which machine are you using

macaber8 wrote: How do you measure real group temperature after water hit the puck?

Not directly.

First, I fully opened the needle valve of my thermofilter so the flow rate was very high and the water temperature was affected by the grouphead least and got the result that the water temperature went down 4 degrees C from the coffee boiler to the grouphead.

Second, I dialed the needle valve to match the extraction flow rate. If the water temperature was higher than it in the first step, that meant the real grouphead temperature was higher than the water temperature in the first step. Then I tuned down the grouphead temperature and repeated the test and got the result that the real grouphead temperature was lower than it on the PID by 2 to 3 degrees C.

pizzaman383 wrote:My experience with my 3-PID double boiler lever shows that the best temperature stability and the most consistent shot temperatures come when the water hitting the group head is nearly the same temperature as the group head. This means that the water doesn't heat up the group head very much which means that the shot water temperature will have the minimum amount of variation.

Same here, and I like the taste most.

Were talking about different machines though with different groups and water delivery..

Even the nurri is different to the Evo and they share the same style group

bakafish wrote:Exactly on my Nurri Leva. ...When I lifted the lever, I turned off the machine to make sure the PID was not working ..., the water temperature went down to 9X degrees C quickly and kept there till the end, not declining.

Interesting.
So does that mean on your Nurri you won't have temperature declining profile during extraction, like on most level machines?

Not on the dual boilers unless you set them to do so.

The water doesn't interact with the steam boilers etc so there very temp stable.

You will how ever have the declining spring press with which ever spring is fitted.

I'm not sure how many pids the nurri has or it's configuration

Cuprajake wrote:Were talking about different machines though with different groups and water delivery..

Even the nurri is different to the Evo and they share the same style group

While that is true we were talking about water and group head temperature.

Machines that separately control both the group head and brew water temperature can be configured to match those emperatures regardless of how they are heated and regardless of the specifics of the lever group head.

jamesz wrote:Interesting.
So does that mean on your Nurri you won't have temperature declining profile during extraction, like on most level machines?

I don't know why but at least the temperature reading showed this. Maybe it relates to the weather and environment. I don't know other lever machines either. There are many group types and dipper, thermosyphon, etc. Not all of them were measured. Most people just accepted "the water temperature during extraction of a lever machine is declining".

First, I fully opened the needle valve of my thermofilter so the flow rate was very high and the water temperature was affected by the grouphead least and got the result that the water temperature went down 4 degrees C from the coffee boiler to the grouphead.

Second, I dialed the needle valve to match the extraction flow rate. If the water temperature was higher than it in the first step, that meant the real grouphead temperature was higher than the water temperature in the first step. Then I tuned down the grouphead temperature and repeated the test and got the result that the real grouphead temperature was lower than it on the PID by 2 to 3 degrees C.

I did some thinking about your test. The difference between the 2 tests is the flow rate. Assuming before the test, group temperature is 91C and Boiler Temp was 97.5C. For the heat transfer between water to the group head:
Heat transfer rate =Delta T/Thermal resistance
Delta T = Temperature difference between Boiler Water and Group
Thermal resistance is constance

When you flow water slower, water temperature difference entering and exiting the group head would be larger, because water has more time to give its heat away to the group. So averagely, the temperature of water in the group head at any moment is close to group temperature. Therefore, the temperature difference between water and group would be smaller initially. Heat transfer rate is smaller.

When you flow water faster, water temperature difference entering and exiting the group head would be smaller, because water has less time to give its heat away to the group. So averagely, the temperature of water in the group head at any moment is close to boiler temperature. Therefore, Temperature difference between water and group would be larger initially. Heat transfer rate is larger. This means, although water out of the group head has higher temperature, but water actually lose thermal energy quicker.

In this scenario, we don't have a cooler at the group, only a heater. When group temperature is increased, the only thing heater can do is to shut off and wait for group to cool down. Base on energy equivalence,
q_water_loss = q_group_gain+q_group_convection
q_group_convection is the heat exchange between the group and environment, this should be similar during faster or slower water flow rate.
When you flow water faster, q_water_loss is larger, this means q_group_gain is larger. This means, group gets more thermal energy. Since group has a constant thermal mass, the group temperature raise will be higher when the through water have higher flow rate..

With all that said, I quote you:

Second, I dialed the needle valve to match the extraction flow rate. If the water temperature was higher than it in the first step, that meant the real grouphead temperature was higher than the water temperature in the first step.

The water temperature should be lower comparing to the first test. The group temperature raise should be lower than the first test as well. If not, something else is heating the water. It shouldnt be the group PID, since the water temperature is already higher than group PID setpoint at this moment. The only thing I can guess is that the boiler keep transferring heat to the water in the group. This could be verified by measuring group heater current when water temp is higher than set point.

I am not sure what exactly is your procedure of this:

Then I tuned down the grouphead temperature and repeated the test and got the result that the real grouphead temperature was lower than it on the PID by 2 to 3 degrees C.

Could you please give us more details?

macaber8 wrote: Could you please give us more details?

For example,
1. Set the coffee boiler temperature 96C, grouphead 96C, needle valve full open, and got the water temperature about 92C.
2. Still 96C/96C, needle valve dialed to slow flow rate, and got the water temperature about 93C.
3. Set to 96C/94C, needle valve dialed to slow flow rate, and got the water temperature about 92C.