Monday, November 24, 2008

6.Can the washer machine benefit from the Miljødusj?

The Miljødusj is designed to heat the incoming cold water based on the drain water leaving the shower at the same time. It must be simultaneous to work efficient. I was first thinking of hooking up the washing machine together with the shower, but I was told it would not do much good. The washing machine does not drain anything until it is done with the washing cycle, and then the next water that flows inn would be for rinsing, which I believe is usually just cold water. But then I thought, what if I connect just the water inlet to the washing machine from the preheated outlet of the Miljødusj heat exchanger, and forget about the drain water going through it. Then I could start the washing machine right after my shower and harvest the left over energy. (Or possibly run it at the same time as I shower?) After my morning shower, I set the shower mixer to just cold water, and emptied 2 liter at the time while measuring the temperature. It gave be this table, that shows the energy value of the "leftovers" when I am done showering. I am not sure how much water our washing machine needs, but I would say it should be less than 8 liters. If so, it should be possible to squeeze out 85 Wh by also connecting the washer machine to the Miljødusj. Many ifs, and not a big potential saving. Based on this I decided not to connect our washer machine, at least not for now.


Rolf Nilsen said...

While playing the "what if game".. What if you had one central heat exchanger for greywater in front of your water heater and insulated PEX tubing for the greywater. Then you could have a washing machine feed from the waterheater, and reclaim 10-15 percent or more of the energy lost.

Svein* said...

The recover part sounds in part ok. But, if I understand you correctly, connecting the hot water to the washer machine might be too much of a waste. I belive that the first intake of water is for heating and washing the clothes, the next couple of cycles is rinsing. I have been told that rinsing is usually done with cold water. Supplying hot water instead will be a waste. The needed simultaneousness for heat exchangers is also questionable in this set up. It might be "almost" simultanious. I thought I have had is to make some sort of buffer tank for the grey water from the washer mashine with a valvue and a differential temperature control. If the water from the washer mashine is warmer than the water in the tank, then refil the tank. If the water is cooler, then dump it in the drain. The use of the tank water? Just for heating the room.

Rolf Nilsen said...

I have been assured that there are washing machines with one hot water and one cold water inlet. With such a machine, it could make sense to run a heat exchanger (or a combined heat exchanger for all greywater) to pre-heat water going to the water heater.

If you look at solar water heating systems, it is common to have a tank with a capacity of 750 to a 1000 liter in one household. A heat exchanger in front of such a tank sounds like a good idea. As always it is much easier to implement these things when designing a new house..

Robin the Energy Saver said...

My brother installed a drain heat exchanger a few years back. His connection makes a lot of sense:
- Water from either of the upstairs showers drains down a 10cm / 4 inch copper drainpipe
- The drainpipe has a coil of 1/2 inch pipe running around the outside
- The drainpipe is insulated outside the 3/8 inch coil
- The water supply to the electric hot water heater passes through the 3/8 inch coil pipe
- Water tends to run down the outside of a vertical drainpipe. When someone has a shower, hot water flows down the drain while cold water is simultaneously drawn through the outside of the drainpipe where it is prewarmed before entering the hot water heater.

Before the pipe was insulated and boxed in, my brother measured the temperature gain of the water flowing through the outside pipe towards the hot water heater, while someone was showering. The temperature gain is about 15C.

Unfortunately this set-up won't work very well for draining hot water that isn't simultaneously being drawn from the hot water heater. But at least the stationary water in the hot water intake gets warmed up, and when someone does turn on the hot water, that warmed water is drawn into the tank, saving some energy.

Robin from Green Energy Efficient Homes