Hot water preheat tank for instantaneous gas system

[Warpspeed]

Because If I am using a LOT of hot water, my storage would quickly be depleted if the temperature was set very low.

The whole hot water system here is something I plan to look into in the future. I would like to get more solar panels and transfer much of my heating load onto solar. First thing will probably be a hot water preheater.
Many possibilities, but surviving on a pension does limit what is possible short term.

 

[rogerdw]

I put in one of these mixing valves to at least have the max temp be < scalding. Seems to work reasonably well, isn't hard to install and set, and is easy to adjust.

Looks like a very handy device.

So is there any reason I can't fit a preheat water tank set to 60C (for safety from Legionaires) ... and fit one of the mixing valves on the outlet set to reduce to say 35C ... a few degrees below the lowest expected outlet temperature ... then let the gas bring it back up to the dialled in temperature ... 39-46C ?

If my initial inlet into the preheat tank is say 8-10 degrees ... and that is heated with the free solar power ... it would have to reduce our gas bill considerably surely ... ie. the gas only has to bring it from 35-39 and not 10-39 degrees.

If it gets to a stage where the min temp required is higher ... we can just wind up that mixing valve ... eg if MIL moves into a nursing home.

 

[plympton]

Looks like a very handy device.

So is there any reason I can't fit a preheat water tank set to 60C (for safety from Legionaires) ... and fit one of the mixing valves on the outlet set to reduce to say 35C ... a few degrees below the lowest expected outlet temperature ... then let the gas bring it back up to the dialled in temperature ... 39-46C ?

If my initial inlet into the preheat tank is say 8-10 degrees ... and that is heated with the free solar power ... it would have to reduce our gas bill considerably surely ... ie. the gas only has to bring it from 35-39 and not 10-39 degrees.

If it gets to a stage where the min temp required is higher ... we can just wind up that mixing valve ... eg if MIL moves into a nursing home.

Actually, if you read the product page, Mixing valve info page, that's exactly the scenario they describe (even the temp!).

The problem is that you'll have to feed it fresh cold water to get it to the 35c, so if you're concerned about bugs in the fresh water line, you're just re-introducing them into the mixed output. It has to thin that somehow.

 

[Warpspeed]

Looks like a very handy device.

So is there any reason I can't fit a preheat water tank set to 60C (for safety from Legionaires) ... and fit one of the mixing valves on the outlet set to reduce to say 35C ... a few degrees below the lowest expected outlet temperature ... then let the gas bring it back up to the dialled in temperature ... 39-46C ?

If my initial inlet into the preheat tank is say 8-10 degrees ... and that is heated with the free solar power ... it would have to reduce our gas bill considerably surely ... ie. the gas only has to bring it from 35-39 and not 10-39 degrees.

If it gets to a stage where the min temp required is higher ... we can just wind up that mixing valve ... eg if MIL moves into a nursing home.

That should all work pretty well.

I think this whole Legionnaires thing is totally overblown.
If the risk was as high as some people believe, people drink and wash in cold water and are not dropping dead.
Bugs do not spontaneously manifest in a water tank from nowhere, they have to get in there somehow.
In the tropics, water coming out of the COLD tap might be at the supposedly dangerous 30 to 40 Celsius ambient temperature range, and people are not dropping dead from Legionaries there either.

Legionaires is definitely a problem in cooling towers, where fully exposed warm water splashes through the air and is exposed to sunlight and can pick up anything floating around in the air. The fine mist created can then get into your lungs where the bugs then breed.
But a closed and totally dark water tank is very different to the open sump in a cooling tower.

 

[rogerdw]

Actually, if you read the product page, Mixing valve info page, that's exactly the scenario they describe (even the temp!).

The problem is that you'll have to feed it fresh cold water to get it to the 35c, so if you're concerned about bugs in the fresh water line, you're just re-introducing them into the mixed output. It has to thin that somehow.

Thanks for pointing that out. Encouraging.

And no, I'm definitely not worried about bugs in the water being fed in to the cold side ... it's the same water we drink and use in the house from the rainwater tanks ... and have been for years.

