Ventilation Leak

Sam had an interesting issue with the mysterious appearance of water at his house in November. A narrow stream started appearing down a wall at the back of his house. Luckily it was on the outside. 

It came from the same place on the wall and seemed to be there all the time, although he could not confirm whether it was there while it was raining!

This seemed condensation-related, and evidently the cause was a problem with the seal on the exhaust vent meaning that instead of going outside, the exhaust air was going under the outer skin of the house. 

By November, it is usually colder outside than inside. The air is being cooled by the heat exchanger in the ventilation system as it leaves the house, and with at least a 10 degree temperature difference, and up to 50% relative humidity inside, this means the humidity of the exhaust air will usually reach 100% by the time it leaves. Since the ventilator does not have 100% efficiency, the exhaust air will always be a little warmer than the outside air, and have some moisture to deposit as soon as it hits something.

The something that was hit by the saturated and slightly warmer air seems to have been the inside of the siding, and the water found its way outside, where it dripped merrily away.

Dripping Diary

26th January, 2016

Water started dripping from the ceiling in the pantry this morning. 

When you have water dripping out of somewhere, it's a good idea to find where it is coming from and stop it from going in there. 

The immediate suspect, like the last five times water has appeared in unwanted paces, was the ventilation system two floors above.

This is actually the second water incident in the last months, but the first one was quickly noticed from the sound of drips on the bathroom ceiling, so it never got to build up anywhere. 

There was no dripping on the bathroom roof this time. That's because it was not the ventilation system leaking, even though that's where the water was ultimately coming from.

I quickly came to a second hypothesis. Half a metre of snow outside... temperatures below freezing for a few days... the drain from the ventilation system coming out of the wall about twenty centimetres above the ground... frozen pipe! 

left: drain from ventilation system

The first evidence to support this hypothesis was the water spilling gently over the the top of the drain beneath the ventilation unit, rather than actually going down it. 

A bit of hosepipe with a loop usually goes from the ventilation system to the drain. I diverted it into a bowl to stop sending more water to the overflowing drain. 

The next evidence was outside: a large icicle coming out of the drain.

A few buckets of hot water and kettles later the icicle was gone. The visible part of the icicle went fairly quickly and was soon followed by the rod of ice from within the pipe. It took a little longer to thaw the elbow. Immediate problem solved, it was time to address the cause.

The ventilation system is going to produce condensate when it's cold outside, unless we also make it cold inside, or drop the relative humidity below about 20%. It's often going to be below freezing when it's cold outside, and that's where the water is going to be dripping. So it seems inevitable that ice is going to form and, sooner or later, the outlet pipe will freeze. It will then fill up with water and start overflowing. The only mysteries are: why has this not happened before? and why did the contractors not prevent this from happening?

I suspect this probably has happened before, but it takes a while for the pipe to fill up with water before it overflows, then it takes a while for the water to drip down, around the bath that is one level below the ventilation system, then onto the ceiling of the pantry below the bath. Some of this water will be evaporating all the time, and it could be a couple of days before enough builds up to break through the plaster boards and start dripping onto the floor. By this time, the temperature outside has always gone high enough above freezing, or a few rays of pre-noon sunshine have reached the drain and thawed it. 

I was wondering if there were any mitigating circumstances leading to this, and there are a couple of things that may have made a difference. I noticed when I was clearing away another icicle a couple of days later that I'd left a gardening stake directly underneath the drain, from which was growing a nice icy stalagmite. Perhaps such a stalagmite had helped to block the drain. I was in too much of a hurry to melt the ice before and didn't document the hydro-crystalline pathology very well. 

The other thing that we had done the night before this incident was to put on the humidifiers. It gets a bit dry in the winter since we're constantly getting rid of our humid air, and replacing it with air that's already fairly dry, and is then being heated so that the relatively humidity will fall about four times. We don't have any permanent remedy for this, but when we remember, and when it gets below about 30 percent, we switch on some of our humidifiers, usually at night time. So we are adding moisture to the warm air that we are expelling from the house over a steep temperature drop, and increasing the amount of water that will end up in condensate.  

