I recently connected a Tuya 16A Smart Switch with temperature and humidity sensor to my 150L kwikot geyser (1.5kw PTC element) which is situated in my roof and is covered by a geyser blanket.  The sensor is taped against the nut of the PTC element.  

I have find that after heating the water (to 55⁰C) the temperature drops by 20⁰C within 2 hours and then cools off more slowly thereafter.

This seems excessive given that a geyser blanket is in place.

What is the expected temperature loss of a geyser?

Is the placement of the sensor possibly resulting in quicker temperature drop than inside the geyser?

 

 

You are measuring the element temperature more than the water temperature. What you are seeing there is the heat transfer from the element to the water.

Rather measure on the outflow pipe, as close as possible to the geyser wall.

My Kwikot 150L (without geyser blanket) loses ~0.5°C per hour at 55°C.

25 minutes ago, JustinSchoeman said:

You are measuring the element temperature more than the water temperature. What you are seeing there is the heat transfer from the element to the water.

Rather measure on the outflow pipe, as close as possible to the geyser wall.

My Kwikot 150L (without geyser blanket) loses ~0.5°C per hour at 55°C.

Same geyser and I get about the same heat loss during the night time. This is directly related to the ambient temp. During the day time the loss is far lower due to high roof temp. 

1 hour ago, JustinSchoeman said:

You are measuring the element temperature more than the water temperature. What you are seeing there is the heat transfer from the element to the water.

Rather measure on the outflow pipe, as close as possible to the geyser wall.

My Kwikot 150L (without geyser blanket) loses ~0.5°C per hour at 55°C.

That makes sense.  I will move the sensor and monitor again

13 hours ago, Erhard Wolf said:

What is the expected temperature loss of a geyser?

Calculating heat loss from a geyser involves considering factors such as the insulation of the tank, the temperature difference between the water inside the tank and the surrounding environment, and the surface area of the tank.

Here's a simplified formula for estimating heat loss:

Q = U * A * ΔT

Where:

Q is the heat loss in watts (W).

U is the overall heat transfer coefficient, which depends on the insulation and construction of the geyser's tank.

A is the surface area of the geyser tank in square meters (m²).

ΔT is the temperature difference between the water inside the tank and the surrounding environment in degrees Celsius (°C).

You can find U and A from the geyser's specifications or at least try and get the specs from manufacturer or by measuring the dimensions of the tank. The temperature difference ΔT can be the difference between the set point temperature (the desired water temperature) and the ambient temperature.

Link below report(pdf) on study done on water heater efficiency in South Africa interesting facts.

https://www.savingenergy.org.za/wp-content/uploads/2019/05/Report_GeyserStudy_Final-Report-27-November-2014.pdf

After experimenting a bit, I found that one geyser blanket is not enough, I have three blankets as well as insulation (think it is R1) around the hot water pipes coming out of the geyser over several meters.

7 hours ago, HendrikBigChief said:

After experimenting a bit, I found that one geyser blanket is not enough, I have three blankets as well as insulation (think it is R1) around the hot water pipes coming out of the geyser over several meters.

Insulating the geyser pipes is another important factor to consider and do - not just adding a geyser blanket.

I had to replace the insulation for my geyser outlet pipe recently as the sun had eaten away at it.

19 minutes ago, PsyCLown said:

Insulating the geyser pipes is another important factor to consider and do - not just adding a geyser blanket.

I had to replace the insulation for my geyser outlet pipe recently as the sun had eaten away at it.

When using water the outlet pipe will make a sizeable difference but the heat loss while no water is used the effect I think will be small. This is what I see as heat loss. 

2 hours ago, Scorp007 said:

When using water the outlet pipe will make a sizeable difference

Especially on longer hot water pipes where you wait 30 to 40 seconds for water to heat up at the faucet.

On 2023/09/03 at 7:05 PM, Erhard Wolf said:

That makes sense.  I will move the sensor and monitor again.

I have moved the temperature/ humidity sensor to the outlet pipe as it leaves the geyser, and what a difference it makes.

Now I am measuring water temperature as we use it.

I already have a 50mm green wool geyser blanket but have covered this with a kwikot silver geyser blanket as well.  I have also insulated water pipes too and from the geyser as well as the sensor on the pipe.

Now I have minimal heatloss (about 0.7C/hour)

Thanks for the advice