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Best temperature to heat a geyser up to, for least amount of heat loss


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I have set mine to 70 degrees ( max on the thermostat ), use inverter/pv during the day,so as to use the least amount of grid, with winter would it be better to set geyser at a lower temperature for the least amount of heat loss, geyser is in the attic with a blanket.

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5 minutes ago, Shadders said:

It would but you don't want to drop it too low that bacterial count becomes an issue. Australia limits the minimum temperature to 65 degrees if memory serves correctly. This might be of interest as well:


https://powertime.co.za/online/how-to-save-electricity-geyser/

Well I call BS on point 2. I have the data and savings to prove it worked in my case. Anyway, don't want to derail the thread.

I use a geyserwise and heat the water to the required temp that I only need hot water in the shower. Call it 44 degrees in the morning for me, 50 in the evening for the wife and kid. Sunday I pump it up to kill the bugs. This is the advantage of the geyserwise over a timer, you can set different temperaturea at different times of the day. 

 

My objective is to decrease consumption, not utilize excess pv. Different objectives will result in different solutions. 

 

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2 minutes ago, Craigm said:

Well I call BS on point 2. I have the data and savings to prove it worked in my case.

Lol I agree and it's nice to have confirmation. I guess they didn't take into consideration use case scenarios.

I did not know geyserwise had the option of various heating cycles, very useful and could easily be tweaked to maximise PV excess.

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Posted (edited)

@Craigm, my aim was to utilize pv to heat the geyser ( instead of grid ) I use a timer to limit the heater only switching on when there is reasonable pv during the day, and therefore set the thermostat to the maximum of 70. with winter, solar production is decreasing, so more grid is being used, my thinking is set the temperature lower and use the grid to re-heat( boost the temperature ) the water in the evening/early morning, as i have sometimes use 10 kwh from the grid on a bad solar day

Edited by Tariq
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9 minutes ago, Tariq said:

@Craigm, my aim was to utilize pv to heat the geyser ( instead of grid ) I use a timer to limit the heater only switching on when there is reasonable pv during the day, and therefore set the thermostat to the maximum of 70. with winter, solar production is decreasing, so more grid is being used, my thinking is set the tempreture lower and use the grid to re-heat( boost the temperature ) the water in the evening, as i have sometimes use 10 kwh from the grid on a bad solar day

I agree with the logic of heating the water just before you're going to use it. So if you know you're going to be using the grid to boost the temp, I think your logic is sound. 

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Posted (edited)
28 minutes ago, Shadders said:

I did not know geyserwise had the option of various heating cycles, very useful and could easily be tweaked to maximise PV excess.

Here is a picture from the TSE manual. The old models didn't have this (my dad's TSE doesn't have this) but the two units that I bought over the last 2 years work like this. 

IMG_20210526_123521.jpg

GW.PNG

Edited by Craigm
Added weekend setup
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Yes agree with Craigm. Older Geyserwise units don't have option to set different temperatures for different blocks. 

Means that it a good idea to weekly manual intervention for an anti-legionella temperature increase of geyser to  70 °Celsius.

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2 hours ago, Tariq said:

@Craigm, my aim was to utilize pv to heat the geyser ( instead of grid ) I use a timer to limit the heater only switching on when there is reasonable pv during the day, and therefore set the thermostat to the maximum of 70. with winter, solar production is decreasing, so more grid is being used, my thinking is set the temperature lower and use the grid to re-heat( boost the temperature ) the water in the evening/early morning, as i have sometimes use 10 kwh from the grid on a bad solar day

I have done that. Use the PV to heat the geyser. In winter or rainy summer days the hybrid inverter just combine whatever pv is available with the grid power.

Actually added a second geyser to have enough hot water not to have to reheat during non pv hours.

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2 hours ago, Shadders said:

Lol I agree and it's nice to have confirmation. I guess they didn't take into consideration use case scenarios.

Geyser timers are controversial.  Also done loads of testing.

Best use case is if you heat the water before use and then use it all and let the geyser stand with cold water.  I could get that up to 1.5-2kWh saving on an average 10kWh daily use. In practice we never use the geyser like that and the saving is normally below 1kWh or 10%.

 

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3 minutes ago, Tariq said:

Hi @Pietpower, how is the second geyser hooked up, is it in series, does it have an element, if so, is it powered by the inverter

It is in series.  Only one element in the second geyser.  At the moment I use a pump to circulate the water between the two and am wasting energy. Although funny enough my 10kWh average only went up to 12-13kWh with the second geyser added.  You pay for the water used and heat loss and not the total volume stored.

In the future the first geyser will have a flat panel collector to "pre-heat" the water and then the second geyser will bring the water to a higher temperature.  A higher temperature is effectively a bigger storage volume.  But the second geyser will start with hot water so hopefully my original 10kWh will be much lower with added hot water volume stored.

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Another thing I wish I knew up front:  Insulating my ceiling had a negative effect on the hot water energy.

With insulation on top of the ceiling and water pipes above that on the trusses the heat from the house is isolated from the pipes.  In winter my cold water is now colder and hot water also have a high heat loss flowing through the pipes (and that is with insulated pipes)

I can't believe how big a difference it makes and it becomes very obvious when you take a shower in the morning vs the afternoon when the ceiling void is warmer.

Next time I will try and run the insulated pipes direct on the ceiling underneath the trusses and insulation.

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Heat loss is directly proportional to temperature difference. The hotter your geyser, the more you lose to the environment. Ideally you want it to be just hot enough to prevent cold showers - but that is hard to predict and achieve so we all have to have a bit of leeway on our temps. 