According to my previous calculation, the amount of water that's going to drip on a cold night is up to around 450 ml per hour. One drop is 0.05 ml, so that would be about two and half drops per second. Not fast enough to represent constant flow, but perhaps slightly faster than the ideal drip rate for forming icicles, which seems to be around one or two grammes per minute according to the Icicle Atlas. The precise temperature and humidity of the air in the house will determine the dew point, which will likely be a few degrees above zero. The dew point is really the critical number since it will tell us when condensation starts. 

It's 23 degrees C and 30% humidity right now, so the dew point is 4 degrees. (According to this dew point calculator.) So if the air outside goes below about 2 degrees, it's going to drop below the dew point within the ventilation system. If we had 100% efficient heat exchange, then it would be cooling the air all the way down to 2 degrees, and the air coming in would be heated all the way up to 23 degrees. It's more like 80% so we lose a couple of degrees. Some ventilation systems will recover only 60% of the heat, so they will be less likely to reach the dew point. This is only a problem that will happen in well-ventilated houses with highly efficient heat exchange ventilation systems, so I suppose that answers the question of why the contractors hadn't thought about this happening, and why we've had so many problems with this. 

When I say we've had many problems, we haven't exactly been wading through water, just needed to use a small cloth to mop up a few drops from the floor every year or two. And hopefully the structure of the house has not been damaged by the moisture. 

The other problem ventilation systems have to deal with is freezing condensate. If the air is being cooled below freezing, it may start snowing in there as vapour in the air is precipitated. This would block the ventilation and we would no longer be able to ventilate the house, so the ventilation system does something with pressure differences to stop that. I'm not really sure what it does, but the result will probably be that it never gets as low as zero in there, and in fact there may only be a very narrow window of outside temperatures when condensate is actually being produced.

(Apologies to anyone who was hoping for a story about cooking fat from the North of England.)

Note:

The other drain in the picture is from the air conditioner, which we have hardly every used. This has a de-humidifer on it, and it would take moisture out of the hot air if we were using it. There is no chance of it freezing though. 

Read about previous escapades here.

Writing a nice letter

It's taken over a month to write to the supplier of heat but not a lot of light.

This is a translation of the first letter I wrote:

==
Dear @?x@*,

Thank you for your visit to our house to look at the third incident of leaking water from the ventilation system you installed. A couple of weeks later I went into the room where it lives, and found an overflowing bucket, which made me realise that the problem had not been fixed. I was shocked to hear that you expected me to pay for you to come again, so I got the manual and looked at it myself, following the clear and straightforward instructions on removing the cover, taking out and cleaning the heat exchange unit. Instructions that would be difficult to miss, unless you did not look at them.

While doing this, I noticed that the water was not draining properly from the pan in the bottom of the machine, even when the drain was clean and water was flowing smoothly through that. Water was collecting at the front of the machine, allowing crap to build up, as you can see in the enclosed photograph. Excuse my use of an engineering term.

Using a spirit level showed that the whole system is not level, and in fact the way it has been installed, hanging from the wall, it was really never likely to be level in the first place.

I'm not sure whether this is a design fault of the system, a flaw in the manufacturer's installation instructions, or if there is any other way of passing the responsibility on to someone else, but there are a couple of ideas you could use.

If you, or other companies, continue installing heat exchange ventilation systems in Japan, it would be nice if you could take problems like this seriously and ensure installation and maintenance that will not lead to leaking. Somewhat counter-intuitively, heat exchangers with better efficiency have bigger temperature drops so more condensation will come out of them. If it does not have a well made path, this water will make a new one, likely through the part of the house where it will do the most damage.

At the moment I'm thinking of the best way to make the system level.

In the mean time, please don't worry about our health. We will clean this regularly to avoid an outbreak of legionnaires disease.

Yours...

