Average temperature loss in hot water tank overnight.

I've noticed that the hot water temperature is dropping by 10 degrees C overnight. I normally have the heating on 6-8:30pm which heats the water. The temperature of the tank is >45C afterwards. The tank is a 300Litre tank in a new build. I've started checking the temperature in the morning ~8am and the temperature is closer to 35C. This temperature drop is excessive. I would have thought the temperature loss would be minimal, 1 to 2 degrees C. What sort of temperature losses are others seeing? Any ideas as to why the temperature could be dropping by so much?

Losing heat through the (exposed) connecting pipes to the tank?

Depends on the type of tank and it's levels of insulation. Hot water use in the evening without the boiler on will also reduce your cylinder temp. You may also be getting a little parasitic circulation between the uninsulated connecting pipework which may lead to water temperature drop.
Note: your hot water should be stored at a temperature of at least 60 degrees to stop the possibility of legionella bacteria growth.

villa 1 said:

Note: your hot water should be stored at a temperature of at least 60 degrees to stop the possibility of legionella bacteria growth.

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100%

if your cylinder stat is set to 45 deg id change it immediately.

checking the temp at 8:30 might be inaccurate if this hot water is used past this time. Then the cylider will refill with cold water which would have a significant effect of the temp drop.

try setting the boiler to heat the water as late as possible, so nobody uses any, one night... and check it the following morning first thing... then see what the temp drop is.

Assuming you have solar heating (which, with a 300 litre cylinder seems safe) the temp drop may also be caused by cycling of the solar system actually draining heat from the cylinder. im not a plumber so perhaps those with better knowledge might theorise how this could happen... perhaps the solar system is still pumping at night??

Ensure that you heat your domestic tank to 60c atleast once a week.

Don't heat your water in the evening if you don't require it. If you need it early in the morning, set your timer.

As already stated, any time a hot outlet is used, cold water is introduced into the cylinder, hence dropping overall temperture.

Thanks for the replys.

1. The pipes in and out of the tank are exposed. I'm going to get insulation cladding for them.

2. The tank is situated on the ground floor. Do you think its worth sealing the door to prevent draughts/cold air entering the room. The hotpress is located close to an external wall vent which means that area of the house
would be a little colder than the rest.

3. I do have solar panels. Is there an experiment i can do to see if the panels are somehow circulating cold water into the tank during the night?

4. The 10 degrees C of temp drop was without any hot water usage in the house during the night. This represents almost 1 degree C of temp loss every hour. Has anyone else looked at the temp loss on their tank overnight for comparison?

What type of solar system do you have ? Any brand names on the cylinder or the system ? Some twin coil cylinders arrived here from China with very poor insulation, some solar systems are filled with water instead of glycol and the controller is set to circulate the water through the panels at night when the temperature drops to protect the solar panels / tubes from freezing.

I'm having exactly the same problem in Moraira. I have a 200 litre Vitrex (Zaragoza) tank with 2" thick foam rubber lagging under a cylindrical flexible jacket. This is a very old and simple system, with what look like old radiators on the roof (no glass tubes etc). I can´t get the grundfoss pump to work by turning the cylinder stat down ( to call for the warmer water from the roof). The water yesterday afternoon was 80 degrees, we took one brief shower last night, and this morning it is down to 20 degrees and not rising even at 11 am and a sunny day. hmmm.

Guys, its cold [max 12 degrees in the day] and we had very "watery" sunshine yesterday due to cloud cover, with a clear night and zero degrees last night in places.

It might be April on the calander, but its only a warm February day in Real Life.

ONQ.

Just a few thoughts on this.

1) Is the the temperature drop at the top, or the bottom of the cylinder? Usually there are two probes in the cylinder. If there was recirculation going back up to the panel at night (because of a faulty one-way valve, or because the controller is running the pump in anti-freeze mode) then it should only affect the bottom of the cylinder.

2) Is any part of the hotpress, or its surrounding pipework warm? I have often seen systems where the solar circuit was properly insulated, but the pipes on the boiler coil aren't insulated at all, and there is substantial heat loss here.

There can be heat loss from each fitting on the cylinder not being over-insulated. Best practice is to get a length of 1.5" armaflex, and put it OVER the other insulation and butted up to the cyliner to totally insulated the fittings on the cylinder.

3) I am assuming that the system is unvented, but if not, is the vent pipe from the top of the cylinder going up to the loft, and if so, is it warm? This pipe should go horizontally for about 50cm before rising to prevent this heat loss.

By the way, in some parts of the country (such as West Cork), it is fine to use the controller as an anti-freeze device provided you are using vacuum tubes. The amount of lost heat is negligible in this situation, and it is usually lost only from the bottom of the cylinder where the solar coil is located.

Solar heating should be working very well this last week. The levels of light are great and a roof angle of 45 degrees is optimal at this time of year. The air temperature should make only a very slight difference, even for flatplates. If your system isn't working properly now, something is wrong.

