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poliskarma
09-10-2008, 02:42 PM
Hi,

I am in my last year in the university and I am working in a group to design an intelligent fridge system. Basically , instead of using a thermostat to control the relay of the compressor, my group need to design a control mechanism based certain conditions (such as turn on the compressor more regularly at night when electricity price is cheaper (Economy 7)).

In order to do that I first need to simulate the dynamics of the fridge on Matlab. My question is, is there any guideline to model/simulate the conditions of a fridge being used? For example, what kind of the disturbances we need to consider(opening fridge door/putting hot food).

Cheers.

casstrig
09-10-2008, 06:04 PM
Turning a fridge compressor more often at night isn't practical as the majority of the heat load will be during the day as the door is opened and in the daytime the ambient temp is always higher the important parameter controlling the usage of the compressor must be the interal temperature.

icecube51
09-10-2008, 06:38 PM
to design a fridge you have take consideration whit;
input of goods, quantity and specific heat load.
lights and what kind, power or watt and how many.
how many people in and outgoing,staying for work inside.
opening and closing of doors, time and size of opening.
are there plastic flaps behind the door. forklifts ??
is the fridge inside the building or outside.building material of the fridge
is it north or east or south. windows ?

just a few things to take in consideration,;)

Ice

Chef
10-10-2008, 07:31 AM
Hi Poliskarma

What kind of fridge system are you going to design, is it a household unit or a walkin unit (or other).

Much of the work I have been doing over the last months would probably be very useful in your project as it is almost exactly the same.

It mainly consists of systems dynamics modelling of the system as a whole and how it responds to changes in load, temperatures etc. Most of it is written in Excel and Octave and whilst Octave is similar to Mathlab the latter is more likely to be already at the Uni.

You will need the properties of refrigerants as a subroutine call from within Mathlab and probably the best one is FluidProp, is has library links direct to Mathlab. You will need to get the Uni to establish a license for this, although the basic module is free with a limited number of refrigerants you would more likely need some of the newer blends to have a more generalised code.

You could to model it with feedback models by defining G the gain element as a complex function or you could do with straight code using lots of IF statements. The most dificult part is that the system as a whole has 'limit' points ie a parameter may obey a simple square law for instance until it hits a set limit and then it changes and may obey a constant or reciprical law, get these points right and it becomes a lot simpler.;)

Let me know your system type.

Borrowing a phrase from a famous American Iceman "Are you sure you want to do this"

Chef