Solar panel, thermal store and electric showers...

[strawberryzoe]

Hello All!

Apologies if this has been posted before but I don’t seem to be able to find a response.

My partner and I are currently doing up our 1840s cottage and are planning on putting up a solar panel to provide our DHW in the summer and use our existing wood burner to heat the water and the house in the winter. The existing WBS system heats a 120l cylinder which is topped up via an electric immersion heater. We have no gas available and I don’t really want to put in an oil tank.

From what I have read, it seems the most sensible thing is to do is to install a thermal store (although I’m not sure where it will go as it will probably have to be quite large) which will provide hot water at mains pressure when the sun’s shining or the wood burner is on. In the spring and autumn however it would be likely to require topping up so we plan to install an electric immersion in the thermal store so if needed it can heat that up.

My concern is that this will require a huge amount of electric energy to heat this huge volume of water for what will essentially be providing showers, the occasional bath and hot water to taps. So my plan was to install an electric shower which will take this “pre-warmed” water at mains pressure and heat it further if required. I will obviously need a tmv to set a maximum inlet temperature to avoid scalding in the shower however this system should use less electricity but still guarantee a hot shower when the thermal store isn’t hot.

My concerns with this are:
1.   Will the tmv reduce the pressure so it can’t be used with an electric shower?

2.   Is it best to revert to a normal cylinder rather than a thermal store to heat less of a volume of water?

3.   If a “normal” electric shower arrangement with a cold mains feed is used instead, then I don’t think it’s worth installing a solar panel at all just for hot water in taps.  Will the net benefit of the solar be worth it (I don’t expect this question to be answerable!!)

Any help would be gratefully appreciated. I’m new to the whole thing so feel free to point out the blindingly obvious!!

Many thanks,
Zoe 

[Rooster]

On the shower side of things .....

Ordinary electric showers aren't designed to take 'pre-warmed' water.

There are however some that accept pre-warmed and then modulate the heater to suit thereby saving electricity.

One example is the Zip http://www.tlc-direct.co.uk/Products/SOILX009.html

[dhaslam]

The most cost effective way to top up the temperatures using electricity is to use off peak electricity.  This means having enough storage  to  have the water hot during the day without having to top up.    Of course the large  cylinder or thermal store is needed for solar anyway  because  hot water has to be stored overnight.    I use about 14kwh per day for water heating and solar  has only averaged 4.8 kwh per day in October, while the stove isn't needed yet for heating.  However the  water is mostly heated using the heat pump and off peak  electricity with about 1-2 Kwh of immersion to reach the last few degrees.   

[strawberryzoe]

Thanks for the responses.

Rooster, I have seen this inline heater recommended elsewhere for a similar problem. Have you got one of these installed or have used one before? What's the pressure like? I'm concerned that whilst we'll get mains pressure out of the thermal store but that this will be reduced and won't be useable for a shower?!

 

[dinitro]

Hi

I have an Mira 9.6 Kwh? shower connected to my thermal store.

It is connected after a tmv so that prewarmed water enters the shower.

Problems: in summer when the thermal store temp is higher and the cold mains if warm the shower
reports a service fault that is easily rectified by switch the powersupply on and off.

Problem2:due to a 15mm piperun the shower suffers from low pressure when hot water outlets draw water.

The first can be 'even further fixed' by adjusting the tmv for lower input temp.  The second by changing the
supply line which I plan to do this summer.

Regarding whether electric showers can be fitted to thermal stores/ solar I think manufacturers are just covering themselves.
I have a temp gauge on the rising main and temp can be between 6 degrees 20 degrees.  If you prewarm to 20 degrees its still a substantial
saving.

dinitro

[lightfoot]

Hi Zoe,

It may not directly answer your question, but for the record - depending what you require from the system and the size of the WBS etc, the thermal store may not necessarily need to be huge.  Also, if you heat the store from the top down (the hot water will float on top of the cold water), then you don't have to heat the entire store if you only require a small amount of DHW in the summer etc - this is one of the reasons to use a loading valve etc on the WBS circuit etc.  

Depending on the size of your system, for the solar input this can be achieved by using coils at different heights in the store - heating the upper part first and then diverting to a lower coil etc, or you could use some other form of stratifying device/method, such as a side-arm heat exchanger etc etc.  You could also opt to have a couple of immersion heaters at different heights too, if there's not sufficient solar gain and/or you don't wish to light a small fire in the WBS etc.

[Rooster]

Thanks for the responses.

Rooster, I have seen this inline heater recommended elsewhere for a similar problem. Have you got one of these installed or have used one before? What's the pressure like? I'm concerned that whilst we'll get mains pressure out of the thermal store but that this will be reduced and won't be useable for a shower?!

 

I don't have one but am considering getting one.

