Cheap efficient overnight cooling
 

I'm sure this has been done before but maybe will inspire others..

Our summer days can get very hot in Spain but the nights are much cooler. Leaving the Windows open to let cool air in works to a degree but there seems to be little air movement at night so the cooling isn't great.

I'm not a fan of air conditioning so although we have it in the bedroom I've rarely used it and the few times I have it has just been to cool the bedroom before going to bed, I've not left the machine running overnight.

So to capitalise on the lovely cool air I decided to build a window fan system using cheap table top fans. I found some 30cm fans that were very cheap on ebay and then simply cut a piece of foam board to the size of the open window and mounted 4 fans in it. The fans are mounted so they blow from inside to outside, pulling cool air in through any open window. As we have window blinds I can just lower the blind if I don't need to use the fans.

It works extremely well, can be easily regulated (plug in as many fans as I need), and does a great job of pulling in cool air.

Acuario

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Very nice setup!

I do a similar thing where I use a box fan in my upstairs windows. I usually stuff a pillow next to it to get it to seal up better. I like your solution better though.

A very strict cycle of heavy night time venting with whole house fan and closing up during he day last summer in my very air tight well insulated cabin kept temps well cooler than outside(as comfortable as AC) all day but lead to some heavy mildewing of leather items and some fabrics in storage areas where humidity condensed and air flow was stagnated. So natural night cooling can be overdone. Could use dehumidifier but that is a power demand I would not like to add. May have had more humid period last summer then normal. But I think that I was night cooling to near dew point inside during the day to much.

I really like this, too. Very elegant solution to a problem that many people are faced with.

I've thought to see if there could be improvement to an already good solution... only things I could come up with would be:

1. Use computer fans for greater energy efficiency

2. Use an acoustically 'dead' mounting board like Medium Density Fiberboard

3. If you really wanted to go over the top, you could hack a temperature controlled PWM speed controller.

Good work Acuario!

By the way, were you ever able to make significant progress on the Inverter Mini-Split compressor controller? Your work went farther than any I know of.

Best,

-AC_Hacker

I think building humidity control into the fan controller would be a great idea. I love the idea of cooling the house off with fans, but like Drake, it can get REALLY humid here. I think some sort of dew point calculating controller would be really awesome.

Originally, would you believe 10 years ago, when I knew I was moving to Spain I bought a whole load of computer psu cooling fans and made up a 6x6 grid of them to achieve roughly what I have now.

It did work but it was incredibly noisy and needed a separate psu to run the fans + wiring and mounting them wasn't easy as there was little space on them for mounting. I eventually abandoned them but the idea has always been there.

The fans now are mounted on a high density foam panel, the type they use for double glazing and the noise when all four fans are running isn't anywhere close to the old psu fans. The fans also have 3 speed settings so could be varied if necessary but for the moment I'm running them at full speed.

I did think about adding a controller to switch the fans on/off etc. but I wanted to keep it as simple as possible and quite honestly I think it would be somewhat overkill to add much control. Possibly adding a simple 24hr timer to switch them on/off is the most that is needed.

AC - sadly not yet - lack of time! Between the beginning of November and middle of February we demolished the old part of our house and built a new 140m2 (1500 sq ft for the imperial guys!) house for my parents. It is mega insulated (sprayed on expanding polyurethane foam 5cm in all the cavities, 7cm in the roof, 5cm in the floors, solar reflective glass in all the double glazed windows) and has under floor heating/cooling (using a home made air/water heat pump) which works impressively well. - Maybe I should start a thread as it is an on-going project with RS485 wall thermostats feeding back to a central controller to open/close the under floor heating valves, mixed heat pump/solar panel/ last resort oil boiler for heating..the list goes on.

I also invested time (as a necessity) into obtaining my certification for handling refrigerant gasses (it is a European requirement). Without this certificate I could no longer buy refrigerant gasses.

I still have the machine in my workshop and will get back to it at some point.

We'd love to hear about your parent's house build! Sounds great.

Absolutely!!

Bring it on.

-AC

I use the air conditioning if the dew point will be above 55 degrees F otherwise areas this would be an issue for me. Luckily we've had enough nights with dew points under 55 degrees F to where I've only had the house above 76 degrees in the hottest parts three days total so far. We've been lucky with a few 50-55 degree lows at night with dew points under 50 to where this has worked well. Usually this time of year that is out of the question. I find using the dew point forecast that comes with the weather.gov hourly charts to be especially useful and surprisingly accurate for temperature and dew point estimations. Oddly enough they seem to be the most accurate source of rain/snow forecasts that I've been able to find too, granted it isn't perfect because no weather forecast will be but it seems as close as it gets. It seems we are on our final week or two until cooling with windows open is not possible without high dew points and I will resort to air conditioning. ..haven't used it yet though which is the first year since I moved into this place 5 years ago in 2010 where I've been able to stretch it to mid-June without AC to keep the house low in moisture and cool here in Minnesota. It's been a great summer so far, mostly because of the rain keeping the clouds overhead. Not the best for the solar system though, I'm probably 100kwh short for the past 30 days and about the same for the 30 days before that.

My whole house(cabin) cooling fan is temp controlled(which I overrode last summer to see how cool I could get it). I will use it this summer and try to better match avg dew points. Iwas getting indoor morning temps into the 50's before closing up for the day. Cabin is very tight and insulated/shaded so interior temp stayed very cool well into late day. Which was very welcome as I was working hard outside during the heat of the day underpinning new foundation for new addition. I was pushing the cool beyond normal comfort.