Solarimmersion installed - Really need some help installing a de strat pump

[j2d]

I recently installed a Solarimmersion unit to work with our 4kw PV system.

The hot water tank is 1050mm high and I have just fitted a 27" immersion heater (as the old one was only 11")

I have also added an immersion jacket to the existing foam covering over the tank.

I've moved the cylinder stat up to just above the bottom of the 27" immersion heater, and the hot water is set to come on for 30 mins early morning and 30 mins late afternoon.

Cylinder stat set to 50 degrees, immersion set to abt 65 degrees.

The idea is obvious - I won't need to use the gas boiler while the weather is nice. But this still only means 2/3 of the tank will ever get heated unless the cylinder stat kicks in.

The solar immersion is designed to be used with a de strat pump, which I would really like to make use of, but I haven't got an idea of what I need and how to do it, even after searching google for 2hrs im none the wiser..

I have been reading a washing machine pump would do the job, is this correct?

Any help would be greatly appreciated

John

 

[The Solar King]

Are you sure you need to run a destrat pump? You may already have sufficient in the tank for your daily needs. Firstly, do you know what your daily hot water usage is at normal outlet temperature? This is unlikely to ever be above 45degC. Most calculations work on about 40ltrs per person per day. SAP works on considerably less, 25N+36 where floor area is unknown (SAP works on an outlet temperature of 47degC).

At 450mm diameter, the tank will hold about 140ltrs. This means 140ltrs stored at 60degC would give you the equivalent of 200litres, or 2/3 of the tank will give you 132ltrs. The other thing to bare in mind is that when the water in a cylinder stratifies, it does not stop at the level of the heating element, it will also pass below it. This is why when sizing a tank for solar thermal up to 30% of the solar volume (Vs) can be counted as daily volume (Vd). It is possible you could still have an effective volume of 150litres if the water is stored at 60degC.

Incidentallly, is this a vented or unvented cylinder? If it is the latter, please be careful what you do with the thermostats, or get a qualified person with an unvented ticket to look at this for you.

 

[The Solar King]

One other point. When storing water at 60degC, (or at any temperature at which there is a scald risk to infants and others), it is important to fit a thermostatic mixing valve either at the point of exit from the tank or at each point of use.

 

[j2d]

Are you sure you need to run a destrat pump? You may already have sufficient in the tank for your daily needs. Firstly, do you know what your daily hot water usage is at normal outlet temperature? This is unlikely to ever be above 45degC. Most calculations work on about 40ltrs per person per day. SAP works on considerably less, 25N+36 where floor area is unknown (SAP works on an outlet temperature of 47degC).

At 450mm diameter, the tank will hold about 140ltrs. This means 140ltrs stored at 60degC would give you the equivalent of 200litres, or 2/3 of the tank will give you 132ltrs. The other thing to bare in mind is that when the water in a cylinder stratifies, it does not stop at the level of the heating element, it will also pass below it. This is why when sizing a tank for solar thermal up to 30% of the solar volume (Vs) can be counted as daily volume (Vd). It is possible you could still have an effective volume of 150litres if the water is stored at 60degC.

Incidentallly, is this a vented or unvented cylinder? If it is the latter, please be careful what you do with the thermostats, or get a qualified person with an unvented ticket to look at this for you.

Thanks for the info Solar King, I feel I could definitely benefit from a de-strat pump, 2 reasons, first being during this time of year once the immersion has heated 2/3s of the tank there is still plenty of excess PV available which at present will just flow back into the grid, whereas if I fit a de-strat pump the solarimmersion can be set to turn the pump on at a certain level which will then eventually give me a full tank of hot water at no extra cost, instead 2/3s of a tank.

The problem of only having 2/3s of the tank heated, is that with the kids having a bath, me and maybe the mrs both having showers, there isn't much hot water left, and if the wife decides to have a shower before work it will be before the solar has kicked in to reheat the water, and may possibly not be as hot as she wants it, whereas a full tank of hot water should be plenty.

Re which system we have, I believe it is a vented system as we have tanks in the loft.

So can anyone point me in the right direction of where to start with this de-strat pump installation?

John

 

[Gavin A]

a destrat pump should be pretty simple to sus out if you know what you're doing, but IMO it's really one of those things where if you have to ask the question then it raises serious doubts about your competence to carry the work out.

so for that reason, I'm ooot.

 

[Worcester]

A de-strat pump would either need to be bronze (usual in pumped hot water systems) stainless steel or high tmeperature plastic, it simply acts as a 'short circuit' betweeen the top (hot water outlet) and bottom (cold water inlet) of the cylinder. - It needs to be able to be able to be used in a 'potable water' installation.
Grundfos Comfort | Grundfos
or
Grundfos make a model PU.120 for example which is plastic bodied for potable water applications. You wont find it on the Grundfos website, the info is on the Euro Boiler Parts website. PU 120 Grundfos Pump 1 Plastic Body Replacement Grundfos Bronze Pump (It's not officially available in the UK as Grundfos UK don't talk to Grundfos EU )

Important note: You need to be a competent plumber to install and a competent electrician to wire in.

