Wednesday, November 19, 2008

5.Mesuring the cold water temperature increase of Miljødusj

I used two digital thermometers to measure the in and out temperatures of the heat exchanger under the shower cabinet. Each thermometer was strapped with a rubber band to where the pressurized water is connected to the Miljødusj, one on connection 1 which is incoming cold water, and the other on connection 2 which is the preheated water going to the shower.

My initial test setup was performed by cooling it all down first. I let the cold water flow in the shower for 5 minutes, then I took a quick shower. The plot clearly shows how the temperature of the out pipe to the shower increases from 15 to 26 °C (59-80°F) . The lowest graph shows the temperature increase which is about 11 °C . (The increase after the 6 minute mark is after I stopped showering).

The day after I measured my own shower which is usually fast, followed by our oldest son, Simen, who takes longer showers. ( Yes, teenager..) Looking at the graph you can see that the temperature in the room, and then also of the initial water in the heat exchanger, is 22 °C. When I start to shower the red curve shows the temperature of the preheated cold water pipe going to the shower. It is increasing all the way along as we shower. The blue curve shows the temperature of the incoming cold water pipe. Looking at the second shower you can see that it bottoms out at 14 °C . After a shower it heats up due to the last drain water passing through the Miljødusj and also later from the room temperature. The lower curve is just the difference between the two upper ones, showing the temperature increase, which is really what we are looking for. The difference show 11 °C . But is this the real temperature increase of the water? No, it is the temperature increase measured on the outside of the connecting pipes. If you recall the pictures of the inside of the Miljødusj, the out pipe goes from the back of the box and above the drain water back to the pipe connection to the shower. I assume the pipe temperature here is close to the water temperature inside the pipe. Around 25 °C . The incoming cold water is out of the picture I managed to take, but it is most likely very close to all the parallel pipes and in contact with the drain water. To check for this I just measured the cold water coming out of the tap. It showed 11°C . So when I measure 14 °C outside the pipe, the inside water is really just 11 °C. I am confident that the real cold water temperature increase in our shower is close to 14 °C (57 °F) from 11 °C to 25 °C.
Continue reading here: 6.Can the washer machine benefit from the Miljødusj?

11 comments:

Rolf Nilsen said...

Interesting stuff. I think the miljødusj is way overpriced, but would like one or two myself for our home :)

Have you done any calculations on how much you stand to save annually and how long the payback time will be?

Svein* said...

Hi Rolf,

Yes, I am working on it. Currently we have two showers in our house, only one with the Miljødusj. Trying to get most of the family to use that one instead of the other one. The Miljødusj is about 7 kg, and the price of copper is stiff. I looked into making one myself, and were planning to use at least NOK 1500 just on copper pipes. I am measuring all the kWh that our water heater uses, so in some weeks I should have some figures that should be an indication on the savings.

Rolf Nilsen said...

I am looking forward to seeing your data. greywater heat exchangers will be important in the future as energy prices (and pollution) soars.

7kgs, of which perhaps 10% is soldering tin and plastic. Hmm, thin walled alu could also be tried. It is tempting to try and make a similar heat exchanger.

Vi kan forsåvidt skrive på norsk også, men siden bloggen og sidene er på engelsk så.. :)

Svein* said...

Comments in Norwegian or English is probably a good idea.

En varmeveksler er jo gankse enkle greier, så det går nok fint å lage en selv. Pass på at ikke den aluminiumen blir for tynn slik at den kan sprekke ved høyt trykk. Om jeg husker riktig så leder aluminium varme bare halvparten så godt som kobber, men koster til gjengjeld bare en seksdel.

Trond-Atle said...

Flott blogg!
Vurdere sterkt å kjøpe en slik varmeveklser selv. Hvordan er den å vedlikeholde? Regner med at såperester og fett kan avleire seg og redusere virkningsgraden uten vedlikehold/rengjøring?

Svein* said...

Jeg har også tenkt på dette. Det må nødvendigvis avleiere seg noe på kobberrørene med tiden. Imidlertid så renner nesten alt vannet ut av Miljødusjen hver gang den brukes, så den blir tørr. Burde ikke blir mer avleiring der enn på gulvet i dusjkabinettet. Jeg har tenkt å sjekke om et års tid hvordan det ser ut inni der. Eventuelt kan man forebygge med litt plumbo. Kanskje det kan ha en effekt å helle kokende vann (f.eks restvannet etter at du har kokt pasta)ned i dusj sluket en gang i blant for å løse opp litt. Hvis du passer på å ta din daglige dusj samtidig, så har det hvertfall den effekten at du får "turbo" varmet opp litt kaldtvann :-)

Anonymous said...

