A question on Heat-Pump.

[lana]

Hi everybody,
I am designing an air-conditioning package with heat pump. Because the cooling capacity is relatively high (16kW) then I have decided to use TEV instead of cap. Tube. Therefore, I have too use two TEVs , one for cooling and for the heating cycle.
My question is this : can I install the heating cycle TEV's bulb on to the suction of the compressor (after the 4-way valve) so there will be no over-pressurization (in the valves bulb) during the cooling cycle? A schematic picture is attached.
Also, what would be the heating cycle TEV's capacity? (to select the orifice).
Thanks for any feed back.
Cheers.

[Andy]

Hi everybody,
I am designing an air-conditioning package with heat pump. Because the cooling capacity is relatively high (16kW) then I have decided to use TEV instead of cap. Tube. Therefore, I have too use two TEVs , one for cooling and for the heating cycle.
My question is this : can I install the heating cycle TEV's bulb on to the suction of the compressor (after the 4-way valve) so there will be no over-pressurization (in the valves bulb) during the cooling cycle? A schematic picture is attached.
Also, what would be the heating cycle TEV's capacity? (to select the orifice).
Thanks for any feed back.
Cheers.

Hi Lana

your expansion valve on heating should be slightly larger, but this depends on ambient during heating season.

Why not use a bi flow TEV which is designed for such an application (and a bi flow drier). probably best not to use a liquid receiver either.

hope this helps

Kind regards Andy

[lana]

Hi Andy,
Thanks a lot.
Bi-directional TEV and drier are not available at this moment so I must use this design.
What is the problem of using the receiver?
When you say the heating TEV must be slightly larger, how much? What should be the capacity which I have to select the TEV in the heating mode? Any idea?
Cheers

[Andy]

Hi Andy,
Thanks a lot.
Bi-directional TEV and drier are not available at this moment so I must use this design.
What is the problem of using the receiver?
When you say the heating TEV must be slightly larger, how much? What should be the capacity which I have to select the TEV in the heating mode? Any idea?
Cheers

Lana

you could use the compressor selection software for your compressor to find this.

Copeland and Bitzer are the names that come to mind

The size of the valve is all down to the capacity of the compressor and the system conditions you use.

The software will tell you provided you know your system pressures and temperatures you are designing from.

Receiver is not normally used with bi-flow valves.



Kind Regards Andy

[wkd]

Lana,
I've always mounted the TEV bulb on the compressor side of the 4 way valve on large HP's, otherwise when you change mode you will end flooding loads of liquid back to the compressor and that will never do.The question of the liquid reciever is difficult I have found that you require more charge in cooling generally than in heating so a reciever seems a good answer but it can hinder the system somewhat.Depending on how much more volume is required you may be able to get away with slighly larger pipes and do away with the reciever altogether.

[Lc_shi]

Hi lana
The usually design procedure is :
#Select the component based on main application,e.g,for cooling or heating:
#confirm the other mode's performance. If the cooling load differ greatly from heating mode,you need to consider the capacity adjustable.
#It's better to apply different TEV for cooling and heating,for it's different at most times.
#use suction receiver to at least buffer the extra refrigerant between cooling and heating mode .
#the TEV bulb is better to locate at the suction of 4-way valve to avoid high temperature impact while switching mode.

only for your ref
tell us what the design parameters of your product,may we say more exactly.

regards
LC

[lana]

tell us what the design parameters of your product,may we say more exactly.

Hi there,
thanks for your reply.
The capacity I am working on is 16kW cooling. The evaporating temp. is 5°C and condensing temp. 50°C.
The abmbient in summer is 40°C and in winter -10°C.
The cmpressor is Copeland scroll 5HP.

Cheers

[Lc_shi]

It should be ZR68 copeland.
How about the heat exchanger? Outside is tube-fin,inside is PHE?

regards
LC

[The Viking]

On a side issue;
The reason you normally not see receivers in bi-directional units is that most receivers only handles single direction flow, as you introduce the liquid at the top of the receiver and extract it from the bottom (thus in normal running conditions guarantees a liquid supply to the expansion device, reverse this and you will get gas to the expansion device)

Regarding the TEV's bulbs, there are TEVs specially designed for this type of applications but most MOP (Maximim Operation Pressure) designated valves should be OK.

