leak testing with OFN

[davej]

when leak testing with OFN what is the generally accepted pressure drop. is there a figure? i realise there will be some drop depending on temperature variation but i just wondered what you guys allow.

[SteveDixey]

when leak testing with OFN what is the generally accepted pressure drop. is there a figure? i realise there will be some drop depending on temperature variation but i just wondered what you guys allow.

If you are using ***** on hermetic systems, none really.

On open drive industrial systems, the simplest is for leaks after re-assembling a pump or compressor and before returning it to service. IoR recommend that the leak test pressure should be at 1.1 times the working pressure, held for an hour and not losing more than 10%.

Steve

[taz24]

when leak testing with OFN what is the generally accepted pressure drop. is there a figure? i realise there will be some drop depending on temperature variation but i just wondered what you guys allow.

Do you mean pressure drop due to temp or pressure drop due to a leak

Cheers taz.

[davej]

if i explain breifly , we are pressure testing some ground loops (for ground source heat pumps) and as they have been used we believe, although we have vac'd the pipework, there is probably some oil down in the loops and we were debating that when pressurised what would be an acceptable pressure loss/drop wihtout there being a possibly leak. does that explain it?

[taz24]

acceptable pressure loss/drop wihtout there being a possibly leak. does that explain it?[/quote]


I take it that the ground loop must be the primary evap with refrigerant flowing through it. I can't remember if you stated the type of gas in the system. You need to work out the standing pressure of the gas at 55c and then X it by 1.3 to strength test and drop it back to 1.1 for the leak test. There should be no noticable drop in pressure. The ground loop would be at a constant temp so any pressure drop would be a leak. The ground loop should be a constant sigle pipe with no conections to leak. Any conections in the system should come back to the central inspection pit where the valves and TEV should be sited. To prove with out doubt that it is gas tight, I would leave it under pressure for 24 hours. To sum up if the temp is constant which it would be in the ground you should see no drop.

Cheers taz.

[Peter_1]

We pressurise loops - in fact all our systems - at 20 bar bar (290 psi) even 25 bar (362 psi) during 1 or more days (sometimes a week) and the pressure may not drop more then 1 or 2 lines on your manifold (0,2 bar or 3 psi)

Especially while testing a ground loop with OFN, you don't have a temperature difference. If you start at 290 psi at 55°F and temperature drops to 51.8°F, then you will have a pressure drop of 2.4 psi.
Normally, the temperature remains stable with a ground loop as long as the system isn't running. (is in fact what TAZ 24 said if I re-read now , the day after the whole thread)

Do you use protected copper or bare copper wit this DX system if I may ask?
What's the brand of the heatpump or is it an own construction?
3/8 or 1/2 piping?

[davej]

Hi Guys, thanks for your input, the systems are not running we are trying to confirm the pipework integrity, and following your comments we doing the right things.

As for you question Peter, they are American ECR heat pumps made in Florida,the 1/4 line is protected but the 1/2 inch suction side is not protected.We did not install these loops which go 30m down that was done by other, also they are set in heat transfer grout.

[Peter_1]

I suppose the heat transfer grout is a mix with concrete (cement) as one of the substances.

Is cement not too agressive for the bare copper? Most grouts are designed or composed for a better heat transfer of PE tubes.

Isn't there a cathodic protection installed or don't you use this?

What COP's reach this systems? We achieve +/- 5.

[davej]

Hi peter, We have only recently started working with these systems and we are asking the importers similar questions, however, the grout is, and im not sure of the exact spelling, a bekonite paste (?) and there is a plastic sheath on the 1/4 tube and acid testing of the soil should be carried out and anode used where necessary.as for the cop's some debate at the minute as to the actual figures and they are being tested relative to uk use as oposed to florida.

[Peter_1]

I just want to take the attention to the fact that these systems reach a COP of 5 where all the air/air manufacturers reach 4 as long as weather conditions and inside conditions are optimum.

If I take a standard heat pump of a well known manfuacturer, then this gives me an average of 4 at standard conditions (20°C inside and 7°C outside 68°F/44.6°F) but as soon temperature drops below 0°C (32°F) then this becomes 3.34 and when it's outside -5°C (23°F), then this decreases already to 2.95.

This where the GSHP stays firmly on 5.

OK, these temperatures doesn't happen not for long but heatpumps are installed all over the world.
An air/air in most parts of Canada is therefore a bad solution.

[refteach]

Davej the type of paste is probably Bentonite Paste, it is made from Bentonite Clay which has a tendency to expand when it is wet which helps seal any joints or gaps.

[Peter_1]

There are many different mixtures of grouts available.
If you look in the manuals of IGSHPA, then you find different grouts.
If you search through the patent databases, then even much more grouts are available.

The purpose of the grout is to seal the different layers that have been drilled so that they can't contaminate each other and also and especially to improve heat transfer.
Many use also the same material that was drilled out of the borehole.
A good technique is inserting a tube inside the copper coil down to the bottom of the hole (inserting it together with the PE or copper coil )

Then pumping the grout downwards the hole till it overflows at the surface. You're then sure that the hole is complete filled.
But, cement is aggressive for copper.

[Peter_1]

Oh, I forgot something which is important: the figures given by the air/air manufacturers are for outdoor units, for systems running in normal mode.

So, as soon they go in defrost - which happens often in a day - they then spoil a lot of energy. The energy to defrost comes from the indoor units which will lower the indoor temperature or at least the coil temperature. To avoid cold drafts, some then install electrical heaters or to make that there's sufficient energy available to
defrost the outside coil.

So after an expensive defrost of let's say 5 minutes, the unit needs to run another 3 to 5 minutes or more to achieve the desired temperature. So, a complete defrost needs more time then only the defrosting time.
This is a total of 8 minutes that the compressor spoiled a lot of energy.
I measured this in the past on an actual machine VRV/VRF and there was a defrost cycle every 1.5 hour which lasted +/- 15 minutes.

These figures are never given in the manuals but decreases the overall COP seriously.

A GSHP hasn't all these disadvantages.

[taz24]

Davej the type of paste is probably Bentonite Paste, it is made from Bentonite Clay which has a tendency to expand when it is wet which helps seal any joints or gaps.

I would agree with this. But putting a primary coil into the ground without any sheathing would be desastorous for the copper. Primary heat collector coils are more efficient though as you do not have to pay to circulate the water round the system.

Cheers taz.

[Peter_1]

Primary heat collector coils are more efficient though as you do not have to pay to circulate the water round the system.

They're indeed much more efficient but also for a second reason: you don't need a water/refrigerant HE, so you can raise evaporating temperature with at least 6K.

[VIXS]

Hi There Bud

Leak testing with OFN

For evert 10 deg difference you can expect a drop of 0.7 bar

Example:at 20 deg c and a pressure of 20 bar if the temperature drops to 10 deg c then the pressure reading will be 19.3 bar

Hope that sorts you out

Keep it simple

[Latte]

Hi all,

Dont know if they still do but Fosters used to use heluim for leak checking new cabinets, anyone doing that out in the field. I would suspect not due to cost.
Regards

Fatboy

[Peter_1]

With new plants, in many cases we even don't perform a leak check with a sniffer or a tracer gas.
We pressurise the system for days at 25 bar (362 psi) and if pressure doesn't decrease, then we conclude that the system is tight enough
We allways try to make that the tubes are fitted first and then pressurise immediately the system. We then begin with all the electrcial stuff.