Cooling a sun room with A/C and windows

[DaveC426913]

I've got this 300 square foot sunroom off the back of my house. It was hastily and amateurishly assembled by the previous owner. It's got a clear, corrugated panel roof, and large windows on the south and west walls. There are lowered panels that block much of the roof light (which probably just means it's creating a little greenhouse there above the panels).

I keep the wndows open and a good cross breeze stops it from turning into an oven. But it's still just a bit too hot for comfort. I bought a portable air conditioner (14,000 BTU) to see if I can bring the temp down to a more tolerable level.

Here is my question: since I'm sure the vast majority of heat is due to insolation, it seems to me that - even while having this portable A/C on - I should keep the windows open. Otherwise, the heat coming in will just stay trapped. It's only about 25C outside.

Is my logic messed up? Would it be better to close all the windows and let the A/C do its work?

Full disclosure: I know this is a Sisyphean project. I'm trying to keep a sunroom cool that's mostly windows, and what isn't windows is poorly-built walls that leak air like a sieve. It'll surely kill my electrical bill - but what else am I gonna do?

 

[Flyboy]

I’m on the road until tomorrow night so I don’t have the reference book that I would love to use, but I think I remember enough about it to be helpful…

If you put some vents up above those lowered panels and allow the air to flow into that space, it should set up a nice draft all on its own to help vent the room. One of those wax actuator driven vents would probably be a great choice for controlling the vent, but a manual system would work too. That should help pull the worst of the heat out.

I would also run the air being pulled into the room through the air conditioner to maximize the effectiveness of the AC. If nothing else, it’ll serve as a dehumidifier for the incoming air.

 

[russ_watters]

Dave, it looks like you're overthinking. It's very simple: if the temperature inside is cooler than outside (whether AC is on or not), the windows should be closed. If the temperature inside even with AC on is warmer than outside, you need shade too, or a big fan and open windows instead. There is no circumstance where you should have the windows open with AC on.

 

[jack action]

If the temperature inside even with AC on is warmer than outside, you need shade too, or a big fan and open windows instead.

There is no circumstance where you should have the windows open with AC on.

Seems contradictory.

But I'm with you with the shades. Never underestimate the power of a curtain.

 

[Baluncore]

Seems contradictory.

I do not understand that statement.
Please explain your reasoning.

 

[jack action]

I do not understand that statement.
Please explain your reasoning.

If with the AC on you need open windows [and a big fan; or shade instead], then there is at least one circumstance where you could have the windows open with AC on.

That is how I read it.

 

[russ_watters]

If with the AC on you need open windows [and a big fan; or shade instead], then there is at least one circumstance where you could have the windows open with AC on.

That is how I read it.

No, I mean if your AC can't lower the indoor temperature much below ambient you should turn it off and open the windows/use fans instead. And if your envelope load is that bad, you should try to fix that, whether you try again with AC or just keep the windows open.

 

[Rive]

...you need shade too...

Greenhouses (agriculture), 'sunrooms' and such are usually for spring and autumn (well, they are good at winter too, but they just burn money. Lot and fast ).
At summer, it's pretty common to have some shade cloth installed.
Well, it's already common to have that outside too

 

[DaveC426913]

If you put some vents up above those lowered panels and allow the air to flow into that space, it should set up a nice draft all on its own to help vent the room. One of those wax actuator driven vents would probably be a great choice for controlling the vent, but a manual system would work too. That should help pull the worst of the heat out.

Thanks, I will put that on my list.

I would also run the air being pulled into the room through the air conditioner to maximize the effectiveness of the AC. If nothing else, it’ll serve as a dehumidifier for the incoming air.

Well, my choices are windows or A/C. ASo I guess I close the qindows and pull the air in via A/C.

Dave, it looks like you're overthinking. It's very simple: if the temperature inside is cooler than outside (whether AC is on or not), the windows should be closed. If the temperature inside even with AC on is warmer than outside, you need shade too, or a big fan and open windows instead. There is no circumstance where you should have the windows open with AC on.

OK. Windows closed. Got it.

At summer, it's pretty common to have some shade cloth installed.

Now that you mention it, I'm not so much interested in a direct sun room as a shade room. I like the bright outdoor light, but no direct sun for me. (I go to Cuba twice a year and spend the whole time in the shade.)

These shades, they go inside? i.e. hang them under the transparent corrugated panels? I'll make them loose-weave enough to let some % of light in. I guess white is better to reflect. Maybe linen or gauze.

Thus?

 

[Rive]

These shades, they go inside?

With a highly reflective material it might mean some help, but in general if it is dealing with the radiation inside then the associated heat will remain inside (the greenhouse).

 

[Flyboy]

Agreed with Rive, putting them inside is not ideal. I would put it on the outside with at least a few centimeters of standoff if practical.

 

[DaveC426913]

Agreed with Rive, putting them inside is not ideal. I would put it on the outside with at least a few centimeters of standoff if practical.

Sure but how would that work? I can't put curtains above the roof.

 

[jack action]

Sure but how would that work? I can't put curtains above the roof.

They make everything:

​

https://www.youtube.com/results?search_query=house+roof+retractable+awning

 

[Flyboy]

Sure but how would that work? I can't put curtains above the roof.

Can you post a photo of the area in question? I might have some ideas.

 

[DaveC426913]

Looking North:

That slope is certainly not to-code. It's about 1:12.

(Don't judge me. We're still moving in.)

 

[sophiecentaur]

you need shade too,

Of course. Prevention is always better than cure (and cheaper). There are many designs of blinds with highly reflective top surfaces; not too expensive and easy to install. Edit: The 'greenhouse effect' will be minimal if you reflect most ashort wavelengths back out of the roof glass and the blind absorbs very little IR.

AC is too often used as a first line of thermal control when passive methods are available. We have an energy crisis at the moment.

 

[DaveC426913]

There are many designs of blinds with highly reflective top surfaces; not too expensive and easy to install.

You can see the styro roof panels are silver reflective. At least, they are on the underside; I dont know if they are reflective on the top side, or whether the PO installed them upside down.

But I don't want them opaque or it defeats the purpose of a sunroom.

 

[DaveC426913]

What material can I use that will give me overhead light? I realize this is an oxymoron - wanting to let light in but not wanting the heat.

If I had my druthers, I would use some sort of cloth, like linen, but of course that won't be reflective.

 

[Tom.G]

There is something called "Low E", for "low emisstivty", glass.
IIRC, it is rather pricey.

A semi-informative post at:
https://physics.stackexchange.com/q...lass-that-is-impassible-to-infrared-radiation

(Image from: https://i.sstatic.net/55BAy.jpg)

Cheers,
Tom

 

[sophiecentaur]

What material can I use that will give me overhead light? I realize this is an oxymoron - wanting to let light in but not wanting the heat.

I have so called Magic Glass on my conservatory roof and walls. (This a different house than the last one with blinds.) It lets visible light in but blocks IR. The energy in the narrow visible range is very little compared with all the rest. In sunlight, the conservatory doesn't get intolerably hot but, in winter, the 'contained' heat keeps the inside warmer than outside. This is in the south of UK so we seldom get excessive temperatures (that is until things started to go silly recently)
I found this ad. Others are available and I don't know the name of my supplier but you get the idea.