Power control based on return T or analog signal

[barbaz]

Hi all,
I'm very happy with my RTB 16 but I'd like that will be nice that the boiler adapt it's power also looking on the return temperature and not only if it is able to mantain a particular temperature. I'll try to explain me better:
My RTB is connected directly to a puffer with an anti condensation valve (caleffi 280).
I don't need very high temperature in the puffer (65°C is enough for HUW and heating) and so the boiler has been setted to mantain 70°C. What's happening is that the anti condensation system always make the return flow at 55/59°C, and the boiler obviously mantains low power. But in fact both the top and bottom part of the buffer is at 45/40° and i need power!
So, can I control this for example with T3 sensor? or is it possibile to control the power with a 0-10v signal (that my climatic system can manage)?

thanks for suggestion!

[MHES]

Hi,

If the boiler is at 70^oC and return at 55/59^oC while the burner is running low power, then your flow is simply too low.
The "power loss" in the boiler (that power the burner needs to produce) is boiler (temp. - return temp.) x flow, so if you increase the flow through the puffer, the it might help.

Otherwise the "cooling effect" in your puffer is simply too low to adapt the power from the boiler/burner.

To regulate the burner according the return temperature won't help you, it will just increase the boiler temperature, which you also could do yourselves.

Regards
Michael

Hi all,
I'm very happy with my RTB 16 but I'd like that will be nice that the boiler adapt it's power also looking on the return temperature and not only if it is able to mantain a particular temperature. I'll try to explain me better:
My RTB is connected directly to a puffer with an anti condensation valve (caleffi 280).
I don't need very high temperature in the puffer (65°C is enough for HUW and heating) and so the boiler has been setted to mantain 70°C. What's happening is that the anti condensation system always make the return flow at 55/59°C, and the boiler obviously mantains low power. But in fact both the top and bottom part of the buffer is at 45/40° and i need power!
So, can I control this for example with T3 sensor? or is it possibile to control the power with a 0-10v signal (that my climatic system can manage)?

thanks for suggestion!

[barbaz]

Hi Michael,
tank you for your kind reply.
Probably anticondesnation valve has a too low kvs. you are right... I've tried to speed up the pump but it didn't change. So I looked at the specification of the anticondensation.
Can you help me on how to  calculate the correct flow between boiler and puffer?

thank you again!

[MHES]

Hi,

Well, I can help you calculate the needed flow through the boiler in ordet to "move" a specified heating effect.
Units are:
Temperature in ^oC
Flow in l/h
Effect in kW
The formula is:
Flow = Effect x 860 / (outlet temperature - return temperature)

So, if you have an outlet temperature of 70^oC and a return temperatur of 59^oC,
You need flow of 78 l/h per. 1 kW effect in the boiler.

Let's say your boiler run with min 2 kW in low and 16 kW in high, it means you need a min flow of 156 l/h and a max flow of 1251 l/h, in order to be able to "move" the heating effect out of the boiler, depending on the burner effect.

Best regards
Michael

Hi Michael,
tank you for your kind reply.
Probably anticondesnation valve has a too low kvs. you are right... I've tried to speed up the pump but it didn't change. So I looked at the specification of the anticondensation.
Can you help me on how to  calculate the correct flow between boiler and puffer?

thank you again!

[barbaz]

So, if you have an outlet temperature of 70^oC and a return temperatur of 59^oC,
You need flow of 78 l/h per. 1 kW effect in the boiler.

Let's say your boiler run with min 2 kW in low and 16 kW in high, it means you need a min flow of 156 l/h and a max flow of 1251 l/h, in order to be able to "move" the jeating effect out of the boiler, depending on the burner effect.

Fine! thank you a lot.... this drive me into another problem. the outlet temperature of boiler is exactly 70°C, and return (after anticondensation) is 59/60°C. My boiler is exactly an RTB 16, so your calculation fit my needs...

but the caleffi 280055 that I'm using has a Kvs of 3200 l/h , so it shouldn't be the problem, right?

[MHES]

What about your pump ?
Can/do the pump supply enough flow ?

Regards
Michael

So, if you have an outlet temperature of 70^oC and a return temperatur of 59^oC,
You need flow of 78 l/h per. 1 kW effect in the boiler.

Let's say your boiler run with min 2 kW in low and 16 kW in high, it means you need a min flow of 156 l/h and a max flow of 1251 l/h, in order to be able to "move" the jeating effect out of the boiler, depending on the burner effect.

Fine! thank you a lot.... this drive me into another problem. the outlet temperature of boiler is exactly 70°C, and return (after anticondensation) is 59/60°C. My boiler is exactly an RTB 16, so your calculation fit my needs...

but the caleffi 280055 that I'm using has a Kvs of 3200 l/h , so it shouldn't be the problem, right?

[barbaz]

What about your pump ?
Can/do the pump supply enough flow ?

