Performance of In-House Cooling System

[teknomania]

Hi Guys,

I am trying to find the equations to obtain the performance of an in-house cooling system (AHU, floor cooling, fan coil etc.). I want to find the performance equations (of an in-house cooling system) i.e. resulting in return temperature as a function of the supply temperature, the original cooling design capacity and the set-point for indoor temperature. The picture below is exactly what I want to result by use of the performance equations (that I am looking for). Of course with the performance equations I would like to be flexible of changing the parameters and see how the return temperature changes (e.g. by changing set-point indoor temperature or by changing the current cooling load of the cooled zone).

The source of the picture is "UPONOR - Radiant cooling design manual - Embedded systems for commercial applications (click)"

In the case of heating, the equations regarding in-house radiator heating systems can be found in "Gary Phetteplace - Optimal design of piping systems for district heating (click)". In this publication, you can find the equation showing the performance of a radiator system by means of obtaining the return temperature as a function of the supply temperature, indoor temperature (set-point), original design capacity and the original logarithmic mean temperature difference. There, the original LMTD can be calculated by Eq. 3-2 and the return temperature by Eq. 3-19 in short [there is also need to calculate the original GMTD (Eq. 3-5) and initial value of the return temperature (based on the GMTD -as starting point to be used in the iteration given in Eq. 3-19), its expression given in Eq. 3-17].

Another example for heating systems can be this web page: Heat Emission from Radiators and Heating Panels (Click)

Is there a way to change the equations given in "Gary Phetteplace - Optimal design of piping systems for district heating" for in-house cooling systems?

Waiting for your fruitful comments..

Kind Regards.

 

[Drazen]

theoretical model for system you described is based on navier-stokes equations, non-linear differential equations of second order that don't have real solution and can be solved by numerical iteration of different complexity.

equations you mentioned present simplified subsystems, that are limited to narrow boundary conditions, which are usually called "assumptions". if you don't follow "assumptions" strictly they are useless, and you cannot combine them as their "assumptions" do not correlate in full.

that is level of job for university/scientific projects. university usually don't set up models as it requires lot of high-skilled work nobody is willing to pay for (while the same models are set for aeronautics as sponsors have money), so universities usually make measuring and observing projects limited to some typical systems.

 

[dbill74]

You need to be more specific in your question and what you are looking for when you say "performance". By "performance" do you mean system efficiency, AHU capacity, space temperature over time or something else.

 

[teknomania]

Hi dbill74,

What I mean by saying performance of an in-house cooling system is what will be the return temperature (from the in-house cooling system) and the required mass flow according to different rates of the supply temperature, and current cooling capacity.

I hope this is clear.

 

[willard3]

There are way too many variables affecting the load for a formula and what you really want is a lot of data on your own system.

This can only be solved empirically.

 

[teknomania]

Dear All,

I modelled the in-house cooling system (in question) as a cross-flow water-to-air heat exchanger and willing to have the response (of return temperature) according to changing supply temperature.

Now I get stucked in some point. How can I reach to equations for performance (or rating) measure of a heat exchanger (any type)?

Here is one example of source (that I am looking for but this one is not clear to me): Predicting the Performance of Heat Exchangers (Click). Another good example for performance measure is given in SWEP online tool (click)

Would you please give me another sources describing the calculations and/or methods for performance (or rating) measures of heat exchangers (based on LTMD, or e-NTU methods or any other)?

Kind Regards.

 

[chicopee]

Get a copy of a mechanical engineering handbook and study the sections on heating and cooling. There are tons of formulae that will be presented. ME handbooks could be Mark, Kent and also Perry's Chem. Engin handbook.

 

[teknomania]

Dear All,

I found the solution to my issue in the book of "Air Conditioning Engineering" written by W.P. Jones. The example at the page 291 is exactly what I need for my model of in-house air conditioning system. For your information.

Kind Regards.