Ventilation Vs Aircon Efficacy/efficiency

[samran]

So, we've signed a lease on a four storey townhouse in BKK. All levels are obviously connected by a starwell. No doors between each of the levels and the stairwells, though the bedrooms have their own doors. But the kitchen and lounge/home office levels (1st and 2nd floor) are totally open plan.

At the top of the stairwell is a small window/vent which the previous resident kept shut from what I can tell.

I'm thinking on the basis that hot air rises, it is probably best to keep the small window open at all times to help expel hot air. But given this is Thailand, where humidity is an issue, is opening the vent being counterproductive from an aircon usage perspective. Or, will there be enough outward ciculation through that vent to let the hot air out, but no humidity in?

Any thoughts would be welcome.

[brimacthai]

When ever you exhaust air out it has to be replaced with air from somewhere else... like the outside air. If the incoming air is hot and humid and is not treated in some fashion such as with air conditioning or an energy recovery ventilator then yes... you will be bringing hot humid air back into the space.

I have the same setup in m y place. 3 floors with access to the flat roof. I have a ventilator (some call it a whirly-gig) or something like that. Most of the time the outside air is at least cooler than the air inside and hot air does rise. So for the most part in the unconditioned common area, I get some free cooling effect and a nice flow of air through the house.

Hope this helps... if you need more info just PM... this is my field of work!

[jackflash]

Yes, if Air goes out, new (hot) air must come in.

With modern house design the secret to efficient ventilation is to use a "transverse flow heat exchanger"

The heat exchanger passes incoming air past the outgoing air (via a metal barrier) so no heat (or cold) is lost.

The house is carefully built so it is air-tight. All external walls have a plastc barrier and all joints are taped closed.

The builders actually test the house by blowing air in and measuring the pressure rise.

Another name for it is "Active Insulation".

Aparently it's an old idea in nature. Some ducks have a heat exchanger in their legs to prevent heat loss due to blood circulating through their feet in cold water. Likewise some fish separate their blood flow through inner and outer systems to prevent them freezing.

Facinating stuff, but sadly not much value for the renter however.

Edited May 31, 2013 by jackflash

[TommyDee]

a/c itself is a heat exchanger as a/c doesnt cool air, it removes the heat from it. that vent might be quite handy if you installed an extractor fan and flaps on it as all this talk of sealing a home may be efficient but it also breeds tale air. I open all the windows here inthe morning and run a huge extractor fan for a while to suck out the old air and draw in fresh air, create a breeze and remove smells from cooking etc.

the revolving cowels on a roof are good to allow the space in the roof to cool beofre it works its way into the house.Depending on the direction your home faces, insulated curtains are good to keep the heat out from the sun at certain times too. we have vertical blinds with blackout on the outside to reflect it and tinted glass.

but sealing a home is illegal in the Uk as it is unhealthy apart froma anything else, so look to ways to freshen your air and keep cool

all the best

t

[MaxYakov]

Yes, as other posters said, any escaping air will have to be replaced with other (outside) air. Hopefully, the replacement air is slightly cooler than the escaping air - the case with, let's say, an attic fan.

My experience and concern in Thailand has been focused on air cleanliness, not humidity ... except in the case where I attempted to cool my room with an evaporative cooler for a short period. It raised the humidity excessively, so I use it nowadays as a filter/fan after fitting it with an intake air filter and running it without the cooling water. It was one of my worst purchases in Bangkok, albeit second-hand, which with a little ingenuity turned out to be one of my best. Unlike a blade fan, it was easily converted to be an air filter and easily installed to intake air through the bug screen of an open window. I even bought a HEPA air filter for it for super-cleaning the air within the room If I so desire.

When I lived in Sukumvit near soi 4 on the 3rd floor and fairly close to an expressway the high carbon content of the air became apparent with my blade fan accumulating soot and a film of black grim accumulating in the room. I attempted to cool the room with outside air at night and found that the air had to be filtered because of its inherent pollution. Eventually, I fabricated more elaborate filters to place a positive pressure on the room at all times so that filtered air would keep out polluted, outside air even when doors were open. This worked fairly well in reducing carbon pollution within the room.

When I moved to Din Daeng on the 6th floor, but still fairly close to a major thoroughfare (Pracha Songkhro), both heat and pollution became factors. Heat, because the room had three, southward-facing windows and a westward-facing balcony door. Pollution, because my fan/filter was blackening a 3M filtrete^TM filter in 20-30 hours of operation. I applied many square meters of aluminized poly ceiling insulation for the windows and balcony/bathroom doors to handle the heat and have evolved into an essentially closed room with 24/7 aircon when I'm in the room. My electricity is around 2500 THB/month @6 THB/KWH, but would be much more if I didn't economize elsewhere such as 99% LED lighting, power-saving TV mode (thank you, Sony), etc.

I rarely bring in outside air for cooling these days because I've acclimated to 27-28 degrees C and the outside air is only rarely that cool. I have installed the 3M aircon filters in the room evaporator, however to assist in cleaning the room air of carbon and dust (which has been noticeably reduced in the room with this regime).