==

Of course, I didn't send this. Actually I didn't really write most of that until now, but that's what I wanted to say. I know that at most it would have caused still more heat, and not achieved any of my goals, except for some short-term satisfaction.

Obviously my main priority is to get my system working properly, although I think to do that I'll probably have to learn how it works and do the maintenance myself.

Another very big priority is stopping this happening to other people. These kinds of systems are essential to highly efficient buildings, and if they cannot be installed correctly people will stop using them.

So here's the second letter:

====
Dear @?x@* san,

Thank you for coming to look at our leaking ventilation system. Two weeks afterwards I realised that the system was still leaking, so I followed the manual to clean it, including the heat-exchange element. While doing this, I noticed that water was not draining properly from the bottom of the system because it was not level. You can see in the enclosed photo how dirt has built up at the front of the drainage area. Using a spirit level showed that the system itself is not horizontal.

If you have any suggestions as to how the system can be made level, please let me know.

I hope that you will be able to avoid this kind of problem in future installations of heat exchange ventilations systems.

Yours...

====

Stick to the facts. We need to stick to the facts.

Here's the final version of the letter:

======
Dear @?x@* sama,

Sorry for the delay in contacting you.

Thank you for coming to look at the water leakage from our heat-exchange ventilation system on 17th January. Two weeks later I realised that the leaking had not stop, so I cleaned inside the system and the heat-exchange element, as described in the manual.

At this time, it became clear that the system was not level, and water was not effectively draining from the system. Water was collecting at the front of the draining pan, leading to a build up of dirt, as can be seen in the photo.

Upon measurement, the system was not level, and was out by about 5 mm in 100.

I'm now thinking of a way to make it level.

Yours,

======

The morning after sending this, a reply came back:

==

Long time no see.
I looked at the attached photos.

I can't see whether it's level from the photos, but we will think about this.
==

How much water is in the air? A worked example

Here's a practical physics problem. I have a leaking ventilation system with a bowl catching the drips.  How often do I have to empty the bowl?

Assume it's 20 degrees inside, with 40% relative humidity, and a little below freezing outside. Assumptions are approximate. All the best ones are. Save the precision for what you know.

A cubic metre of saturated air hold a little under 20 ml of water at 20 degrees C. A little under 5 ml at freezing. The ventilation system is set to shift 150 cubic metres per hour, so that's something like 450 ml of water per hour. The bowl holds 2.9 litres. It's going to fill up in about 6 hours.

Oh no, better go and empty it!

Dry air and dripping pipes

It is the dry season once again, and we have two problems. The first is keeping the house humid, and the second is avoiding pools of water on the floor. 

A few days ago I was in the bath and heard a dripping noise. The drips were going in and out of sync, playing the kind of rhythm that will maintain the attention of someone relaxing in a nice warm tub. It sounded like there were two drips at different frequencies. Absorbing as this harmonic analysis was, my main concern was where the drips were coming from, and whether they were building up somewhere, planning a journey through wall and floor cavities to appear where they would do as much damage as possible. 

Opposite to the UK, Japan has high humidity in the summer and low humidity in the winter. Rather than those damp winter days of drizzle and sleet, we often get clear days when the sun is out and the sky is blue, but the temperature struggles to go above freezing. When air is cold it holds less moisture, and since the relative humidity halves with every 10 degree temperature rise, by the time this air gets into our house the relative humidity is probably in the teens. 

Most of the moisture in the air inside is then either residual moisture released from the walls and wooden floor, or moisture that we have added, either deliberately with our humidifier, or as a consequence of hanging up washing, cooking food, or breathing. I'm sure our house plants contribute something to the humidity too, if we remember to water them. 

When this air leaves the house, it goes through the heat exchanger in the ventilation system, and with the drop in temperature of around 20 degrees, the relative humidity quadruples. If we've succeeded in getting the humidity over 30%, into the comfort zone for people and wooden buildings, that quadrupling will put the relative humidity over 100% and water will precipitate inside the heat exchanger, hopefully getting into the drain and finding its way out of the house. 

