Solving a Problem with LPHW Radiator

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In summary, the first diagram would show the relationship between the control signal and the radiator heat output. The second diagram would show the relationship between the room temperature and the radiator output heat.
  • #1
jami8337
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I am trying to solve a problem regarding an LPHW radiator, of which the heat output is controlled by adjusting the LPHW flow rate. The relationship between the flow rate and the radiator output can be approximated by a first order transfer function with a time constant of 1 minute. The heat output is adjusted by a control signal directed to a final control device that determines the LPHW flow rate.

I now need to draw two open loop block diagrams The first showing the relationship between the control signal and the radiator heat output. The second of the relationship between the heat output and the room temperature.

I am at a loss on what to do for the first diagram, however it may just be me overthinking it. Would it simply be:

i ----> Controller -----> LPHW Valve -------> Heat Output

Any insight would be greatly appreciated

Thanks
 
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  • #2
I think you probably need to add a block showing the first order transfer function. Something like..

I---> Controller -> LPHW Valve --> LPHW Flow rate ---> Transfer function ----> Heat Output

Replace "Transfer function" with the actual equation.

Not sure how to do the second one. I'm familiar with steady state heat loss calculations (you need thing like the thermal resistance of the walls and the temperature gradient across them) but your question suggest a dynamic situation (for which you probably need information on the thermal mass?).

Sorry that's the best I can manage.
 
  • #3
Thanks for your help, I think i can draw both the block diagrams, but I am hitting a wall when having to derive the transfer function for the first one. This would be based on the energy balance equation i believe, but i am a bit lost trying to derive that. I have come up with:

(TW-Ti)/R

Where Tw is the temperature of the LPHW, and Ti is the room temp...
 
  • #4
Okay here is what i have come up with:

Temperature LPHW = θL
Temperature Output = θO
Heat Flow rate = Q

Q=(θLO)/R

Assuming no losses. The heat transferred from the LPHW alone determines the 'Radiator output' to the room. Therefore the rate of heat transfer will determine the rate of change of the radiator output, hence:

O/dt = Q/C (C = Capacitance)

Then:

O/dt = (θLO)/RC

I can then rearrange this and take a laplace transform to give me the transfer function. Does this sound like the right sort of track to be on?

Thanks!
 
  • #6
Whats up? Any further news regarding these efforts?
 

What is LPHW?

LPHW stands for Low Pressure Hot Water. It is a heating system that uses hot water circulated through radiators to heat a building or space.

How does a LPHW radiator work?

A LPHW radiator works by using hot water from a central boiler system to heat up metal fins or tubes inside the radiator. The hot water transfers heat to the metal, which then radiates warmth into the surrounding space.

What are the benefits of using LPHW radiators?

LPHW radiators are energy efficient, as they use hot water instead of electricity to heat a space. They also provide consistent and comfortable heat, are easy to install and maintain, and can be controlled with thermostats for individual room temperature control.

How do you solve a problem with LPHW radiator?

The first step in solving a problem with LPHW radiator is to identify the issue. This could be a leak, a blockage, or a malfunctioning component. Once the problem is identified, the next step is to troubleshoot and determine the cause. This may involve checking the water pressure, inspecting the valves or pipes, or testing the thermostat. Finally, the problem can be solved by repairing or replacing the faulty component.

Can LPHW radiators be used in any type of building?

Yes, LPHW radiators can be used in a variety of buildings, including residential homes, commercial buildings, schools, and hospitals. They are a popular heating option due to their versatility, energy efficiency, and effectiveness in distributing heat evenly throughout a space.

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