Hei Svein - Johan her, representant for Miljødusj.
Jeg har først nå lest din blogg med interesse og kan bekrefte dine målinger fra andre kunder. Sistemann ut var en servicetekniker fra et miljøfirma som målte 15 grader temperaturøkning og en varmegjenvinningsprosent på 42,3 eller noe lavere hensyntatt tid før full effekt. Han hadde imidlertid lavere inngangstemperatur på kaldvannet: Dette gikk fra 3 -> 18 grader. Det sier også produsenten: lavere inngangstemperatur gir høyere gjenvinning.
Hva du sparer blir så et enkelt regnestykke hvor tallene på vår hjemmeside byttes ut med tall du mener er representative for egen families dusjmønster og dusjhode (kan måles med en 10-liters bøtte).

Sipke Paulides said...

Hi,
I have read your blogg with high interest, after I have been looking for this solution for a long time.
I know a simular solution which costs 1500 Euro and you with that never earn again:
http://www.technea.nl/home/prod=44/
Its in Dutch, but you get an impression of the product.

So, I bought the miljødush.
My results are warming up from 4 to 18 °C (having quit cold water in winter).
This gives me app. 40% energy savings per shower (10 l/min, 5 minutes, shower temp 41 °C).
The real gain is less due to the warming-up time when starting the shower, and the leftover energy in the system after ending the shower.

I also measured 10 °C temperature drop in the drain water (35 °C in / 25 °C out).
I will do more measurements in summer.

I experienced that the drainwater inlett stopped the water inlett when using the flexible pipe. Water was heaping up in the shower, loosing its energy. So I changed that to a straight pipe, problem solved.

Second, I concluded that it is better to remove the "hair filter" in bottem of the shower cabin. It stops the drain water. When I remove the filter, the preheated coldwater increases with app 2 °C.

According the dutch supplier (URL above) the highest savings (60%) can be reached when connecting the preheated coldwater both to the shower and the warm water tank. The producer of miljødusj says it does not matter. I havent tried yet but wonder who is right on this.

Further I wonder if there is any difference in effect if the cold water connections would be shifted, so that the water direction is changed (its water under pressuer, so it is streaming anyway). Havn't tried that eather, but will try that later.

I hope to read more of your interesting blogs !
Sipke Paulides
Årdalstangen Norway

Svein* said...

Hi Sipke,

It is interesting to see that you get a similar increase for the cold water temperature in your Miljødusj. Looks like I got a bit higher temperatur increase than you, which might be related to a slower water flow in our shower. Slower water flow should give more time for heat transfer.

I think the flexipipes are the weakest part of the Miljødusj. It is intersting to see your 2 C increase in temperature just by removing the hair filter at the bottom of the shower. It clearly shows that it is important to get the drain water to the Miljødusj unit as fast as possible, before it looses heat to the surroundings. What sort of pipe did you use? Was it a rigid type? I would like to see a hose type of pipe. Bendable, but smooth inside.

The Miljødusj is only connected to the cold water inlet of the shower. Assuming that your shower use 50% preheated cold water, and 50% hot water, we can say that about half as much cold water is flowing in the Miljødusj as drain water. However, if we also connected the hotwater tank to the Miljødusj, we will have just as much water flowing in both directions. Using the simple fact that the most heat transfer occures with the highest temperature differences, it is to me obvious that connecting the water heater as well will increase how much energy you can recover. Picture how twice the cold water flow will make the pipes colder, and then the drain water leaving the Miljødusj will also be colder. Colder drain water means more energy recovered. I would say the Dutch supplier got this one right.

The most heat transfer occurs in a counter-flow arrangement. Wikipedi explains this well: http://en.wikipedia.org/wiki/Countercurrent_exchange#Overview . Looking at the picture in my blog http://urge4lessenergy.blogspot.com/2008/11/looking-inside-heat-exchanger.html The cold water is flowing into the picture while the drain water will be flowing out of the picture. This is not exactly a perfect counter-flow, but the general direction seems to be optimal as recommended by the Miljødusj standard connections.

Svein*

Anonymous said...

Hi, I am interesting in this one. Can you tell me how the experience is by using this? If one have a shower that does not measure the temperature of outgoing watter, I guess one will experience hotter shower after a few minutes. Is this experienced by you?

Svein* said...

We have a thermostatic mixer in our shower. I have to wait the needed time for the hot water to reach the shower from our water heater tank, and then the temperature will be as I have set it, usually 38 C. Now, if you have a manual hot and cold mixer, you are probably used to playing with it for a while untill you get the desired shower temperature. The heat exchanger works almost instantaneously so I would think your adjustment prosedure would be very close to what you are used to.