Also, my refrigerator has always been placed outside on the balcony both to make best use of the floor space and to remove it as a source of heat within the room. Since my balcony in Din Daeng gets direct sun a good deal of the day, I've had to place a layer of aluminized poly ceiling insulation on its top and sunward side.

If you are lucky in Bangkok, humidity would be a greater concern than the (it seems to me) pervasive air pollution. If you're running a blade fan, check how rapidly it accumulates the black soot of Bankok air pollution. Or install aircon room evaporator filters (I found by experimentation that the 3M filtrete were the most effective) and see how quickly they get dirty.

Edited June 1, 2013 by MaxYakov

[bbradsby]

OP quote: "I'm thinking on the basis that hot air rises, it is probably best to keep the small window open at all times to help expel hot air. But given this is Thailand, where humidity is an issue, is opening the vent being counterproductive from an aircon usage perspective. Or, will there be enough outward circulation through that vent to let the hot air out, but no humidity in?"

The aircon will be working harder if you keep the vent open, as hotter outside air will be pulled in through the door & window gaps to replace the air that leaves through the vent. My recommended low-tech strategy for thermal comfort in concrete buildings (which I assume yours is) in hot, humid Aw Climate zones is to keep the house closed up tight as long as the outside air temperature is higher than that inside; weatherstrip all openings; keep the sun's radiation from heating up the concrete masses via shading and/or radiant-reflective paint; keep all glass shaded or apply spectrally-selective film; ventilate the attic well; and insulate the top floor ceiling assembly to 150-200mm thickness. Then increase air movement in occupied spaces and/or dehumidify the air (aircon set on 'dry') to your personal comfort zone.

[indyuk]

When ever you exhaust air out it has to be replaced with air from somewhere else... like the outside air. If the incoming air is hot and humid and is not treated in some fashion such as with air conditioning or an energy recovery ventilator then yes... you will be bringing hot humid air back into the space.

I have the same setup in m y place. 3 floors with access to the flat roof. I have a ventilator (some call it a whirly-gig) or something like that. Most of the time the outside air is at least cooler than the air inside and hot air does rise. So for the most part in the unconditioned common area, I get some free cooling effect and a nice flow of air through the house.

Hope this helps... if you need more info just PM... this is my field of work!

If the house is air conditioned to the point that the temperature in the house is lower than the external ambient temperature humid air will not enter the house via a high level vent unless encouraged mechanically or a ground floor vent or door is open.

[MaxYakov]

OP quote: "I'm thinking on the basis that hot air rises, it is probably best to keep the small window open at all times to help expel hot air. But given this is Thailand, where humidity is an issue, is opening the vent being counterproductive from an aircon usage perspective. Or, will there be enough outward circulation through that vent to let the hot air out, but no humidity in?"

The aircon will be working harder if you keep the vent open, as hotter outside air will be pulled in through the door & window gaps to replace the air that leaves through the vent. My recommended low-tech strategy for thermal comfort in concrete buildings (which I assume yours is) in hot, humid Aw Climate zones is to keep the house closed up tight as long as the outside air temperature is higher than that inside; weatherstrip all openings; keep the sun's radiation from heating up the concrete masses via shading and/or radiant-reflective paint; keep all glass shaded or apply spectrally-selective film; ventilate the attic well; and insulate the top floor ceiling assembly to 150-200mm thickness. Then increase air movement in occupied spaces and/or dehumidify the air (aircon set on 'dry') to your personal comfort zone.

Good advice, IMHO, and I've used most of these approaches to both reduce heat incursion into my living spaces which are air-conditioned most of the time. The only thing that I can say is that better and more flexible than the window film is the use of aluminized (or mylarized) 5mm or 10mm, .6m x .6m polyethylene foam (ceiling) insulation. It is also available in large rolls. At Home-Pro - I paid only 399 THB for a 4-meter roll wide enough for a door. The advantage is that it can insulate in a very general way and that, in the case of windows, is not permanent and easily cut to window-size and easily removed as necessary.

Additionally, it is helpful if one becomes familiar with reading the KWH meter and able to determine instantaneous watt consumption by timing the KWH meter wheel. Also, isolating or eliminating heat sources from within the room such as converting to LED lamps/bulbs and placing the refrigerator on the balcony or a non-air-conditioned space. See my previous post.

Door and window seals also assist in reducing insect incursion. I've fabricated door seals using double-sided tape and polyethylene foam for my main entry door to keep out ants that had a nest in my neighbor's apartment. Anyone has ever had a cockroach infestation will know what I mean ... but my roach (actually, insect) war is another story ....

Edited June 1, 2013 by MaxYakov

[bbradsby]

When ever you exhaust air out it has to be replaced with air from somewhere else... like the outside air. If the incoming air is hot and humid and is not treated in some fashion such as with air conditioning or an energy recovery ventilator then yes... you will be bringing hot humid air back into the space.

