Algorythm

[ascorone]

Hello people,

I'm new here. I tried to solve problem myself, but nothing going right. I'm constructor from Lithuania, which is working with ventiliation products, specifically working with refrigeration, actually with construction. This is new experience for me, so I came here to consult with proffesionals. Now I'm trying to make components selection algorythm. I'm gonna write you my thoughts.

First of all, I'm doing cooling block (evaporator + compressor + condenser), other components like electronic expansion valve, receivers and etc. does not dominate here, only main 3 components. I get a lot of clients applications form about that cooling block (where the main input parameters are presented), as I mentioned before I'm making selection algorytm to make selection process much faster.

I wrote the selection process for cooling, but I want to add heating too (heating process is achieved by 4-way valve and etc., when the whole cycle is reversing). I'm gonna split system into cooling and heating.

COOLING

1 step. Evaporator selection -> Client presents T1in RH1in and T2 out (desired temperature till what air must be cooled), so there's nothing hard (we get evaporator (cooling) capacity - P1.
2 step. Compressor selection -> There's nothing hard too (P1kompressor is equal P1 evaporator capacity, so we get P2 (compressor power input)).
3 step. Condenser selection -> evaporator capacity (P1) + compressor power input (P2) = condenser capacity (P3). To check if the condenser is picked up right, I use formula where condensing temperature is 3 ~ 5 C higher than condenser outlet temperature. If the condenser selection is wrong, I'm changing temperatures and do recalculations from 1 step. I forgot to mention that in condenser selection client presents T1in RH1in, but it don't present T2out, but is neccesary for me because I can use (mentioned above) my checkpoint (about 3 to 5 difference).

HEATING

I talked to our company technician and he said that for heating mode calculation process is the same (I mean step by step as written above). Yes the selected evaporator and condenser coils are fixed (I mean it can't be change fin space, number of tube rows and so on). When 4way valve reverses, evaporator turns into condenser and condenser turns into evaporator. Now about calculations. As I mentioned, coils structure are fixed, I only need to set temperatures values. I've read on internet (don't remember website), but such heating type depend on winter outdoor temperature. In most cases such heating type is as used as secondary heating source and actually we need additional heating element to satisfy client heating demand (it depend on winter outdoor temperature).

1 step. Evaporator selection. -> I have T1in RH1in, but I don't have temperature out.
2 step. Compressor selection. -> I can't select compressor, because I don't have evaporating temperature.
3 step. Condenser selection. -> I only can select condenser, because I have T1in RHin and T2out (by client demand).

So my questions about heating mode:

1. How to determine evaporator temperature out? Maybe there's formula like in cooling or something like that?
2. Maybe there's conditions (temperatures) till what this kind of source, would satisfy client heating demand on winter) and when we need additional heating equipment?
3. I think it's wrong to select condenser by client heating demand, because then I can't select evaporator and compressors?
4. How to determine maximum such block heating temperature (till what maximum temperature condenser could heat air without additional equipment)?

Thanks for answers. If you don't understand something, please write and I'll try to explain as much as I can.

[Rob White]

.

I don't know much about component selection algorithms

But I do know that when you have a fridge system it must be balanced.

The amount of heat that is absorbed by the evaporator and is added too
be the compressor must be rejected by the condenser. That means the
condenser is bigger than the evaporator, when it is in cooling mode the
system is balanced but if you put that system into heating mode, your
evaporator becomes your condenser and your condenser becomes your
evaporator.

That means in heating mode you will be absorbing more heat than your evaporator
can reject so sizing is important but so is control. How do you plan on using the
selection algorithm to allow for the change in duty as the thing changes from
cooling to heating?

I don't think you can do it with only 3 components (compressor, evaporator and condenser),
I think you have to have all four components (compressor, evaporator, condenser and metering device).

It is the control of the metering device and other components that regulate the amount of duty
your system absorbs and rejects and you can't possibly hope to complete the algorithm
if you don't factor all four components into it.

Rob

.

[ascorone]

Rob thanks for reply. Yes you're right on heating evaporator becomes condenser and condenser becomes evaporator. I forgot to mention that, I'm selecting variable speed compressor with frequency converter. Yes you're right too, that for all algorithm metering devices are important, but this algorithm is just for simple selection. Other stuff of metering devices will be calculated according to specific cycle points (such as CoolPack software does, like pressure, temperature).

To make this thing more understandable, we are doing ventiliation units (starting from 5000 m3/h) at which we are trying to intergrate compressors cooling block.

[Rob White]

Rob thanks for reply. Yes you're right on heating evaporator becomes condenser and condenser becomes evaporator. I forgot to mention that, I'm selecting variable speed compressor with frequency converter. Yes you're right too, that for all algorithm metering devices are important, but this algorithm is just for simple selection. Other stuff of metering devices will be calculated according to specific cycle points (such as CoolPack software does, like pressure, temperature).

To make this thing more understandable, we are doing ventiliation units (starting from 5000 m3/h) at which we are trying to intergrate compressors cooling block.

Sounds like you are on top of it all and like I said I
don't know much about the selection software but
good luck with the project.

Sounds interesting.

Regards

Rob

.