Save Heat at Washing Machines

[Enthalpy]

Washing machines squander electricity to heat water, dishwashers too. That much:

(0.4m)³ = 64kg water from +15°C to +40°C is 6.7MJ=1.9kWh, in two passes 3.7kWh. Heat losses during the process make it worse. At variable 0.3€/kWh it costs 1.1€, just once a week is 170€ in 3 years, ouch. To +90°C it's 30MJ, in two passes 11kWh and 3.3€. Every second week costs 260€ in 3 years. Blistering barnacles!

We can fill the machine completely, and when possible wash in a single pass less warm, to save electricity, washing powder and water. I've just bought 6 bed sheets which the saved electricity will pay in 3 years, better than a savings account. But what can technology do?

Coal, gas, heating oil, maybe solar heat, are much cheaper than electricity. My grandmother had a washing machine heated by gas. Allegedly not convenient enough, but to save 3€ I'd go to the cellar twice. An engineer doesn't earn money at that pace. Plus, gas heating can be automatic. Better: obtain warm water from the central heating, dilute for +40°C, post-heat with electricity if needed. Clean that water if necessary, or use a heat exchanger.

If washing in two passes, the first wastewater could heat the second pass. This needs water storage at ambient pressure for the wastewater, a heat exchanger, and controls, but no insulation. To save half of 400€ in 3 years, the added hardware looks cheap. It needs room and smart customers.

At a laundry, hotel, restaurant... machines run often. Heat from the (second) pass could serve for the next machine load. 0.3m³ water allowed to cool from +90°C to +85°C in 24h tolerates 73W leak, at a sphere it's 70mm foam. A second insulated tank could recycle the heat at +40°C to +60°C. Or just neglect the refinements.

A collective house could use a similar storage, both if few machines are shared by many users, or if one user's heat serves for the other. Some policy can share the costs better.

Can a lone washing machine do the same? Imagine it serves regularly every week, or accept imperfect savings from random use. 64kg water allowed to cool from +90°C to +70°C in a week tolerate 9W leak. At a sphere it's >180mm foam, not little. Vacuum insulation would do it better.

A solid like bricks or a polyolefine could store heat. This would avoid bacterial growth in the wastewater tank, but it adds costs. It could double as the heat exchanger.

The water supply pipe is often long in a house. Running the wastewater close to it, in the opposite direction, with a common heat insulation, would implement the function imperfectly but with the minimum footprint. If shared among many machines, the insulation is less critical.

Marc Schaefer, aka Enthalpy

[swansont]

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Moderator Note

Perhaps with ideas like this, you could get a blog, and post it there? This isn’t really posing a question or inviting discussion. 

 

[Externet]

Or,  wash clothes with cold water.

----> https://www.geappliances.com/ge/lifestyles/6-reasons-to-cold-water-wash.htm

----> https://www.bhg.com/homekeeping/laundry-linens/tips-checklists/cold-water-laundry/

----> https://www.apartmenttherapy.com/washing-clothes-in-cold-water-vs-hot-water-35648166

[Enthalpy]

On 6/6/2020 at 5:36 PM, Externet said:

Or,  wash clothes with cold water. [...]

Somehow, I have in mind that bed sheets must be washed quite hot. I try to fill the machine completely then, that's why I bought many bed sheets.

I suppose (but didn't check in detail) that washing powders still don't work properly in cold water. The ones I find at supermarkets demand 30°C or 40°C at least. A washing powder efficient at cold would be the proper solution.

Information from a producer of washing powder or from a manufacturer of washing machines would convince me. In the past, they wanted hot water. If this changed, they should tell it, as it would be hugely useful. Their opinion has more weight for me than a Press article that bears no consequence from random opinions.

==========

Hi Swansont, I firmly believe that the readers feel invited to discussion, even if I ask no explicit question, just because this is a forum.

[Externet]

Always had the same belief.  Being a forum,  exposing a thought/theory without questions would be acceptable. Perhaps this was before the invention of blogs ?😐

[Area54]

1 hour ago, Enthalpy said:

I suppose (but didn't check in detail) that washing powders still don't work properly in cold water. The ones I find at supermarkets demand 30°C or 40°C at least. A washing powder efficient at cold would be the proper solution.

This item on the strengths and weaknesses of different temperatures, from 20^o to 90^o , provides some relevant background to your OP.

Your focus seems to be more on economy than environmental impact. What is your justification for that?

Edited July 13, 2020 by Area54
Insert missing link

[Enthalpy]

14 hours ago, Area54 said:

This item on the strengths and weaknesses of different temperatures, from 20^o to 90^o , provides some relevant background to your OP.

Your focus seems to be more on economy than environmental impact. What is your justification for that?

Thanks! Information by a manufacturer, I tend to believe them more easily. And they tell "60°C for bed sheets", which will save me €€€ as compared with 90°C.

Environmental impact resembles economy, as reducing the electricity consumption improves both. Filling a machine, too. Money has the advantage of being easier to count.

[studiot]

This EU report may interest you.

It is 2010, but I don't think there is a more recent one.

https://ec.europa.eu/environment/ecolabel/documents/Laundry Detergents technical report.pdf