I have the same setup in m y place. 3 floors with access to the flat roof. I have a ventilator (some call it a whirly-gig) or something like that. Most of the time the outside air is at least cooler than the air inside and hot air does rise. So for the most part in the unconditioned common area, I get some free cooling effect and a nice flow of air through the house.

Hope this helps... if you need more info just PM... this is my field of work!

If the house is air conditioned to the point that the temperature in the house is lower than the external ambient temperature humid air will not enter the house via a high level vent unless encouraged mechanically or a ground floor vent or door is open.

theoretically true. however, all doors & windows leak air even if weatherstripped, and all of the common building materials & assemblies allow air to pass through. So much, that in a light breeze, the entire home's inside air volume can be displaced in an hour's time. So the open vent above the stairs will, in combination with these leaks, accelerate the convection current that pulls in hot outside air.

[samran]

Guys, thanks for the fantastic information so far. Am learning a lot. Weatherstripping and insulation seems to be a common theme. Does anyone have a good idea as to whether these products are readily available in Thailand? I'm guessing home pro will have something, but it will be expensive?

In therms of orientation and building material, the place is built of brick, and most of the windows are west facing. The townhouses of course are semi detatched, we are middle one with one on each side, so we arent exposed to any direct sunlight apart from the west. The ground floor is fully covered (actually it is a covered car park) and the first floor which covers the car park has trees gardens and a pool. The lounge faces west onto this garden area, and so do all the bedrooms. As such, our lounge is quite well shaded with foliage, so I am guessing the ambient air from the bottom two floors will be cooler, if only a bit.

We are also well away from any main roads, down a very quiet soi, so dust and pollution shouldn't be as bad as other places we've lived.

[MaxYakov]

Guys, thanks for the fantastic information so far. Am learning a lot. Weatherstripping and insulation seems to be a common theme. Does anyone have a good idea as to whether these products are readily available in Thailand? I'm guessing home pro will have something, but it will be expensive?

In therms of orientation and building material, the place is built of brick, and most of the windows are west facing. The townhouses of course are semi detatched, we are middle one with one on each side, so we arent exposed to any direct sunlight apart from the west. The ground floor is fully covered (actually it is a covered car park) and the first floor which covers the car park has trees gardens and a pool. The lounge faces west onto this garden area, and so do all the bedrooms. As such, our lounge is quite well shaded with foliage, so I am guessing the ambient air from the bottom two floors will be cooler, if only a bit.

We are also well away from any main roads, down a very quiet soi, so dust and pollution shouldn't be as bad as other places we've lived.

I used Home-Pro (Rachada) for my insulation purchases and found the 5mm and 10mm aluminized or mylarized polyethylene foam sheets and rolls fairly reasonable (for Home-Pro, that is). It could be that not all stores carry it. The Rachada store is fairly large.

I used scrap pieces of the PE foam for weather-stripping fabrication because of the large gaps between door and frame (warped door). In the past, I've purchased ready-made weather stripping from Home-Pro, including door-bottom, brush-type seals.

You are very fortunate to be in a low-dust/pollution area. Makes one breathe easier. Good Luck!

Edited June 1, 2013 by MaxYakov

[brimacthai]

If you're planning to air condition the house and require fresh air intake then a energy recovery ventilator should be considered. This recovers the cool energy from the air before it is exhausted out and pre-cools the fresh air coming in. Here's a link (not to my site) about energy recovery ventilators: http://www.airchange.com.au/products-projects/products/ventilators/erv-ic-70/

In almost every case the temperature is not the problem, what we do is to use an air conditioner to provide dehumidification more than cooling. The problem with this is an effect called "over-cooling" which adds considerable amount of money to the running cost.

Another issue in moisture removal using standard air conditioning is having a "wet" cooling cool. Most people think that the water coming from the condensation drain is good... in actual fact a cooling coil that is wet can be more than 30% less efficient than a dry coil.

If you can keep your room/home at say 27C and 45% RH this will have the same feeling to us humans as 22C and 60% RH. But the cost of cooling the air from 27 to 22 is a huge portion of your air conditioning cost.

And of course the reduction in humidity means the air conditioner will be much more energy efficient. So what's the answer?

Here in Thailand it is a bit difficult to use modern off the shelf products but there are a couple of things you can do to get the most from your system.

The first step is to have a high quality air conditioner. This is one industry you get what you pay for and you will always pay. Meaning you buy a cheap A/C unit and it will cost a fortune to run, or you can pay extra when you buy one and get a very efficient system

The second thing to do is to buy a small portable dehumidifier. Again in choosing one the rules for buying A/C's applies.

The third thing you can do is install a wast heat recovery system on your split air conditioning unit that will produce all of your hot water for showers, laundry and dishes.

The nice thing is in most cases if you're only renting, you can take these with you when you move.

Here is a picture of what a waste heat recovery unit looks like.... with storage you have all the hot water you need for free, if you're running your A/C.