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PostPosted: Sun Aug 29, 2010 2:56 pm
by andykidd
Hi all,
I am curious if you have any experience of energy and water efficient
I am buying a dishwasher to work with my own solar power and gravity
fed rain tanks. Bosch, LG and Fisher & Paykal all tell me they no
longer make any dishwashers with hot and cold inlets - because it made
their energy ratings worse!!??! However, a technician told me to plumb
the hot water into the only inlet, have it at a minimum of 65 degrees
Celsius, and that it needs water pressure of at least 35 kpa, which
equates to 3 meters of head when only gravity fed. So this may work,
but I am keen to hear of anyone else's experience around this.
For me to set the water temperature at 65 degrees may be illegal: I have solar hot water which may not be that hot, so the gas instant booster has a thermostat, but the legal maximum is 55 degrees. What to do?
All the best, Andy

Re: dishwashers

PostPosted: Sun Aug 29, 2010 6:53 pm
by relaxedcamper
I read your thread and can't offer any real world experience except. What came to my mind is the idea of the washer only having one cold water input and the washer heating this water to a set temperature. So rather than trying to supply 65c water to the unit, surely regular household hot water supplied to the washer would be then heated by the dishwasher to the operational temperature by the washer itself?

If this is the case then you just connect the hot tap on and use the sun to heat it as hot as it can and just use the dishwasher do the rest.

Re: dishwashers

PostPosted: Sun Aug 29, 2010 7:38 pm
by andykidd
Yes but -
I am avoiding using electrical power to heat the water inside the dishwasher as I only have solar power. Also, gas boosting hot water is more efficient than electrically heating water for anything.

Re: dishwashers

PostPosted: Mon Aug 30, 2010 3:19 pm
by 470rigby
relaxedcamper wrote:If this is the case then you just connect the hot tap on and use the sun to heat it as hot as it can and just use the dishwasher do the rest.

The inlet water valves on Dishwashers with single water connections are generally not designed to handle water temperatures over 60/65 degC (depending on make/model), so you can't do this. You could probably replace it with a high temperaure valve and hope that hoses and fittings handle the higher temps from your solar HWS.

Alternatively, you could fit a tempering valve on the inlet to keep the inlet water below the reccommended maximum for your appliance.

Re: dishwashers

PostPosted: Wed Sep 01, 2010 10:49 am
by Tracker
andykidd wrote:However, a technician told me to plumb the hot water into the only inlet,

From one who does know - connect to COLD water and let the DW do the heating.
The DW needs COLD water to wash correctly.

If you seek efficiency, then get a simple MECHANICAL (non computer) machine and a timer.
Mine is loaded and set in the usual way, and the time-clock (behind) turns it on at 5AM, such that it uses OFF PEAK power.

andykidd wrote:Bosch, LG and Fisher & Paykal

Don't touch Bosch.. LG is usually good for spare-parts prices, FingPaykel are fair but NOT the DishDraw.
Look for a SMEG or ASKO or some model with a NON-ELECTRONIC control.

Re: dishwashers

PostPosted: Wed Sep 01, 2010 12:45 pm
by sande
Tracker wrote:
The DW needs COLD water to wash correctly.

Why :?:

Re: dishwashers

PostPosted: Wed Sep 01, 2010 1:52 pm
by Tracker
WHY - COLD water..

Simple - We are dealing with food. Proteins like Egg and Cheese etc. will cook onto plates if hit with HOT water.
DishWashers are designed to fill with COLD water and rinse the proteins from plates etc.
The DW will then empty, re-fill with cold water and release the soap and start to slowly heat the water..
It is this process of slowly heating and the washing with soap that removes (supposedly) the remaining egg etc. from plates.

Would you not think that there is a practical reason why there is NOT ONE dishwasher on the market, that fills with hot water only and some do have Hot and Cold inlets and therefor use both Cold and Hot..?

If you hit the contents with HOT water, you will cook the gunk on and will then have to scrape it off.

On the economy side of things - A DW uses a tiny amount of water.
Most often - the water will fill and start to get hot just as the DW reaches full.
So in this case, you might still need to heat the water, despite having drained that much Hot water from the tank. So you waste the energy used to heat the tank water, and then use MORE to get it back to the right temperature..

We love our DW - It gets used about every second day.. Again - we are oblivious to it's operation.. The time clock switches it on at about 5am and at 7am we just open the door to allow passive drying..

