How to maximise

dots03

I am looking for advice on how to more efficiently utilise our solar set up at home. I am not a plumber so please excuse my use of laymans terms and for the lenghty post.

We have 20 solar tubes hooked up to a Resol Deltasol BS controller + a 280 litre tank suplemented by Oil.

The way our system is set up is that when the temp in the top sensor reaches the thermostat switch-on temp the oil kicks in (usually set to 40C) , and when it reaches the thermostat switch off -temp (usually 50C) it turns off... in effect the system is always on but I can control this manually, so on bright\sunny days I can lower the thermostat switch-on temp so that the solar does all the work and the oil never kicks. I do this because otherwise,after a morning shower for example, the oil might kick if temp drops but this defeats the purpose of solar espcially on a bright\sunny day.

I have no idea if this is a typical (or effective) set up and as our plumber was not great at explaining how to best manage the system I am looking for advice.

I noted in the resol manual that there is a setting which will allow me to activate the thermostat function for a certain time spans (t1 E, t2 E....t1 A, t2A) so to me it makes sense to block the thermostat function (ie. the oil kicking in if I understand correctly) for most of the time and to only have it active in the morning (to ensure hot water for showers) and in the evenings (for baths, kitchen etc).

I am not sure what the best settings would be around this to ensure we have enough hot water (for 2 adults + 3 kids under 7) and to maximse use of our solar.

Any thought, comments, advice appreciated.

freddyuk

If you set you immersion to come on via timer for 20 - 30 minutes in the mornings (summertime) you will always have enough hot water for showers etc. If the cylinder from previous days solar is hot enough then it will not come on as the immersion thermostat will not activate. You can calculate the cost of this very easily. If the immersion needs to come on for part of the 30 minutes you have set on the time clock then it is heating preheated water so not costing as much as having no solar input.
You only have 20 tubes which is not a lot for 280 litre cylinder. An additional 20 tubes would be a worthwhile investment if you have the space.
I would not use oil in summer only winter when you are heating the house anyway.
Same rule applies - if you need hot water early in the morning then boiler can supply up to the thermostat setting on the cylinder (DHW) then solar kicks in rest of the day. Make sure you only heat the top of the cylinder for what you need with oil/immersion NOT the whole cylinder. If sunny do the washing etc. in the afternoon or as soon as sufficient in cylinder. Try and get enough boost in the afternoon to heat up for the morning. No point in leaving a solar system stagnating when you have washing to do. (BUT you need a hot fill machine - very important) Once you know what your system can do you can adjust themostats to suit your lifestyle and override heating source for a boost if required. With only a few tubes you should have a top loading system to heat the top of the cylinder first if your controller can do this.

dots03

freddyuk wrote: »

If you set you immersion to come on via timer for 20 - 30 minutes in the mornings (summertime) you will always have enough hot water for showers etc. If the cylinder from previous days solar is hot enough then it will not come on as the immersion thermostat will not activate. You can calculate the cost of this very easily. If the immersion needs to come on for part of the 30 minutes you have set on the time clock then it is heating preheated water so not costing as much as having no solar input.
You only have 20 tubes which is not a lot for 280 litre cylinder. An additional 20 tubes would be a worthwhile investment if you have the space.
I would not use oil in summer only winter when you are heating the house anyway.
Same rule applies - if you need hot water early in the morning then boiler can supply up to the thermostat setting on the cylinder (DHW) then solar kicks in rest of the day. Make sure you only heat the top of the cylinder for what you need with oil/immersion NOT the whole cylinder. If sunny do the washing etc. in the afternoon or as soon as sufficient in cylinder. Try and get enough boost in the afternoon to heat up for the morning. No point in leaving a solar system stagnating when you have washing to do. (BUT you need a hot fill machine - very important) Once you know what your system can do you can adjust themostats to suit your lifestyle and override heating source for a boost if required. With only a few tubes you should have a top loading system to heat the top of the cylinder first if your controller can do this.

appreciate the feedback freddyuk.

Unfortunately we don't have an immersion (long story, it had to be removed due to problems) and can't manually or through a timer turn the boiler on\off...we only have two channels for the boiler which have been set up for 1)Upstairs + 2)Downstairs rads instead of all 1)rads + 2)hot water.

The only way we have any control over our boiler turning on\off is via the Resol panel (by changing the thermostat on\off temps).

The top of the cylinder is heated first and our 20 tubes seem to be pretty effective at this..at least on bright day. With the thermostat ON temp way down (to prevent the boiler kicking in) we have piping hot water from the solar alone.

The challenge is that if the next day is not bright and the solar has not been able to heat the tank, the boiler won't kick in as I lowered the thermostat ON temp previously to avail of solar...so I am not managing the system very effectively.

I will experiment with the thermostat switch on\off function to see if I can find a good time span for it to be active in all types of weather.

PeteHeat

My first thoughts were 20 tubes into a 280 litre cylinder suggests the solar array may not be large enough to bring the cylinder up to full working temperature however it will work as a good pre-heat system.

In modern or updated systems we would use a three channel programmer for the central heating / oil boiler, 1) Downstairs Rads, 2) Upstairs Rads, 3) Cylinder, all of the above zones are then controlled by both thermostats and the timer built into the programmer.

I would not be using the Solar controller to call on the oil boiler, our summer weather is so unpredictable it could result in the oil boiler bringing the cylinder up to temperature on a cloudy summers morning leaving the solar with very little if any work to do in our often sunny afternoons.

Using both programmers as described would give you better control because at worst all you need to do is press boost for hot water from the oil boiler, the other two (radiator circuits) do not have to come on at all.

As part of your upgrade you could do this in affordable stages:

1) Fit thermostatic radiator valves as these will prevent the radiators from heating on the warm mornings allowing all heat from the oil boiler to go to the cylinder.

2) Upgrade your heating programmer to three channel similar to This One also available in wireless etc.

3) If needed extend the solar array as the demand for hot water increases.

I hope the above is of some help.
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