I have just come back from West Cork where there is a newly built house which as extended family we get to use and it has solar heating system. It is a large dormer house with the most fantastic water system.....large nearly floor to ceiling tank and filtration system in the utility room. However, the house wasn't used since before Christmas and while the water was hot....because of the beautiful sunshine we had.....I still used the heating to boost the water temperature up before use! By the time we left at the weekend the water was good and hot. I live in Galway myself and have thought of putting in these solar panels in my own dormer. My house is 12 years old on a south facing site but would the cost be worth it? It is a 2,500 sq. ft. house and by and large as there are only 2 of us in the house would it justify the expense?

I say this each time I come back from West Cork......

Mopsy said:

I live in Galway myself and have thought of putting in these solar panels in my own dormer. My house is 12 years old on a south facing site but would the cost be worth it? It is a 2,500 sq. ft. house and by and large as there are only 2 of us in the house would it justify the expense?

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Regardless of house size, for two people, you only need a modest system. You could put a 40 tube/200L system in for in or around €4,500 which after the grant would be about €3500.

There was something wrong with the system you were using in the holiday home. I worry about solar panels on holiday homes unless there is a heat dump present. Very few houses have such a heat dump, but if the heat dump is set up incorrectly, it may have caused the problems you experienced. But in an unused house, the cylinder should be at 60 degrees no problem.

The system for your own house would depend on the number of occupants, and hot water use. Lots of questions, like do you use showers or baths? Is the house occupied during the day (needing more heat, but less storage than a house only occupied at night), is the roof roughly south facing? Is there a long run from the location of the panel to the cylinder? Do you have a preference for tubes or flatplate? Do you like to peel your potatoes in warm water????

Some houses use very little hot water - everything done in a dishwasher, occasional frugal showers etc., in which case there is lower hanging fruit than a solar water heater, but otherwise, it should stack.

During the winter, your central heating provides quite cheap hot water. Usually in summer time, the heating is off, and you are heating the cylinder, either with an immersion or by using the central heating system, heating a boiler, flue, pipes etc., just to heat a small cylinder. Both are very inefficient and push up the cost of summertime hot water.

Also, usually a solar installation incudes replacing your cylinder, usually with a more efficient one. That will give you some savings during the winter as well.

Lastly, isn't it just nice to have your hot water coming from the light, instead of some oil well?

quentingargan said:

Regardless of house size, for two people, you only need a modest system. You could put a 40 tube/200L system in for in or around €4,500 which after the grant would be about €3500.

There was something wrong with the system you were using in the holiday home. I worry about solar panels on holiday homes unless there is a heat dump present. Very few houses have such a heat dump, but if the heat dump is set up incorrectly, it may have caused the problems you experienced. But in an unused house, the cylinder should be at 60 degrees no problem.

The system for your own house would depend on the number of occupants, and hot water use. Lots of questions, like do you use showers or baths? Is the house occupied during the day (needing more heat, but less storage than a house only occupied at night), is the roof roughly south facing? Is there a long run from the location of the panel to the cylinder? Do you have a preference for tubes or flatplate? Do you like to peel your potatoes in warm water????

Some houses use very little hot water - everything done in a dishwasher, occasional frugal showers etc., in which case there is lower hanging fruit than a solar water heater, but otherwise, it should stack.

During the winter, your central heating provides quite cheap hot water. Usually in summer time, the heating is off, and you are heating the cylinder, either with an immersion or by using the central heating system, heating a boiler, flue, pipes etc., just to heat a small cylinder. Both are very inefficient and push up the cost of summertime hot water.

Also, usually a solar installation incudes replacing your cylinder, usually with a more efficient one. That will give you some savings during the winter as well.

Lastly, isn't it just nice to have your hot water coming from the light, instead of some oil well?

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Thank you very much for taking time to give me such a detailed response.

Regarding the family holiday home, I would guess the water was just at 60 degrees but I still used the heating to boost it. The OFCH is set up with three buttons, one for downstairs heating, one for upstairs and one for water. I will be going there again next month and will check out this heat dump.

Regarding my own house. Since I lost my job at Christmas, by and large I am in the house during the day while OH is working. Other than visiting family about twice a month which boosts family number to 5, it is mainly myself and OH in the house. The front of the house is south facing while the hot press is to the rear of the house, upstairs. I am not bothered about tubes or flat panel. We have a Triton T70 electric shower in the en-suite while downstairs is a gravity fed shower from the tank. Good hot water when central heating (oil) is on. Yes, you are right, I use the immersion during the summer, but I would be conscious about water usage and heating it. By and large, showers and not very long ones, every second day. Never use the bath...in fact we never use the bathroom! I am trying to judge how long a run there would be from the south facing run to the cylinder and I am guessing it would not be too long!

Are the grants still available in these recessionary times? I have a friend who is building on an extension in an upstairs large apartment at the moment and has a guy installing these solar panels at a cost of €3,500. I know he is not registered but by and large knows his stuff. All the same I would not be tempted and would prefer some kind of registered guy.

