Is it sensible to connect a washing machine/dishwasher to hot water?

Hello everyone,

somehow I just came across the topic in the title.

The following consideration. If I work with a ground source heat pump in a new building that has, say, an annual performance factor of 4-5, then it would make total sense to connect the washing machine and the dishwasher to the hot water line, right? This would provide a larger flow, fewer problems regarding legionella, and one could go to a temperature of 45-48°C, which benefits the efficiency of the heat pump.

The only catch I see: if I want to wash wool at 30°C or cold, I have to switch the connection. But that only happens 2-3 times a year for us.

And the additional hot water preparation would have to be taken into account when sizing the heat pump.

My thought is that you could actually save quite a bit of energy this way, since most of the energy for dishwasher/washing machine is needed to heat the water. Or am I wrong here?

I would appreciate your opinion.

Best regards Specki

First of all, your washing machine must have a hot water connection and be able to handle it. This is the case with very few machines. Normally, however, you do not save anything with it because the machines regulate their own production well. In addition, it is the hot water preparation that lowers the COP with heat pumps.

because most of the energy in a dishwasher/washing machine is used to heat the water. Or am I wrong here?

Well, since you only need to wash your laundry (except towels) at 30 degrees anyway, you can do without it for the washing machine. Does it have a hot water connection? This also applies to the dishwasher, which uses between 6 and 12 liters of water.

Morning

That is not a problem at all and also makes sense. The annual performance factor of the washing machine would be 1. The heat pump’s cannot be that bad. You don’t have to rewire anything, as there are pre-control devices available for standard washing machines. We have been using these for about 20 years. Google "Alfa Mix"

Olli

First of all, your washing machine must have a hot water connection and be able to handle it.
This is the case with very few machines.

Why does it need that? You can just connect the hot water to the normal inlet. Then 45° warm water comes in, and the machine doesn’t have to heat it because it’s already warm. I assume it has a temperature sensor and doesn’t just heat based on time.

Normally, you don’t save anything with that because the machines regulate their heating themselves quite well.

Yes, it regulates the heating well, but it needs about 4 times as much energy to heat the water compared to the heat pump.

Besides, it’s the hot water preparation that lowers the COP of the heat pump.

Yes, one would have to see what the heat pump’s value is when heating water to 45°. But it will still be significantly more efficient than direct heating with electricity.

Well, since you only need to wash your laundry (except towels) at 30 degrees anyway, you can skip that for the washing machine. Does it even have a hot water connection?

We usually wash at 40°. But even at 30°, the water would still have to be heated from about 12° to 30°.

This also applies to the dishwasher, which uses between 6 and 12 liters of water.

That would, however, be an argument against it.
Both machines work with little water. And probably not only is the water heated at the beginning, but it is also reheated several times during the process. So the effect would be smaller again.


Well, I don’t want to buy a €260 part for each machine now. Is it worth it?
I roughly estimated the saving at about €50 to €70 per year earlier. Then the part would have to “survive” 4-5 years for me to recover the costs.

Look here:

https://www.hausbau-forum.de/threads/spuelmaschine-an-den-warmwasseranschluss-anschliessen-sinnvoll.31159/

and here

https://www.hausbau-forum.de/threads/solarertrag-ist-nicht-ablesbar.27724/