Hot water circulation system

[Wetkit]

Hi Guys,

 

Been thinking of doing a circulation system for my hot water.

 

Currently I only have the one 200L geyser which is on the roof.

I have 2 bathrooms directly below it.

Kitchen is about 12m away.

All hot water piping is 22mm copper. The size is so big as we had a gravity fed system some 15 years back.

 

I was thining of putting in a 2nd loop from the kitchen back to the inlet of the geyser with a small pump.

This way the water is the pipes should always be hot.

Yes, I will insulate the pipes.

I know it would use more energy, but is should also save on water consumption.

At this moment the taps is run for ages before the hot water gets out the taps.

 

Think it would work?

Anybody have a similar system that would care to comment?

[Energy-Jason]

Hi Wetkit,

 

This looks like a great project,

Would a thermosyphon system be able to be of use here?

Regards

E

[Wetkit]

I can not think of anything why a thermosypen system should not be able to work.

 

My biggest concern is how much heat energy I will loose in the pipes with circulating the water.

Perhaps make all the lines 15mm copper, or just the return line, or change everything to polycorp?

[danielbotha]

Why do you want to circulate the water?

If you want to save electricity, forget it!

If you just want the water from the tap to be warm faster, go ahead.

 

Here is some info and ideas that might help.

Whatever I did was to save electricity. 

1: My Kitchen is also about 12m from the geyser.  I also have 22mm copper piping.

I have a "braai" room back to back with my kitchen. I installed a 12L gas "geyser" in the room.  I used 15mm pipe and the run is 1,5m from the gas geyser to the kitchen basin.  That elliminated the enerygy wasted.  The gas geyser works like a dream.  The water flow of gas geysers is not great but for a basin or shower it is fine.

2: I installed a Heatpump.  Heatpumps are very efficient in heating water.  Heatpumps also make use of a circulation pump.  I connected my two 150 Liter geysers in a loop with the heatpump.  The water is pumped from the heatpump to geyser 1 inlet, geser 1 outlet feed geyser 2 inlet and geyser 2 outlet is fed back to the heatpump as well as to  two bathrooms. 

I have measured the power consumption of my geysers in the past over many months.  The consumption was an ave of 16kWh/day.

My ave so far with the heatpump is 6kWh/day.

 

Regarding your idea.  Remember that the circulation pump must be able to handle both the pressure and heat.  If you use a heatpump you can utilise the pump in the heatpump for your circulation circuit.  What you will need to do is to modify the system and supply power to the pump constantly.  You can extend the geyser /heatpump loop to run to the point where you want "instant" hot water.

 

In my system I used 22m Pex pipe  (rated for 95 deg).  It has better insulation properties than copper and bends very easily. 22mm is prescribed by heatpump suppliers. The inside diameter is less that that of copper because the wall is thicker. You are not suppose to use polycop for hot water.  I have logged temperatures at different points in my system.  At 3 points I measured the temperature between the pipe and the insulation around it. The temperature drop from 52deg to 32deg in 40 minutes at an ambient temp of 14deg.  You will lose a lot of energy. Copper will lose even more compared to Pex pipe.

 

I dont think thermosyphen system will work. For the thermosyphen to circulate you need water to cool(or heat). You need a one-way valve or else you will get "cold" water from the "cold" section of the thermosyphen loop fed back to your bathroom. The one way valve needs "some" presure to let water through.  A thermosyphen have equal preassure on both sides of the valve.... no flow.

 

I an NOT a plumber and NOT an expert but I do have SOME experience and a good understanding of physics.

 

 

 

If you want some graphs, let me know.

[Clint]

Daniel what brand of PEX pipe do you use?

[Wetkit]

Hi Daniel, thanks for your comments.

Main reason I am looking at this is to reduce the amount of water I am using.

Say I am looking for 15L of water in the kitchen. It takes around 5L of cold water before the hot water gets to the basin.

So now I am looking at 20L of ice cold water going into the geyser.

With a 200L geyser, that is 10%.....

 

Mmmm, perhaps just adding the 2nd solar geyser should be enough......

 

I do have gas in my kitchen for the hob, but I do not have any wall space to mount a gas geyser.

The gas geyser for the 3rd bathroom shower works great!

