Wednesday, 15 January 2014

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.