Yes,
it's the pump supplied with NBE RTB 16 (it seems an IBO MAGI 25-60). I've the same effect with auto or fixed speed (22 or 44watt, is the same); with auto it sets on 15/16w

[MHES]

Hi,

What is the return temperature from the puffer, before the anti condensation valve ?

Best regards
Michael

What about your pump ?
Can/do the pump supply enough flow ?

Yes,
it's the pump supplied with NBE RTB 16 (it seems an IBO MAGI 25-60). I've the same effect with auto or fixed speed (22 or 44watt, is the same); with auto it sets on 15/16w

[barbaz]

Hi,

What is the return temperature from the puffer, before the anti condensation valve ?

Hi Michael,
sorry for late reply but I was out for work last week and 've made some tests this weekend.
I've checked the dirty separator filter (https://www.caleffi.com/italy/it/catalogo/dirtmagr-defangatore-con-magnete-corpo-tecnopolimero-545305) but it was ok, just some dirt at the bottom.
The return temperature before the VAC is always at the same T of the buffer bottom (usually 40°), when the buffer start becaming full it grows up of course.

I've made some tests with P and I:
P=12.5 and I=0.05 (my previous regulation): it was ok when hot request is average, the boiler always run very low. problem start when one or two circuits start asking hot water, this bring buffer T very low and the boiler never increases power.

P=5 and I=0.1, a little bit better, the average power is higher (30/40%) and so also the fuel consumption is better. I've edited the system schedule so it never start 2 or more circuit at the same time and this give me a lot better configuration. The problem start when I turn on a circuit with fan coil that ask for hot water. also in this case the buffer T goes down but the boiler run at the same (low) power.

Now I'm making some tests with P=5 and I=0.2, i'm thinking that I make the power very high and P start decreasing it it it is too much.

I'm increasly convinced that with my configuration with buffer the boiler must be driven by the buffer top temperature, but i'm hoping to be wrong and hoping find a good setup

thanks for your interest and help Michael!

[MHES]

Hi,

Heating is not magic 
If your boiler can maintain the outlet temperature at setpoint (70^oC) with return temperature of 55/59^oC and low effect, and you want the effect to be higher, the only way is to increase the flow through the boiler.
The flow is limited by the pump capacity and the “pipe-work resistance”.

Best regards
Michael

Hi,

What is the return temperature from the puffer, before the anti condensation valve ?

Hi Michael,
sorry for late reply but I was out for work last week and 've made some tests this weekend.
I've checked the dirty separator filter (https://www.caleffi.com/italy/it/catalogo/dirtmagr-defangatore-con-magnete-corpo-tecnopolimero-545305) but it was ok, just some dirt at the bottom.
The return temperature before the VAC is always at the same T of the buffer bottom (usually 40°), when the buffer start becaming full it grows up of course.

I've made some tests with P and I:
P=12.5 and I=0.05 (my previous regulation): it was ok when hot request is average, the boiler always run very low. problem start when one or two circuits start asking hot water, this bring buffer T very low and the boiler never increases power.

P=5 and I=0.1, a little bit better, the average power is higher (30/40%) and so also the fuel consumption is better. I've edited the system schedule so it never start 2 or more circuit at the same time and this give me a lot better configuration. The problem start when I turn on a circuit with fan coil that ask for hot water. also in this case the buffer T goes down but the boiler run at the same (low) power.

Now I'm making some tests with P=5 and I=0.2, i'm thinking that I make the power very high and P start decreasing it it it is too much.

I'm increasly convinced that with my configuration with buffer the boiler must be driven by the buffer top temperature, but i'm hoping to be wrong and hoping find a good setup

thanks for your interest and help Michael!

[barbaz]

Heating is not magic 
If your boiler can maintain the outlet temperature at setpoint (70^oC) with return temperature of 55/59^oC and low effect, and you want the effect to be higher, the only way is to increase the flow through the boiler.
The flow is limited by the pump capacity and the “pipe-work resistance”.

You are right.... I'll try again increasing the flow of the pump, I'll make some test with different curve.

Last option is to read buffer T with a raspberry and setting the power of the boiler via API

[barbaz]

Heating is not magic 
If your boiler can maintain the outlet temperature at setpoint (70^oC) with return temperature of 55/59^oC and low effect, and you want the effect to be higher, the only way is to increase the flow through the boiler.
The flow is limited by the pump capacity and the “pipe-work resistance”.

Just for reference... if someone else is looking for the solution of the some problem

At the end I've decided to adopt the speed of the boiler pump based on the output of my climatic control unit.

So if the control unit out 10v I put the pump at high speed, if 5V middle speed, if 0v I regulate the pump at minimum speed.

In this way the boiler adapt its power consequently ))

There is some pump that accept 0-10v (but starting from 3v), someone else accepting pwm, etc etc
In my case I've used an old asyncronous pump with an inverter, and the inverter is drived directly but the 0-10v signal. Other possible solution can be an arduino that read 0-10v and out a pwm 100%-10% signal (inverted) for a grundfos alpha 1L.

Thank you all for your support!!!