[danielbotha]

Daniel what brand of PEX pipe do you use?

COBRA-SAFE MLP SYSTEM 22X2,5 PE-X-AL-PE-X CLASS2/ 10 BAR/ 95 DEG C

Thats what is written on the pipe

[danielbotha]

Hi Daniel, thanks for your comments.

Main reason I am looking at this is to reduce the amount of water I am using.

Say I am looking for 15L of water in the kitchen. It takes around 5L of cold water before the hot water gets to the basin.

So now I am looking at 20L of ice cold water going into the geyser.

With a 200L geyser, that is 10%.....

 

Mmmm, perhaps just adding the 2nd solar geyser should be enough......

 

I do have gas in my kitchen for the hob, but I do not have any wall space to mount a gas geyser.

The gas geyser for the 3rd bathroom shower works great!

I had the same issue in my kitchen.  Water was not my problem.  I am renting on a farm with ample free water.

ELECTRICITY is my issue.   The gas geyser solved that.

 

 

 

Another way to do it if electricity is NOT an issue is to install a small 10L underbasin geyser in the space under the kitchen sink. 

They look very nice and works well. 

http://kwikot.co.za/Products/Point%20of%20Use%20Water%20Heaters/Prisma%20Deluxe.php

 

How do you intend to use a 2nd solar geyser to save water?

[Wetkit]

How do you intend to use a 2nd solar geyser to save water?

 

Ideally i would like to not use ANY electricity for hot water.

Currently with only a single 200L geyser, if you shower once, all the added cold water into they geyser will cool it down.

Now the 2nd person to shower gets a luke warm one.

 

My idea is to have a second solar geyser feeding the first one.

So basically I have 400L of hot water and not 200L.

 

Also my existing solar geyser is nearly 8 years old. The flat plate is not as effective as the newer vacuum tubes and the pipes in the flat plate is starting to scale, so I would need to clean them too.

 

With the extra capacity of the two geysers, I can afford to run a loop through one of they geysers, meaning I circulte hot water through all the hotwater pipes.

By keeping the water in the pipes hot, you should have instant hot water when you open a tap.

50W solar powerd pump should do the job very well.

Piping could set me back a bit

[Clint]

COBRA-SAFE MLP SYSTEM 22X2,5 PE-X-AL-PE-X CLASS2/ 10 BAR/ 95 DEG C

Thats what is written on the pipe

Thanks

[Wetkit]

Ok, so here is the idea.

 

 

TV = Tempering valve (Still have to research this one a bit more, but basically a mixing valve that will output hot water at a constant temp)

VT = Vacuum tube

FP = Flate plate

 

Normal operation would be to run the hot water in a closed loop only through the VT geyser.

When water is consumed, hot water would be deliverd from the FP system.

Now I should be able to use 200L of hot water without any problems.

 

In summer the VT water could start boiling, so then the idea is to run the High temp pump, while the Normal pump is stopped.

I can then heat 400L of water via the VT and have the FP isolated. (Yes, will drain the water out of the FP so it does not explode due to internal pressure build-up).

 

What do you think?

 

Would also need to find some type of intelligent controller to control the pumps.

 

 

 

[Wetkit]

Eish, did it take this long to do???

 

So with increasing the PV on my roof, I needed more space.

So basically I had to swap the two solar geysers with my PV.

 

All the old copper 22mm piping was replaced with the Cobra 15mm white pipe. This pipe works well and can also use the normal copper pipe fittings.

Great advantage of these pipes is that they have way better insulation than the copper pipes.

Reason for going smaller pipe is also to have less water in the pipe, meaning less heat loss.

 

The single biggest problem I had with the automatic mixing valves (It is now law to install these with solar geysers) was the pressure.

Basically if the hot and cold water were at diffrent pressures, the mixing valve did not work correctly.

 

First option is to install the mixing valve right at the geyser output. This makes it easy as your cold water can be taken directly from the geyser feed.

Problem with this is that the "cooler" water output now from the geyser takes a hell of a long time to get the pipes heated till you get warm water at the tap.

 

2nd option was to install mixing valves at each hot water tap. Not only is this costly, but again there is problems with the water pressure

 

My 3rd option that did work was to use a single pressure valve to feed the geyser and the 2 mixing valves. I used 2 valves due to the distance between the kitchen and the bathrooms.