Some others on the forum do though, KLD and pt,.... see this thread ..... http://www.navitron.org.uk/forum/index.php/topic,4897.0.html

[Mudman]

I wonder if you’ve considered preheating the incoming water using a waste-water heat exchanger? I've seen a couple of these available- posted a link on the forum to one in the Netherlands company a couple of weeks ago and can dig it out maybe- I’ve been interested in these devices for a while as it seems such a waste to let the hot water from your shower heat the sewers when some of it could be recovered.
I saw a vertical waste pipe with copper incoming water pipe wound round it in the states and this Netherlands company use an almost horizontal arrangement under the shower tray to exchange heat with incoming water.
You could either have this incoming waste-water-heated water coming into your DHW system or into the input for the electric shower but it sounds from this topic’s discussion like many electric showers don’t allow for very warm water input. You’d only benefit from the times that the shower was running though.
Ben

[spluger]

i made my own waste water heat recovery system,
had copper waste on the bath so i wound the cold feed t the thermostatic shower around this using 2 x 10mm copper pipes for about 2 foot.
haven't measured the temp gain but it feels warmer to the touch

this would give a better flow rate to a normal electric shower as the heat output is dependant on the flow rate
have you noticed how in the summer you can have a better flow rate and in the winter the temp needs turning up!

on most electric showers all that preheating the incoming water will do is give higher temps or if you turn the temp down better flow rates. unless the preheat is enough to use the lower power settings on the shower?


David

[Mudman]

very interesting, David- is that two feet of waste pipe or the wound 10mm? if it's the waste pipe, do you know how long your 10mm pipes are?
any photos?
one apparent advantage of the vertical pipe arrangement i'd seen was that waste water tends to flow down the outside of a vertical pipe, so most of it's closer to the incoming water- just thinking most of the hot waste water in your pipe would be at the bottom of the waste pipe - did you take any steps to help make the most of that?

Ben

[KLD]

Thanks for the responses.

Rooster, I have seen this inline heater recommended elsewhere for a similar problem. Have you got one of these installed or have used one before? What's the pressure like? I'm concerned that whilst we'll get mains pressure out of the thermal store but that this will be reduced and won't be useable for a shower?!

 

The limiting factor re: "usable for a shower" with the ILX9 is not the inlet pressure, but the maximum electrical output power. Depending on the inlet temperature, the available 9kW are not enough for one of those fast-flow rain showers. That said, if you are confident that you always have prewarmed water at, say, 25 or 30°C, then you should be fiiine. The electronics in this device limit the output temp by modulating / switching-off the heater element. They do not regulate the flow!

Klaus

[spluger]

mudman

its 2" for the waste pipe and it runs horizontal
the 10mm was in 2 runs in parallel to help with the flow rate as it squashed oval while winding total length about 5" x 2
I'll get some photos when i referb that bathroom and I'll improve the contact by soldering the 10mm onto the waste and wrap in silver foil tape.
i seen some on eBay and webs site selling for $200 !!!!

only prob is I'm fitting an on suite shower and there's no Chance of doing the same. i did think about running a 10mm inside the plastic waste but think it could major problems if it leaked under the shower tray

how ever what do you guys think about running the incoming mains up and down inside the main sewer vent pipe? this takes all waste from both main bathroom and on suite and the mains in is the other side of the wall so only a few holes to drill???
might need an insulated pipe to prevent freezing though

[pt]

Sorry I've only just seen this. Follow http://www.navitron.org.uk/forum/index.php/topic,4897.msg48069.html#msg48069. I had the same dilemma and installed the zip inline on a mains pressure feed from the heatstore. Just what I wanted - tops up the incoming hot water to the desired temp. I don't know the figures but I suspect 9kw for five minutes will be cheaper than 3kw of immersion for however long it takes to heat up a large heatstore. Add to that the convenience of a hot shower always available and I'm happy with the set up. Let me know if you need any further information.

[brackwell]

pt

I have been wanting to use the ILX9 but i have a low pressure system and i am concerned about pressure drop through the unit itself. Although i guess you know that you can remove the flow restrictor built in.  Zip in about a months time will have a new model designed for just this use-called DBX but no other details released unless someone else does. 

Although Zip say not to be used with input temp above 30C this is only because the German manufacturers do not have "the certificate "

Any way glad to hear you are a enthusiast for the system as i am sure that this is a real way forward. You drastically understate the benefit however as the unit only uses enough electricty to reach the desired temp. For most months it will not be using any elec and only when the thermal gets down to 24C at 10L/min will you be useing the full 9Kw.

Ken

[pt]

One other point it might be worth bearing in mind at the planning stage. Because the unit has such a high potential powerdrain (9kw)  it requires a separate heavy duty supply cable ( can't remember exact spec but its about as wide as my thumb), and dedicated fuse with RCB. The cable is almost impossible to bend to tight angles so the easier you make the run the better. Brackwell -  Regarding removing the flow restrictor, the outlet pipe from the heating element has an inside diameter of no more than 10mm so I don't think you'd get sufficient flow from a low pressure input for a satisfactory shower. You do right to wait for the dedicated low pressure model. Strawberryzone - the flow from our mains  pressure system is fine for a 50mm showerhead, but yes, the unit does slow down the flow. It also struggles with very cold water. However, we use the heatstore as a buffer in the winter (ie run the central heating flow through it), and in the summer the tank is always kept at least warm by the solar panel, and low temp has never been a problem. This set up meets the requirements of two rugby playing teenagers and a wife with long, thick hair that takes a lot of rinsing, so I get a quiet life!