 

[Digon]

I fitted a 36" immersion and whole house TMV to my 150L tank and despite running at higher tank temps my system was still shutting off at around mid-day. Note the higher temps will give scale problems in hard water areas.
I looked at fitting a de-strat pump but found that fitting a second immersion (11") via essex flange to the bottom of the tank was a much easier and cheaper route in my case. Fitting the flange, although straight forward, is not something I'd recommend a diy'r try unless very competent.
I'm switching my home made diverter manually between the two immersions at the moment until I get the software to do it for me, but I think your unit could be set to change to the bottom immersion after the top immersion has been off for x-minutes.

With a de-strat pump during the winter you risk stirring the tank after heating the top of the tank when the sun is going down and ending up with a tank of luke warm water. With two immersions you will nearly always have the top of the tank hot enough for at least one bath in the winter and on good days the bottom immersion will increase that.

Despite my bottom immersion limiting at 65C instead of the 75C on the spec sheet it is still making a big contribution.
The attached graphs show two bath draws on the top immersion setup and two bath draws plus a next morning shower draw on the two immersion setup.
The temp sensors are located 8" from top, middle and 6" from bottom of my tank.

 

[Worcester]

Hi Dijon, looks like someone has a bath at 7pm and someone a shower at 8pm
I've PM's you with a couple of questions, as I also monitor the cylinder using openenergymonitor.org products.

 

[Digon]

Hi Dijon, looks like someone has a bath at 7pm and someone a shower at 8pm
I've PM's you with a couple of questions, as I also monitor the cylinder using openenergymonitor.org products.

They are both quite large 7pm and 8pm bath draws but they look very different due to the different temp distributions at the start of the first bath. Only the top and btm immersion graph shows the much lower draw from a shower at about 7:45am.

 

[Digon]

Here is another graph screenshot taken a few minutes ago. It shows the tank heated on the top immersion until 12am and then switched to the bottom immersion. I am now going to switch it back to the top to use the remaining sun to top up the top of the tank. Note that it has been limiting since about 3pm even on the btm immersion

.

 

[j2d]

Hi,

Thanks for the info, fitting a second immersion (11") via essex flange to the bottom of the tank is definitely something worth considering and would definitely solve the problem of only the top half of the tank being heated, the solarimmersion can be wired to control a second immersion too, when the 1st has reached its temperature.

I still have the 11" immersion I removed to change for a 27" version, so I can re use that too.

My question though, how can you fit a flange and immersion heater to the bottom of the tank if the coil inside the tank is at the bottom too, wouldn't this be in the way?

Any links to the actual Essex flange I would need?

John

 

[Digon]

Hi,


My question though, how can you fit a flange and immersion heater to the bottom of the tank if the coil inside the tank is at the bottom too, wouldn't this be in the way?

Any links to the actual Essex flange I would need?

John

Good point,
I fitted my immersion between the bottom coil and the next coil up but it was difficult to do without them being in contact which I though might cause galvanic corrosion between the coil and the immersion. Basicallly I drilled the pilot hole through the tank then stuck an electricians screwdriver through the hole to determine the position of the gas heated coil then lifted the pilot hole an inch to get the best position between the coils. This might not be the best way to do this but it worked for me. YMMV and all that. It might be more sensible to drill just above the externally heated coil but then the immersion won't be right at the bottom of the tank.
I used the mechanical flange and 11" immersion from toolstation because they where about as cheap as I could find and also because I had one within driving distance of me.

http://www.toolstation.com/shop/Mechanical+Flange/p38614

 

[j2d]

Good point,
I fitted my immersion between the bottom coil and the next coil up but it was difficult to do without them being in contact which I though might cause galvanic corrosion between the coil and the immersion. Basicallly I drilled the pilot hole through the tank then stuck an electricians screwdriver through the hole to determine the position of the gas heated coil then lifted the pilot hole an inch to get the best position between the coils. This might not be the best way to do this but it worked for me. YMMV and all that. It might be more sensible to drill just above the externally heated coil but then the immersion won't be right at the bottom of the tank.
I used the mechanical flange and 11" immersion from toolstation because they where about as cheap as I could find and also because I had one within driving distance of me.

Toolstation > Heating > Central Heating > Mechanical Flange

I think this is definitely the best route for me, as I already have a spare 11" immersion heater, just need to get hold of the correct flange and have a look inside the cylinder to see if I can fit can fit the immersion at the bottom between internal coils.

Has anyone got any info on the internal coils of a 1050mm high cylinder? do they go all the way to the bottom? Whats the gap between coils?

John

 

[Worcester]

Has anyone got any info on the internal coils of a 1050mm high cylinder? do they go all the way to the bottom? Whats the gap between coils? John

Every make of cylinder will be different! Even the same make made in different batches will vary...

 

[j2d]

Good point,
I fitted my immersion between the bottom coil and the next coil up but it was difficult to do without them being in contact which I though might cause galvanic corrosion between the coil and the immersion. Basicallly I drilled the pilot hole through the tank then stuck an electricians screwdriver through the hole to determine the position of the gas heated coil then lifted the pilot hole an inch to get the best position between the coils. This might not be the best way to do this but it worked for me. YMMV and all that. It might be more sensible to drill just above the externally heated coil but then the immersion won't be right at the bottom of the tank.
I used the mechanical flange and 11" immersion from toolstation because they where about as cheap as I could find and also because I had one within driving distance of me.