This is where I thought the drip was coming from, but it sounded like it was coming from outside. I opened the window in the bathroom and it didn't sound like it was coming from outside after all. Next I went up to the room with the ventilation system, which is directly above the bathroom, and heard nothing and saw nothing there. At this point I gave up, hoping that it was something happening within the pipes. 

A couple of days later I listened a bit more carefully and traced the drips to the ceiling of the bathroom. I got a step ladder, and opened the inspection door in the ceiling, which was quite exciting as I'd never done that before. Then I could see the drips coming from the pipe draining the ventilation system above. When I went upstairs there was a small pool of water under the drain where it comes out of the machine, and it looks like the fitting is leaking. There is a bowl under it now, and at the end of the long weekend, we'll call the builders and see if they can come and fix it, again.  

Drip drip drip

I already mentioned pools of water and houses and the question not being if it will happen, but when. It seems a bit soon to get another one, and a little inconvenient that it was on a Sunday when I had to work.

When I was making breakfast I saw the small puddle and the drips coming from the ceiling in the utility room. The utility room is directly under the bathroom, so that's where any water is going to end up. Although it doesn't have much respect for a house free of fungi, water does at least obey the laws of gravity.

The first reaction was to call the plumber. Actually the first reaction was to get a bucket for the drips and a cloth for the puddle as it still hadn't got very far. Also, since it was dripping quite slowly, I thought we should let the plumber finish his breakfast.

I finished my work early enough that the plumber was still working, searching for the source of the leak. When I spoke to him on the phone, he hadn't found it, and was about to give up and go home. He said the water was not coming from the bath or any leaks in pipes there, but from the wall between the bath and the boiler.

Thinking about the mystery on my way home, like a Poirot of plumbing, it increasingly seemed that the ventilation system was the problem. In the process of exchanging heat, the ventilation system takes a lot of water out of the air, which must find its way through a drain out of the house. This seemed the most likely source of the water.

The night before had been the first below freezing, and I wondered whether the outside drain from the ventilation system had frozen over, stopping the water from escaping. Of course the temperature had only just dipped below freezing, so it wasn't cold enough for pipes to freeze, and there had not been enough time for a dam of water to build up and get through the ceiling.

When I got home, the first thing I did was look at the drain as it leaves the house on the East side. There was no ice there. In fact the drain pipe itself was dry.

The plumber showed my the pipes above the utility room when I got into the house, and the one that water was dripping down the outside of. We went upstairs to the boiler, which was installed by different tradesmen and was not really his responsibility. There were pipes coming in from the external heat exchange units for the boiler, and the air conditioner that we don't use. There were just two pipes for each: a supply and return for the coolant. No drains.

I then suggested the room upstairs, which he had had nothing to do with, and was unaware of. Above the bath is the machine room with the solar power conditioners and the ventilation system.
And there was the smoking gun. Or at least the dripping pipe, and a pool of water underneath the ventilation system.

The pipe coming out of the ventilation system had come out of the drain in the floor. It had not been fixed in there, but was just pushed in, the ventilation "experts" no doubt hoping for the best. I go into that room about once a month, and it could well have been knocked out when I was vacuuming the floor last time I was in there a month before. Water had been slowly dripping onto the floor, gradually increasing in flow as the outside temperature dropped. As it found its way down past the bath, following the pipe, it would gradually have evaporated back into the house. For the last couple of nights, as the temperature dropped to around zero and the amount of moisture coming out of the air in the house increased accordingly, more or the moisture got to the puddle above the ceiling of the utility room, and in the morning it finally got through the drywall. In fact the dry wall was now a wet ceiling.

It's a good thing we'd just used drywall for this room rather than a plastered and painted ceiling. A screw driver is enough to take a panel off, and it can easily be replaced without needing to call in a procession of tradesmen. The drywall panel is now propped against the wall to let the ceiling dry out, and I can put it back again in a couple of days without having to call the plumber out again.