hot air collectors
BaseApe

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Reply with quote  #6 
Thanks again, G_H.

I think I can now see my confusion.  I was imagining the greenhouse as like a standalone version of the Low Thermal Mass Sunspace that you linked to earlier.  So, I was thinking the challenge would simply be how to move the air from that sunspace (greenhouse) into the house.

Basically, I was hoping for an easy bit of free heat [smile]

But it already sounds like it might be more trouble than it's worth.  I've been planning to have a go at building a couple of Solar Hot Air Collectors for some time (in fact, that's how I originally came across this forum). So, I think I should probably tackle that first and hold fire on the greenhouse.  In any case, the greenhouse is ideally located at present. It faces due north and gets full sun all day long.


Garage_Hermit

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Reply with quote  #7 
sounds like a wise plan !

G_H

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gbwillson

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Reply with quote  #8 
In any case you still have a nice place to hang out in the winter months during the day. On nice days I would sit in the greenhouse and read or take a nap. If you do grow veggies during the winter, make sure you keep plants away from the side panels if possible. I also put a sheet of insulation along the north wall to better protect the plants and allow you to place them close to the wall. Another trick I used was to set the plant trays on an old electric blanket. On the coldest nights I would turn on the blanket and it would help keep the roots warm and create a micro climate surrounding your most sensitive plants. 

Greg in MN
stmbtwle

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Reply with quote  #9 
There are a couple greenhouse heat-exchanger setups here and in Build It Solar, how about one of those with a second fan coil in the house? Water lines are a lot easier to bury than air ducts, and you leave the humidity behind.
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Willie, Tampa Bay
SolarInterested

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Reply with quote  #10 
I had similar thoughts up-thread Willie. It would almost make the greenhouse an ARETHA type collector.
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Both temperature rise and airflow are integral to comparing hot air collectors
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