Toolstation > Heating > Central Heating > Mechanical Flange

Hi Digon,

Thanks again for the info, I think i'm going to give this a try.

That link to the immersion heater flange from toolstation, does it come with washers? is that item all I need (38614)?

Is there any difference between that and the immersion heater Essex flange (other than the price!)

http://www.amazon.co.uk/gp/product/B008C8T9CW/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=103612307&pf_rd_s=lpo-top-stripe&pf_rd_t=201&pf_rd_i=B008C8T990&pf_rd_m=A3P5ROKL5A1OLE&pf_rd_r=1328J7R5GHS5BNC7EYEJ

Thanks again

John

 

[Digon]

Hi John,
The flange in your link looks like an angled one like you would use on the top of a tank and also it has two cork gaskets compared to Toolstations single included fibre gasket. They both do the same job.
Other things you might need are a second gasket for inside the tank if you are struggling to get a seal, don't know if this is a good idea other than as a last resort though. 'Boss white' to smear on the gasket faces may help. I always thought using BW was a sign of the job having been bodged but In this instance I used a bit.:bucktooth:
Make sure you have a big enough spanner or Stillsons to tighten the nut with!

Dave

Spare gasket Toolstation > Heating > Central Heating > Mechanical Flange

Boss White
Toolstation > Plumbing > Consumables > Boss White

 

[SPARTYKUS]

Whats peoples ballpark for a TMV and its fitting? We have solar water fitted 1992!!!) and the water sometimes gets into the 90's. been told they over egged it a bit in those days as not sure on performance ( have six panels).

 

[The Solar King]

Good quality 22mm TMV should cost £60-£65.00. You can find cheaper ones if you wish. Fitting cost will depend on how much draining down is necessary. As long as there is some form of stop valve on the hot tank inlet, it shouldn't be too much.

From a safety point of view, it is really important you get this sorted. Burns from scalding water are stomach turning. In Scotland you are now required to fit a TMV to the bath on all new build or when upgrading a bathroom.. The ideal solution is to fit TMVs at each point of use. In that way you can ensure best use of water and maximum safety. You can do things like set the temperature on a wash hand basin at something like 41degC, as most people wash hands (if they bother) under a running tap. 15mm TMVs are lot cheaper - £30-35.00

When you say 6 panels, what size are they, what is their total area and how big is your hot water cylinder? Reason for asking is if your cylinder gets hot pretty early on, the system will shut off and the panels stagnate. The circulation fluid in the panels then gets very hot (as high as 200degC) and over time degrades. This means you need to have the circulation fluid changed more often. Some systems have a glass flow meter. If you can see the fluid has darkened or looks at all gungy, it definitely needs to be changed.

One other point. Your system should be shutting off when the bottom of the cylinder reaches around 60degC. Is there a possible fault with the sensor or controller?

Shame you aren't in East Central Scotland, would have been happy to sort you out.

 

[j2d]

Hi John,
The flange in your link looks like an angled one like you would use on the top of a tank and also it has two cork gaskets compared to Toolstations single included fibre gasket. They both do the same job.
Other things you might need are a second gasket for inside the tank if you are struggling to get a seal, don't know if this is a good idea other than as a last resort though. 'Boss white' to smear on the gasket faces may help. I always thought using BW was a sign of the job having been bodged but In this instance I used a bit.:bucktooth:
Make sure you have a big enough spanner or Stillsons to tighten the nut with!

Dave

Spare gasket Toolstation > Heating > Central Heating > Mechanical Flange

Boss White
Toolstation > Plumbing > Consumables > Boss White

Thanks again for your help Dave, I'm going to order that flange tonight and hopefully get this done at the weekend, couple more questions for you -

Does that flange include a locking nut?
How did u get the locking nut inside the tank? By removing the top immersion heater I'm guessing?
With the tank having a slight curve would/did this cause u a problem getting a seal on the new flange?
What size hole did you need to drill to fit the flange, I'm guessing its best to keep it as small as pos to get the best seal.

Sorry for even more questions

John.

 

[Digon]

I used a 64mm holesaw Toolstation > Power Tool Accessories > Holesaws > Bi Metal Holesaw
I already had the arbour to fit it to. The 64mm cutter will cut the hole slightly undersize. I then used a rotary file in a cordless drill to ease the hole out until the threads of the flange just passed through. The hole is then opened out further at the 3 and 9 oclock positions until the flange can be just pushed through and into the tank. Go steady because if the hole ends up being a slack fit it won't seal. The flange is pulled back so the threaded boss sticks out through the hole and then rotated 90deg so the wider part of the flange sits behind the wider part of the hole and the gasket and included locknut is fitted outside and tightened. The curvature of the tank will be flattened out locally as you tighten the flange.
The flanged part that fits inside the tank is circular with two sides cut off so its more of an oblong shape in plan view.
Its difficult to explain but once you see the flange it will become obvious.