My current strategy is to heat to a minimum temp during peak solar periods to get me through the evening showers. This varies with season, 52°C in summer, 55°C in winter. If battery is full and solar is available, I allow it to heat all the way to 70°C to not waste solar power. This generally happens more than once a weak to ensure I get the 55°C minimum for an hour to stop Legionnaires Disease.

As a backup I monitor geyser temp and if it drops below 40°C at any point I could need water (Before 8pm in the evenings or before our domestic comes on Tuesdays and Thursdays) I'll use the grid to heat back up to 45°C. I also then have modes for when guests are in the house to increase all these temp set points to ensure we don't run out of water.

Having home assistant and a bunch of monitoring opens up a lot of options!

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Hi, Reading with interest, I bought my first solar PV geyserwise system about 3 three years ago, The early days they gave lots of problems on the MPPT, Just to explain the kit, Its PV panals to a MPPT to a Element they supply with 2kw AC and 900w DC in the same element.All this controlled by the Geyserwise controller A year ago I bought the 2nd Kit (have 2 Geysers) Many pro for and few against  going this VS The solar Tubes. Winter temp set to 55 and its very hot, Summer set to 45 and its very hot (red skin) Have to change your habits a bit and shower / Bath reducing the water temp  and let the sun catch back up to temp (Morning mostly),if by 5pm you have cold water its  back to Eskom. But that goes for all the Sun heated systems. I have this month Bought the Sunsynk after learning the benifits of PV on the Geysers and of course the Eskom Saga is a must to have another a solar system.

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On 2021/05/26 at 3:06 PM, Pietpower said:

It is in series.  Only one element in the second geyser.

I have a 200ltr high pressure EV tube geyser on roof and my old spare 150ltr kwikhot in attic, the kwikhot was switched off for about three years now as it is just waiting as a backup. Three weeks back I realized the EV tube geyser’s electric element has a problem when the temp stuck at 44 late afternoon after my son had showered and the element did not switch on anymore, we sometimes heat the water with eskom when needed. I realized something must be wrong with the element but not feeling to go on the high pitched roof I rather opened the water to my spare geyser in the attic and switched it on to see what happened. These to geysers are in parallel over each other. Within about two hours there were hot enough water for showers.

On a average day the EV heats to about >67 and with the kwikhot geyser set to 60 with Eskom power these two geyser seem to compliment each other very well. I realized in the evenings after showers there is a much smaller dip to about 50 degrees on the EV tube geyser where before it would fall to 30’s. I am now also considering to fit a flat plate on the attic geyser to do away with Eskom completely.

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BActerial issue  is way overstated - I set my thermostat to comfortable showeer  temp - 43-44 deg. Showerdirect , no added cold wate r. Have done so for 20 year sand never had any bacteria infection

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Question- does have two geysers 

On 2021/05/26 at 3:06 PM, Pietpower said:

It is in series.  Only one element in the second geyser.  At the moment I use a pump to circulate the water between the two and am wasting energy. Although funny enough my 10kWh average only went up to 12-13kWh with the second geyser added.  You pay for the water used and heat loss and not the total volume stored.

In the future the first geyser will have a flat panel collector to "pre-heat" the water and then the second geyser will bring the water to a higher temperature.  A higher temperature is effectively a bigger storage volume.  But the second geyser will start with hot water so hopefully my original 10kWh will be much lower with added hot water volume stored.

Does having two geysers in series reduce the water pressure in by any chance?

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2 hours ago, NoordSolar said:

BActerial issue  is way overstated - I set my thermostat to comfortable showeer  temp - 43-44 deg. Showerdirect , no added cold wate r. Have done so for 20 year sand never had any bacteria infection

I listened to a talk of an expert in the field and was shocked at what he said.  In general you won't have an infection or link something specific to the water but just have a healthier life with healthy pipes.  He actually feel that water pipes should be cleaned.

As for Legionnaires you are increasing your chances to get it but I think they will still remain slim.  You will need to maintain a low/moderate temp in the geyser for a long time without replenishing the water and then also create a mist like in a shower to get it into your lungs. 

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On 2021/06/01 at 12:42 PM, NoordSolar said:

BActerial issue  is way overstated - I set my thermostat to comfortable showeer  temp - 43-44 deg. Showerdirect , no added cold wate r. Have done so for 20 year sand never had any bacteria infection

I guess it also depends on the water quality in your area and the municipality that you live in. 
 

What you are saying is similar to someone that feels wearing a seatbelt is a waste of time. They haven’t worn a seat belt for 20 years and they are still alive so don’t see the need for it even though it can save lives “in the event of certain types of accidents “

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Posted (edited)
On 2021/05/26 at 12:23 PM, Tariq said:

@Craigm, my aim was to utilize pv to heat the geyser ( instead of grid ) I use a timer to limit the heater only switching on when there is reasonable pv during the day, and therefore set the thermostat to the maximum of 70. with winter, solar production is decreasing, so more grid is being used, my thinking is set the temperature lower and use the grid to re-heat( boost the temperature ) the water in the evening/early morning, as i have sometimes use 10 kwh from the grid on a bad solar day

 

As a better alternative to a timer, have you checked if your inverter/charge controller has an "aux" or "dry contact" signal? It's basically a switch that turns on or off when a set battery voltage or state of charge has been reached. That way your heater would only use excess power after your batteries are fully charged.

Edited by tetrasection
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