TEV Pressure Difference

[SkyWalker]

Hi guys, let me start by wishing everyone a happy new year! (better late than never )

I was thinking about a system which was over condensing, causing minimal temp lift and what effects it has on the system, I was wondering at what pressure difference over a TEV would refrigerant stop flowing?

also, if this where to happen how would the system behave? would it trip on LP as refrigerant gets pumped into the high side? (suppose it probably depends on system size) or would the high side raise in pressure and then refrigerant would flow over TEV for a short while then keep repeating this over and over with little refrigeration effect?

also what pressure difference over other types of expansion device, capillary and EEV mainly before refrigerant will stop flowing?

thanks for any help in advanced! love the learning

[mad fridgie]

Think of your expansion device as just a hole (variable) so as long as there is a pressure difference there will flow, what your are trying to describe is how the system is designed (choice of valve) If at design you have big pressure differences, you have a small hole to give the right flow, so when pressure difference becomes lower and less than the max adjustment of the hole then flow will reduce. So why not just install big adjustable over sized holes; Effectively this what your are doing with EEV, but the mechanical adjustment is different to that of a TEV. An EEV has alot of mechnical movement so control on the seat can be achieved, with aTEV the mechanical movement is very small, so controlling the area on the seat is difficult (open to much, closed to much "hunting')

[Magoo]

you mentioned the "OC " word, not, it is called low discharge pressure.

[SkyWalker]

Hi magoo, I was thinking in terms of a winters day with no fan speed control and the condenser is rejecting to much heat as it is now over sized hence " over condensing" causing low discharge pressure.

[Peter_1]

Many TEV's like Sporlan, Danfoss works fine till 4 bar DP.
So mostly, you will not face problems with over condensing, although I don't like that term.
The lower you condense, the better for your the environment.

Due to the low condensing pressure, your compressor will pump much more efficient resulting in a lower evaporating temperature. This will lower the RH in your cold room.
But due to the lower evaporating temperature, your evaporator capacity will increase a lot ( Q= m.c.DT and DT increases), so running time will be less.

You wrote "also, if this where to happen how would the system behave? would it trip on LP as refrigerant gets pumped into the high side? Where is refrigerant dumped in the high side?

As MadFridgie explained, it will never stop flowing.

[cool runings]

Many TEV's like Sporlan, Danfoss works fine till 4 bar DP.As MadFridgie explained, it will never stop flowing.

I agree with Peter and what the others say.

I was always told the differance is between 5 and 7 bar
dependant on manufacture.

Some compaies are deliberatly running the head preasure as low
as possible and then pump up the liquid line pressure with a hydrolic pump.

All the best

.

[young gun]

ok, what about if you have very high discharge pressures...... because of badly located condensing units, and they systems have even been undercharged to compensate.... and you still have a large amount of vapour going through your tx valve..... can that fact you still have high pressure vapour going through your valve almost make your valve act non existant??

[SkyWalker]

thank you peter_1 and cool runings

[monkey spanners]

ok, what about if you have very high discharge pressures...... because of badly located condensing units, and they systems have even been undercharged to compensate.... and you still have a large amount of vapour going through your tx valve..... can that fact you still have high pressure vapour going through your valve almost make your valve act non existant??

What ever heat isn't removed from the refrigerant in the condenser has to be removed in the evaporator before it can start cooling the product, so you'd have a low duty (insufficient liquid at txv, high cond temp) and a high suction superheat again due to insufficient liquid feed to the txv. So i would expect the valve to modulate towards the fully open to try and reduce the superheat.
It would all depend on hot undercharged and how hot it is running etc.