[Peter_1]

That's how we've done it, the receiver for the HP is the bottom one, horizontally mounted

[lana]

That's how we've done it, the receiver for the HP is the bottom one, horizontally mounted

Dear Peter_1,
Thanks for the photos.
What are the two tubes on the wall which are diagonally mounted?
Cheers

[lana]

It should be ZR68 copeland.
How about the heat exchanger? Outside is tube-fin,inside is PHE?

regards
LC

Dear LC,
The compressor is DWM reciprocating.
Both HXs are tube in plates. They are both air cooled.
Cheers

[Peter_1]

Dear Peter_1,
Thanks for the photos.
What are the two tubes on the wall which are diagonally mounted?
Cheers

Liquid receivers, we hadn't enough space to mount standard receivers in the compressor compartment.

As usual, the space we have for our techniques is mostly verry narrow so that we must find a solution.
The filterd dryers are mounted on the Mitsubishi AC indoor unit, you can see that the compressors are stacked against each other.
You can see the tubes coming from the inclined receivers on the other side of the panel.
Other view is the collector for the plate cooling of the counter.
You can see on each side a spare tube yo insert the temperature probes.
Work was in progress while taking the pictures.

[Pooh]

Peter
looks very EN378 to me I would love to see the pressure test certs on those vessels, I am guessing this is a demonstration unit, if so I would like to see the front of it as it looks very interesting.

Ian

[Andy]

Peter
looks very EN378 to me I would love to see the pressure test certs on those vessels, I am guessing this is a demonstration unit, if so I would like to see the front of it as it looks very interesting.

Ian

Hi Ian

designed by Peter and fitted by his son

If you don't have shut off valves on the bits of pipe that are acting as receivers they are not a pressure vessel and don't require a releif valve
I'm pretty sure Peter has a relief valve somewhere

As I remember this unit is built on a lorry trailer as a mobile market/shop.

Kind Regards Andy

[tsounos]

greedings from Greece you guys have some interesting stouf.

[Peter_1]

Peter
looks very EN378 to me I would love to see the pressure test certs on those vessels, I am guessing this is a demonstration unit, if so I would like to see the front of it as it looks very interesting.

Ian

There's no pressure relieve valve on it Andy.

EN378 7.4.2. Protection of the refrigeration system (I have here only the French version in front of me but the article numbers should still correponds in another language) says that the systems we've build must have at least a thermal fusible plug or a safety relief valve to release excessive pressure or(!) they must be protected by a system that protects them against exsessive pressure, as described in 7.4.2.2. or (!) 7.4.2.4.

7.4.2.2. states that we can chosse between a, b, c or d where a says that there must be only one protection against excessive HP (a safety pressure switch) for systems with a capacity lower then 100 kg in the system and with a compressor pumping less then 25 l/s.

Is this correct?

Andy, does this change if there are 1 or 2 valves on the receiver? I don't think it but as I said, I only think this because I can't find something in EN348 which says something different.

We pressurise these system on 25 bar for some days (not some hours as many do and 25 bar is a lot more then law demands) and we provide then the pressure certificats ourself.

This is indeed not a demo unit we have build.

I took today some additional pictures of this unit, it's now +/- 1 year old and it was in our shop for some maintenance just before the warranty ends.
I told the owner that we were talking about his AC receiver, so be careful he's perhaps reading this thread (Are you reading now Pol )
Just joking, he's perhaps reading it but I mostly don't have secrets for my clients.

[Andy]

Andy, does this change if there are 1 or 2 valves on the receiver? I don't think it but as I said, I only think this because I can't find something in EN348 which says something different.

We pressurise these system on 25 bar for some days (not some hours as many do and 25 bar is a lot more then law demands) and we provide then the pressure certificats ourself.

.

In general if you can shut off a vessel and it could be overpressurised it needs a relief valve. The rating of the relief valve depends on the fluid used and if it is air or water cooled. Strength testing is then by PED 1.0 to 1.3 times the releif valve setting (we use 1.5) so R22 aircooled would be 22 bar releif by 1.5 33bar. Or 24.1 for R404a aircooled, with a strength test pressure of 36.15bar.

Kind Regards Andy

[Pooh]

Andy
as far as I know any vessel that can be exposed to more than 2bar litres is a pressure vessel ie. volume times pressure so if you have a 0.1 litre vessel at more than 20 bar it needs a releif valve. I was caught out on this on a job I specked were the liquid drier needed a releif valve because it could be valved off.

Ian