I think this whole Legionnaires thing is totally overblown.
If the risk was as high as some people believe, people drink and wash in cold water and are not dropping dead.
Bugs do not spontaneously manifest in a water tank from nowhere, they have to get in there somehow.
In the tropics, water coming out of the COLD tap might be at the supposedly dangerous 30 to 40 Celsius ambient temperature range, and people are not dropping dead from Legionaries there either.

I am inclined to agree. I know lots of people are horrified but it seems to be an Australian thing to have rainwater tanks and use that water for everything. Certainly prefer that to what comes in the mains supply with all the crap they put in it. We're on a dead end road and there have been times our mains water has been thick and gluggy ... with a gel like substance in it. Now that's truly horrifying. Almost too frightened to put it on the garden.

Having said that, I can see it being worthwhile getting the preheat tank up to 60C+ so that if we go through a big batch, it doesn't get cooled too quickly by the incoming cold just like you mentioned. Depends on how big it is of course.

 

[Zwy]

HPHW much more efficient than tankless. Also easier to use on a solar setup.

I agree and there is storage for days of limited sun.

HPHW draws so little power. Mine takes between 2 to 3.5 Kwhaverage per day depending on how much laundry and dishwasher (I run hot water into the dishwasher). Yesterday she did 3 loads of laundry, ran the dishwasher too. 5.6 Kwh for the day.

I have a propane tankless in the shop, it is a great use for it, I run the hot water thru a pressure washer. I always thought of going tankless in the house, but after buying a HPWH, there is no way I'd go with a tankless. I run in series with the original propane and that gives 100 gallons of hot water.

 

[Warpspeed]

You can get pretty effective water filters, and there are also ultraviolet sterilizers that will remove or kill most of the nasties.
Its only really the kitchen water that needs to be really good.

 

[rogerdw]

I run in series with the original propane and that gives 100 gallons of hot water.

Hang on ... so at your house you have your new HPHW feeding into your original propane hot water tank? ... which is just used for additional storage? ... or gas heats that to keep it up to temp?

You can get pretty effective water filters, and there are also ultraviolet sterilizers that will remove or kill most of the nasties.
Its only really the kitchen water that needs to be really good.

Yeah we do have a filter in the kitchen.

 

[Supervstech]

That should all work pretty well.

I think this whole Legionnaires thing is totally overblown.
If the risk was as high as some people believe, people drink and wash in cold water and are not dropping dead.
Bugs do not spontaneously manifest in a water tank from nowhere, they have to get in there somehow.
In the tropics, water coming out of the COLD tap might be at the supposedly dangerous 30 to 40 Celsius ambient temperature range, and people are not dropping dead from Legionaries there either.

Legionaires is definitely a problem in cooling towers, where fully exposed warm water splashes through the air and is exposed to sunlight and can pick up anything floating around in the air. The fine mist created can then get into your lungs where the bugs then breed.
But a closed and totally dark water tank is very different to the open sump in a cooling tower.

I mean... municipal water is in open tanks thats pumped up to water towers, and piped through the city...

Well water is earth filtered rainwater...

How do you think the water arrives in the pipes?

Of course a stagnant tank, or run of piping can develop a colony of the bacteria. Why do you think firemen flush their hydrants regularly? What do you think brackish water means?

Is it MORE prevalent in a tank with air flowing over it? Of course. But it CAN build up in a water storage tank.

Would i worry about it? Coming from shower tap? Nope... i dont drink from the sink or showerhead with hot water...

 

[Zwy]

Hang on ... so at your house you have your new HPHW feeding into your original propane hot water tank? ... which is just used for additional storage? ... or gas heats that to keep it up to temp?

Additional storage plus I'm guaranteed a minimum hot water temp during periods of extended cloudy days. I can turn the HPWH on/off with the app on my phone, set up a schedule and change water temp so it might only preheat the water.

Originally I was looking for a dump load but really the HPWH uses such a small amount of power the only time it isn't on is when bad weather sets in for a week.

 

[rogerdw]

Additional storage plus I'm guaranteed a minimum hot water temp during periods of extended cloudy days. I can turn the HPWH on/off with the app on my phone, set up a schedule and change water temp so it might only preheat the water.

Originally I was looking for a dump load but really the HPWH uses such a small amount of power the only time it isn't on is when bad weather sets in for a week.

Thanks for the explanation. I shall mull it over for a while.