Just repeating - there is NO DW in the world that is designed to fill with Hot Water - That is no coincidence..
AND - I admit that I did not understand these factors when I installed our DW (many years ago) and I connected it to HOT only.. I have since run a cold line and it does seem to work better.

Re: dishwashers

PostPosted: Wed Sep 01, 2010 4:33 pm
by wbdeejay
I must disagree with Tracker.

As far as I know all commercial kitchen dishwashers run with hot water. Whether they have a hot supply or heat it themselves would depend on the model.

Also our Asko dishwasher purchased about 5 years ago specifically has a hot water inlet, no cold at all.

From my own kitchen experience, hot soapy water removes oily/greasy deposits much better than cold soapy water. As for egg or cheese, I find the key is to get it rinsed off the plate before it cools, dries and sets. There is a good reason egg white is used in making up traditional artist's paints, it sets beautifully!

I think some confusion comes about with most modern clothes washers. We recently upgraded when our 14 year old simpson front loader died. The Bosch replacement only has cold water inlet unlike our old machine which had hot & cold inlets. Now the salesman in the store said (so take that as you choose...) it is because hot water supplies these days are so far away from the washer that they get too much cold water at the start, so just design them to allow for heating cold water as needed.

I reckon it's a matter of cheaper manufacture only having inlet components & valves needing to cope with cold water. As for making their energy ratings worse, I wouldn't be surprised if that was true.

However, we made sure that our new washer could select cold wash (no heating) on most wash programs, just like we used to run cold washes on our old machine.

If you are on a remote power system and relying solely on solar, then a dishwasher is probably considered a luxury by a lot of people. Best to check how much power it actually uses on a cycle (from manufacturer) and how often you will run it and factor that into your overall system capacity and usage.

As for using hot water, you may be able to run hot-ish water into it (that doesn't degrade the inlet workings more rapidly) and reduces your heating requirements, but I would be checking actually how much power it uses because it may not be that much after all.

Re: dishwashers

PostPosted: Wed Sep 01, 2010 8:13 pm
by toldminer
Andykidd. We have a pair of F&P dishdrawers. Mostly just the two of us here in SEQ and we normally run one of the drawers each day. Sometimes more often, sometimes less. I recorded the power used by them over a period of 27 days and together they would draw 102 kWhr per year. Seems quite small to me. The water pump from the tank water supply uses more. Our total power usage is about 8 kWhr/day and we produce about 11 (less lately with cloudy short days) use about 3 of our own, sell about 8, and buy about 5 of 100% green power. My overall aim is to reduce my carbon footprint as low as possible.

They are connected to the hot water that is supplied by our Solarhart system through the standard tempering valves that take the temperature down to 50 degrees max at the dishwasher. Lots of time during winter (particularly this year with lots of cloudy days) the temperature would be below that as the system does not go that high and I have a manual electric boost on it. I boost it when required, enough to give hot showers >35 degrees (which is required to get the Watersave valves open anyway, otherwise it is a cold shower).

I've considered feeding in the water that is tempered only to 70 deg to reduce the power used by the dishwasher heater at least in summer, but F&P have (I think) a 60 deg limit on the inlet temp. I think the small amount of power saved would not be worth the risk.

We generally prehandscrub egg covered plates etc in cold water. Generally the F&P works well. Just need to be careful not to squash too much in in too many layers. No breakdowns yet after 2 years of use. They don't have a good reputation for going a long time without attention. The good thing about the dishdrawers is you can just about live out of them without unpacking much to a cupboard. One clean getting emptied and one dirty getting full. We don't but I would if I lived alone.


Re: dishwashers

PostPosted: Thu Sep 02, 2010 10:02 am
by andykidd
Thank you all for your insights and experiences. I can add a bit more from my research:

The F&P technician who advised me does have his hot water plumbed into the only (usually cold) inlet at his home, with the recommended temp not exceeding 60 C , so as to not melt the seals.(I think I made a mistake saying at least 60 C). He also said egg and cheese were the only problem, avoided by rinsing them first.

His reason given for no longer having two inlets was that with energy rating now required, they cannot account for the energy going into heating the water externally, so they have to make machines that heat the water themselves for accountability.... and in the next breath he agreed that this is less efficient in cases like mine when I have solar hot water with instant gas boosting already nearby with short pipes between!

A friend disables the drying cycle on his eco setting and the dishes dry without the drawer having to be opened.

I am not sure how a mechanical model is more efficient if it still heats cold water?

I can refer you to this article about the way energy is used in the washing cycle:

I really appreciate all your input. Yours, Andy Kidd