I suppose I still think that it would be nice to have the water heated from the outside. Other than the panels on the roof, what internal work has to be done and how intrusive and disruptive is it? I realise that tank in hot press has to be replaced. Is the tank in the attic made redundant?

Thanks in advance for any tips!

villa 1 said:

Note: your hot water should be stored at a temperature of at least 60 degrees to stop the possibility of legionella bacteria growth.

Click to expand...

Gaw'd I just got a tank stat and zone valve fitted last year so I could lower the heat in the tank down to around 40'c as 60'c is way to hot and burns the hands of me and so wasteful.

How does this legionella affect things as I thought it was only a problem if it got into the mains water.

villa 1 said:

Depends on the type of tank and it's levels of insulation. Hot water use in the evening without the boiler on will also reduce your cylinder temp. You may also be getting a little parasitic circulation between the uninsulated connecting pipework which may lead to water temperature drop.
Note: your hot water should be stored at a temperature of at least 60 degrees to stop the possibility of legionella bacteria growth.

Click to expand...

Surely legionella won't get a start in an enclosed system and secondly because of the turn over in the water system?


Most people do not want 60+ degrees of heat. Agree that stagnant water in a shower head is more dangerous from a legionella perspective and especially as a mist will be generated by the shower. 40 degrees should be okay for the wash basin and general washing use?

Mopsy said:

Are the grants still available in these recessionary times? I have a friend who is building on an extension in an upstairs large apartment at the moment and has a guy installing these solar panels at a cost of €3,500. I know he is not registered but by and large knows his stuff. All the same I would not be tempted and would prefer some kind of registered guy.
.....Other than the panels on the roof, what internal work has to be done and how intrusive and disruptive is it? I realise that tank in hot press has to be replaced. Is the tank in the attic made redundant?

Click to expand...

Yes, the grants are still available, and besides giving you some dosh towards your costs, they also set standards in the trade.

The only reason for an installer not to be registered is because they haven't got around to doing the training, or they are using uncertificated panels. I'm not normally into petty regulation, but there are aspects of the training that I think are worthwhile and should be done by all installers as solar water heating is a new system to most of us.

If you have an attic tank (vented system) you can usually leave that in place, but if you want to change to an unvented system, since you are changing the cylinder, it isn't expensive to upgrade to an unvented system provided the pipework in the house is up for that!

Usually the most disruptive part of installing a solar heating system is changing the cylinder. Besides this, there are two pipes (often a twin-bore flexible insulated pipe) that go from here to the loft. In addition, there is a pumpstation, expansion vessel, electronic controller, and there ideally should be some sort of heat dump, often a radiator in the bathroom or in the loft. The whole thing takes about two to two and a half days, but one of those days in full is mounting the panel outside.

If you are putting a flatplate into the roof, there is also a bit more mucking about taking out slates etc., but still all done within 3 days.

Fiskar said:

Surely legionella won't get a start in an enclosed system and secondly because of the turn over in the water system?

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There are low concentrations of legionella in a lot of the mains water - it only does harm if it gets a chance to breed, which can happen rapidly at temperatures of 25 to 40 degrees. Although 55 degrees does knock back the population, the regulations suggest 60 degrees. The idea is that a €60 blending valve on the outlet from the cylinder brings the temperature back down to one that is comfortable and safe for the taps - especially for children who scald easily.

OK I am going to look into this method of heating the water. If I do have these panels installed, would I have to change the Triton T70 electric shower in the en-suite, that is, if I make the tank in the attic redundant? or can it be kept, of course, if the tank in the attic stays in place or does this complicate the system?
The other shower in the house is in a downstairs bedroom, which is gravity fed.

I must now try and source a suitable installer in the Co. Galway area or surrounding counties, like Offaly or Tipperary.

jryan said:

Thanks for the replys.

3. I do have solar panels. Is there an experiment i can do to see if the panels are somehow circulating cold water into the tank during the night?

Click to expand...

There should be a HP option on your control panel for the solar panels - usually located close to the hot water tank - this is the panel you will see the tank temp - press the left or right arrow buttons (or similar depending on the control panel) until you get to a HP screen - record the hours pumped (HP) at sun down and get up before sun rise and see has the HP changed - the pump will pump (if setup correctly) if the panels are 5 - 10 degrees warmer than the tank, therefore they should not be pumping at night when the panels are cooler than the tank.

As Quentin says the regulations insist on +60 degree storage temperature for hot water (re, hospitals, nursing homes etc). This stored, sometimes stagnant hot water can breed legionella bacteria especially on long pipe runs where the temperature can drop to growth temperatures.
The solution is to store your hot water above 60 degrees and then install a mixing/blending valve on the secondary flow hot water that exits the cylinder. This will overcome scalding problems etc. It is a good idea to send a seperate hot water supply to your kitchen/utility unmixed for hot water washing. This hot supply is taken off before the mixing valve.
The installation of this mixing valve will also negate the need to fit costly thermosatic shower mixing valves in bathrooms, ensuites etc.