The single pressure regulator also feed a 2nd cold water line going to each mixing valve. This ensure that the cold and hot water pressure is the same at each mixing valve.

 

For now everything is working ok and nobody can burn themselves on the scalding hot water

Thing is, sometimes you want HOT water for washing dishes, or that extra long soaking bath.

Seems like 55C is safe, but just that tad too cold.

[Wetkit]

Here is what the 2 solar geysers look like now.

Both facing North and at 45 degrees.

Took all my math and trig skills to get it right!!!

 

[Wetkit]

Ok, just some feedback on the mixing valves.

Man, these things is a POS!!!

 

So, they have build in safeties, so if your cold water pressure drops away, no water will exit the valve.

Next problem I picked up was that if the cold water pressure is higher than the hot water, the cold water would actually start pushing back into the hot water line.

So you have to install a one way valve with each of the mixing valves as well

 

I spent the whole of Saturday in the roof trying to figure these issues out.

So for now I have removed the valve to the kitchen, so that water is a balmy 65Degrees now.

Bathrooms is still on a single mixer. That works really well now with the shower

[superdiy]

Ok, just some feedback on the mixing valves.

Man, these things is a POS!!!

 

So, they have build in safeties, so if your cold water pressure drops away, no water will exit the valve.

Next problem I picked up was that if the cold water pressure is higher than the hot water, the cold water would actually start pushing back into the hot water line.

So you have to install a one way valve with each of the mixing valves as well

 

I spent the whole of Saturday in the roof trying to figure these issues out.

So for now I have removed the valve to the kitchen, so that water is a balmy 65Degrees now.

Bathrooms is still on a single mixer. That works really well now with the shower

 

Hi Wetkit

 

The correct method of connecting your cold water to your taps etc is after the pressure control valve (T-junction between the pressure control valve and the geyser inlet).  If you connect your cold water feeding your taps, toilets etc. after your pressure control valve you will have balanced pressure at all your fittings.  Mixer taps will have the same pressure on hot and cold water and when somebody flushes the toilet the guy that showers will not start to burn. If you connect the "balanced" cold water supply to the "mixing valve" you will effectively add the same pressure cold water and hot water to it and you won't need check valves (one-way valves) in the hot water line.

 

If the existing plumbing's cold water taps are currently connected to high pressure and you cannot change it easily, you can still connect the "mixing valve's" cold inlet to "after the pressure control valve" to have the incoming hot and cold water pressure on the "mixing valve" balanced - then you still don't need a check-valve for the hot water line.

 

Since you will now have balanced pressure on the "mixing valve" all the time (hot and cold water pressure will always be the same), you will not run into the problem of having a "pressure drop on the cold water" as you described either.

[bmeagle]

Even if you're not circulating your hot water with a feedback loop pipe insulation even on PEX piping will help a lot with heat loss.

Do you guys typically use insulation on your warm water piping or not?

If you can feel the insulation on a geyser or pipe is warm then you don't have sufficient insulation on the pipe.

One would need to do a proper calculation to determine if it is worthwhile to recirculate the warm water in well insulated piping to compare the circulation energy cost vs heating the extra cold water you are pulling into your geyser.

[Sidewinder]

I have more or less same scenario: long distance to scullery from geyser. 22mm copper pipes. So I use a few 5l plastic bottles, stored underneath the sink. Then those 5l of cold water is used to water my potplants outside by hand. Everybody that draws hot water at the sink has standing instructions to fill the bottles! 

 

Bit of a schlepp, but is my short term solution.

[Guest]

I had same problem.

 

So I bought a 2nd hand 50l geyser for just the kitchen and spare room shower. Hardly noticed any increase in electricity, and no more wasted water waiting for the hot water.

 

200l geyser, Had the same problem re. 3rd and 4th person showering. If I can redo it, I would go for 400l.  

 

On my 200l I use about 2 hours Eskom per day in winter. In summer I do not use any Eskom to heat up the water.

 

Yes, there may be some dictatorial decisions involved re. shower times and for how long. SWAMBO was the toughest nut to crack.   

So it took a few weeks to get all family members in line but once the savings where noticed, and it was substantial, it became a non-issue.

Should have gone for the 400l geyser.