New system tripping on low pressure??

[DTLarca]

Well perhaps you're right ... but this guy is on a commercial contract ... he has to get a system running, keep client happy and a reputation to maintain. If he fixes this problem, by any means, the client will be pleased. If on the other hand he pisses about fannying over theoretical issues of flow and bypass factors etc, the client ain't going to be very happy.

In a real world Gary, the pressure is on when some one has paid for a system and it isn't working as specified. They don't care about theories they want results, now , not whenever.

I feel for this guy, he needs some help to get him or the system out of the mire. He'll be reading all of these posts and be getting lost with the runaround, he needs to be offered sound practical advise that he can act on. If he were in an R & D shop then it would be different I'm sure.

This is basic commissioning knowledge. If you want to get into the design then we can go there but I think that would be unnecessary considering the scope of practicalities here.

Gary asked about the bypass factor principles I mentioned - not the original poster. So the answers were not addressed to the original poster - only to Gary. The comments about this being a fresh air application possibly being asked to operate out of range were aimed at the original poster and all other posters in general.

[nevgee]

This is basic commissioning knowledge. If you want to get into the design then we can go there but I think that would be unnecessary considering the scope of practicalities here.

Gary asked about the bypass factor principles I mentioned - not the original poster. So the answers were not addressed to the original poster - only to Gary. The comments about this being a fresh air application possibly being asked to operate out of range were aimed at the original poster and all other posters in general.

Going into the design principles would be ok for me and probably be more helpful, hence my reasoning over the style and build of the coil block. I couldn't see how bypass factors could have anything to do with basic commissioning! They are elements of design not commissioning. I doubt there are many peeps on here who would have the experience of designing air coils from basics, without a pc at hand.

I wasn't having a go at anyone ... just pointing out the main thread.

[DTLarca]

Going into the design principles would be ok for me and probably be more helpful, hence my reasoning over the style and build of the coil block. I couldn't see how bypass factors could have anything to do with basic commissioning! They are elements of design not commissioning. I doubt there are many peeps on here who would have the experience of designing air coils from basics, without a pc at hand.

I wasn't having a go at anyone ... just pointing out the main thread.

No worries - but commissioning engineers must get the right SHR at the right total duty. For this they must understand the relationship between ADP and BPF. This is for custom build AHU's. For catalog AHU's only external static pressure and distribution balance is of concern. Standard AHU's have fans, motors and pulleys closely selected without much tolerance. Custom build AHU's these days have motors oversized by perhaps 40% with VFD's for RPM fine tuning according to ADP, SHR and BPF.

[nevgee]

No worries - but commissioning engineers must get the right SHR at the right total duty. For this they must understand the relationship between ADP and BPF. This is for custom build AHU's. For catalog AHU's only external static pressure and distribution balance is of concern. Standard AHU's have fans, motors and pulleys closely selected without much tolerance. Custom build AHU's these days have motors oversized by perhaps 40% with VFD's for RPM fine tuning according to ADP, SHR and BPF.

Sensible Heat Ratio is preset at design given specific design parameters. Aparatus Dew Point and ByPass Factors are also predefined at design. I can't see how a commissioning Engineer is able to make any corrections to these factors when he is most like never to achieve designg conditions at all. I would find it very unusual that any one would have the luxury and satisfaction of designing an AHU system with ducting etc and for it to drop into a design performance for commissioning purposes. In a real world it never happens. There are many peeps who sit at their drwng brds believing that the world is perfectly round ...well it surely isn't and never will be. There is a great difference between design practice and the realms of commissioning and the reality of having to instal a system that wasn't thought thru properly.

[DTLarca]

Sensible Heat Ratio is preset at design given specific design parameters. Aparatus Dew Point and ByPass Factors are also predefined at design. I can't see how a commissioning Engineer is able to make any corrections to these factors when he is most like never to achieve designg conditions at all. I would find it very unusual that any one would have the luxury and satisfaction of designing an AHU system with ducting etc and for it to drop into a design performance for commissioning purposes. In a real world it never happens. There are many peeps who sit at their drwng brds believing that the world is perfectly round ...well it surely isn't and never will be. There is a great difference between design practice and the realms of commissioning and the reality of having to instal a system that wasn't thought thru properly.

Nevgee, if you and I were standing in front of an ahu that was not achieving the correct SHR, say the SHR was too high, what would be on your short list of things to check or adjust if you were about to turn around and give me suggestions?

[Gary]

Nevgee, if you and I were standing in front of an ahu that was not achieving the correct SHR, say the SHR was too high, what would be on your short list of things to check or adjust if you were about to turn around and give me suggestions?

Is there a neon sign on the side of the AHU that says, "My SHR is too high"?

[DTLarca]

Is there a neon sign on the side of the AHU that says, "My SHR is too high"?

Pretty much though actually a mini LCD indication

[DTLarca]

Is there a neon sign on the side of the AHU that says, "My SHR is too high"?

Consider it this way, Gary.

You are standing between two AHU's. One has a return of 22 and a supply of 12 while the other a return of 24 and a supply of 21.

For a given deviation in leaving air temperature from design by say 0.2K which one is further off the SHR mark? The answer comes to mind instantaneously - yes?

[nevgee]

Nevgee, if you and I were standing in front of an ahu that was not achieving the correct SHR, say the SHR was too high, what would be on your short list of things to check or adjust if you were about to turn around and give me suggestions?

You buying coffee or me?