Is this a normal heat loss graph from an UVC?

[Thorfun]

as per the title. yesterday I got the hot water in our tank up to 48°C-ish. over the next 21hrs it dropped approx. 10°C. 

 

to me that sounds pretty good but just wondering what others thought or what other UVCs lose?

 

 

it's a Mitsubishi pre plumbed Ecodan UVC 300l

[SteamyTea]

Depends how much you used and when.

10⁰C drop seems quite a lot to me when the starting temperature is only 48⁰C.

I have posted up my cylinder temperatures on other threads. No idea where though.

[JohnMo]

Also does it depend where the measurements is taken.  As I understand it - the top of the cylinder should stay at a given temp, until the thermocline (not sure if that's the correct word now) slowly moves up the cylinder over time as heat is lost. So a full cylinder of 48 deg water starts at that temp all way top to bottom, as heat is lost the bottom of the cylinder moves closer to ambient, the ambient temp creeps up the cylinder until the whole cylinder is at ambient.

[Alan Ambrose]

0.5C per hour? Assuming no one has used the hot water? I'm not sure that's great actually - I'm getting about that for a badly insulated thing from 30-years ago. Interesting data though.

 

In a real-life case,  I wonder how much is heat loss and how much is just mixing with the incoming cold water.

 

Actually I'm interested if anyone else has data - as I had on my to do list to replace the cylinder here with something more modern with 'better insulation'. 

Edited June 13, 2023 by Alan Ambrose

[ProDave]

Where is the temperature probe?  i.e. how far up the cylinder.

 

Where is the probe that the heat pump uses?

[MJNewton]

3 hours ago, Thorfun said:

as per the title. yesterday I got the hot water in our tank up to 48°C-ish. over the next 21hrs it dropped approx. 10°C. 

 

to me that sounds pretty good but just wondering what others thought or what other UVCs lose?

 

Sounds reasonable.

 

Our 150L Range Tribune UVC (fairly run of the mill I think? 15 years old now though) has a purported standing heat loss of 1.31 kWh/24hrs (no stored/ambient temperatures stated - is this standardised?¹) so converting that into °C heat loss:

Convert from Watts to Joules: 1.31 kWh x 3.6 MJ/kWh = 4.716 MJ
Convert to °C based on the heat capacity of the specified quantity of water: 4.716 MJ * 1000000 / (150000 mL x 4.2 J/ml) = 7.5 °C

 

Given the variability of installation the published figure might well only include the cylinder itself and not any connected pipework thus it would lose more in real life. Stratification may also lead to slightly different results depending on where the probe is too I think.

 

¹ Edit: Yes, it looks like the various related British Standards specify a stored water temperature of 70°C and an ambient room temperature of 20°C for standing heat loss measurements. Thus, your 48°C starting point may or may not have more significance than I have given consideration for.

Edited June 13, 2023 by MJNewton

[Thorfun]

2 hours ago, SteamyTea said:

Depends how much you used and when.

10⁰C drop seems quite a lot to me when the starting temperature is only 48⁰C.

I have posted up my cylinder temperatures on other threads. No idea where though.

not used any. not got any taps or anything fitted. just got the tank temp to 48°C and turned ASHP off as an experiment!

 

2 hours ago, JohnMo said:

Also does it depend where the measurements is taken.  As I understand it - the top of the cylinder should stay at a given temp, until the thermocline (not sure if that's the correct word now) slowly moves up the cylinder over time as heat is lost. So a full cylinder of 48 deg water starts at that temp all way top to bottom, as heat is lost the bottom of the cylinder moves closer to ambient, the ambient temp creeps up the cylinder until the whole cylinder is at ambient.

not got a clue where it's taken tbh. the data is from the Mitsubishi FT6 controller.

 

48 minutes ago, ProDave said:

Where is the temperature probe?  i.e. how far up the cylinder.

 

Where is the probe that the heat pump uses?

don't know and don't know! sorry. 😞 

[Thorfun]

actually, the tank is connected to our DHW manifold but it goes no further. the pipes connecting to said manifold are not currently lagged (they will be but it's a work in progress) so I guess some heat loss could be out of the water sitting in those copper pipes?

[SteamyTea]

Here is what happened inside my cylinder between 17/02/2021 and 01/01/2022.

My upper cylinder probe was just taped to the top of the cylinder, so under reads a bit.

Mean temperature over a typical day was 43.1°C, max was 45.1°C and min 40.5°C, so a range of 4.6°C with normal usage.

Just had a quick look at the main data (30 second sample rate), the base of the cylinder had a mean of 25.1°C, a min of 11°C and a max of 53.7°C.

The top of the cylinder had the same min and max as the base, so I must have been away for a few days and let it cool completely.

The loft tank than supplies it had a mean of 15.1°C, min of 8.3°C and a max of 27.3°C.

 

Edited June 13, 2023 by SteamyTea

[Thorfun]

7 minutes ago, SteamyTea said:

Here is what happened inside my cylinder between 17/02/2021 and 01/01/2022.

My upper cylinder probe was just taped to the top of the cylinder, so under reads a bit.

Mean temperature over a typical day was 43.1°C, max was 45.1°C and min 40.5°C, so a range of 4.6°C with normal usage.

 

so that heats at 1am and then tops up during the day with minimal energy input?

 

I guess I need to heat the water and then see the energy usage to maintain it at 48°C during the day/night. I might give that a go tomorrow.

[SteamyTea]

Just now, Thorfun said:

so that heats at 1am and then tops up during the day with minimal energy input?

Yes it did then.

The tops are very occasional times when I was doing two jobs and was bathing 3 times a day, and E7 can be switched on briefly for gird balancing, but not so much these days, if at all.  The chart shows hourly mean.

My energy plot is for the whole house though.

3 minutes ago, Thorfun said:

I guess I need to heat the water and then see the energy usage to maintain it at 48°C during the day/night. I might give that a go tomorrow.

It is a worth while exercise.

I stopped monitoring because I was not learning any more about my water energy usage, using less in he winter saves me more.

Last year and so far this year, I have cut my usage by 40 lt a day (we are in serious draught down here). As 2/3^rd of that is hot water, there is an energy saving of around 0.6 kWh/day.