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Emmett
01-09-2011, 01:36 PM
I have a enviornmental test chamber in which engines are tested, so the system was fitted with a dry air makeup system to provide combustion air, however when it was sized the company appearantly did not account for post cooling coil and so we can only just barely use it or we cannot maintain temperature in the space. Since we cannot use the dry air makeup system as we wish we ultimately invite wet, hot air into the space causing the coils to freeze up. Now here is the good part, the company who installed said there would be no need for defrost as they had fitted the system with a dry air purge system, I insisted they install some amount of heat for "potential" defrost but it just cannot do an effective job of removing all of the moisture and in the end we have iced up coil. The question I am posing to all is where should we invest our time? Providing a post cool coil so that we can use the dry air system at will, which in theory should allow us to run with very limited if any defrost requirements or invest in providing the proper heat in the proper place to defrost the coil? by the way the second option requires a new style evaporator as we want to put the heat in it.

chillerman2006
01-09-2011, 01:54 PM
Hi Emmet

I would be inclined to scrub & dehum the intake air, then your room coils can control temp easily.

I wonder why your looking to test engines with dry air though, would it not be more realistic to test with what ever comes in ? Giving you a more real world idea from your tests, than air that is only available normally during frosty winter months, the other thing during winter to consider is air mass increases with low temps, turbo cars love it, if your dehuming then heating, your air mass is low & dry, not sure that applys to real world conditions,(maybe sahara) but then I am just mr nuts & bolts so maybe wrong ! Again

R's chillerman

Emmett
01-09-2011, 03:03 PM
Hi Emmet

I would be inclined to scrub & dehum the intake air, then your room coils can control temp easily.

I wonder why your looking to test engines with dry air though, would it not be more realistic to test with what ever comes in ? Giving you a more real world idea from your tests, than air that is only available normally during frosty winter months, the other thing during winter to consider is air mass increases with low temps, turbo cars love it, if your dehuming then heating, your air mass is low & dry, not sure that applys to real world conditions,(maybe sahara) but then I am just mr nuts & bolts so maybe wrong ! Again

R's chillerman

all tests in this space are designed to be winter conditions only and typically only a starting test, the engine only runs for a few minutes at a time, we do not actually inject the air into the engine but make up the air in the room. If I understand you correctly you are suggesting that we invest time into making the air drier work as advertised?

chillerman2006
01-09-2011, 03:49 PM
all tests in this space are designed to be winter conditions only and typically only a starting test, the engine only runs for a few minutes at a time, we do not actually inject the air into the engine but make up the air in the room. If I understand you correctly you are suggesting that we invest time into making the air drier work as advertised?

what i was refering to is just a personal preference over rooftop ahu's that condition the air entering the lab over multiple small ahu's in the lab(I may have miss-understood your setup) also if looking at winter conditions, air inlet to engine's intake needs to be of low temp to have the same mass as on a winters day, as you & i have said air also needs to be dry...the bit that I could not confirm from the post was if the air you are looking for is low temp & dry or higher temp & dry, the first being an accurate resemblance of a winter day, the latter of only hot dry area's such as deserts, we are all from different fields of the industry here and some experiences cross over and some do not, was just looking to see if mine could assist yours, as also interested as a bit of a part time motorhead

R's chillerman

Emmett
01-09-2011, 04:11 PM
Chillerman2006

Sorry I wasn't clear about the room, it is a cold temperature test chamber, typical test point's are 0 degc, -18degc, -32 deg c, and -40 deg c occasionally -55 deg c. The room has two AHU's each with two coils one we call high temp and it uses R404A to maintain the room temperature at the 0 and - 18 deg c temperatures, the other coil is a cascade coil R508B and it is used for all other test temperatures. We rotate the ahu's, when one is in defrost the other cool's the room. The problem we have is the dry air make up unit provides air at around 20 deg c and - 80 dew point. The refrigeration systems can only handle this extra live load at 0 and - 18 deg c temperatures and is therefore usless at lower temperatures because we cannot maintain the temperature in the room with it running below - 18 c. Because we cannot run this make up air unit the engine draws air from the outdoors, what ever the ambient conditions are, we get it in the room, you can see how that would be an issue in july in the US (say 32 deg c and 70+ % humidity. The result from running the room at say - 32 deg c and sucking air from the outside into the room for combustion, is that the coils frost up quickly and the manufacturer did not provide adequate defrost heat to clear them. We are now looking at two options to rectify the situation.
(1) Install different evaporator coils with the ability to have imbedded heat rod's (the evap has additonal rows that are not used for refrigerant and you can install heat rods in them) or
(2) install a cascade post cool coil on the dry air make up unit which will allow us to run it through out any test cycle therfore reducing or "hopefully" eliminating the need to defrost.

chillerman2006
01-09-2011, 04:21 PM
Chillerman2006

Sorry I wasn't clear about the room, it is a cold temperature test chamber, typical test point's are 0 degc, -18degc, -32 deg c, and -40 deg c occasionally -55 deg c. The room has two AHU's each with two coils one we call high temp and it uses R404A to maintain the room temperature at the 0 and - 18 deg c temperatures, the other coil is a cascade coil R508B and it is used for all other test temperatures. We rotate the ahu's, when one is in defrost the other cool's the room. The problem we have is the dry air make up unit provides air at around 20 deg c and - 80 dew point. The refrigeration systems can only handle this extra live load at 0 and - 18 deg c temperatures and is therefore usless at lower temperatures because we cannot maintain the temperature in the room with it running below - 18 c. Because we cannot run this make up air unit the engine draws air from the outdoors, what ever the ambient conditions are, we get it in the room, you can see how that would be an issue in july in the US (say 32 deg c and 70+ % humidity. The result from running the room at say - 32 deg c and sucking air from the outside into the room for combustion, is that the coils frost up quickly and the manufacturer did not provide adequate defrost heat to clear them. We are now looking at two options to rectify the situation.
(1) Install different evaporator coils with the ability to have imbedded heat rod's (the evap has additonal rows that are not used for refrigerant and you can install heat rods in them) or
(2) install a cascade post cool coil on the dry air make up unit which will allow us to run it through out any test cycle therfore reducing or "hopefully" eliminating the need to defrost.

Hi Emmet

I am with you now....you can get coils that have a mixture of options that may assist...there are split coils that have two seperate liquid feeds...and ones with damper control for air flow...if you can source a coil setup that has both options...hopefully this would resolve your issue allowing one to defrost, whilst the other continues cooling...these are not something I have had to source before but I know they are available

hope this helps

R's chillerman

Gary
02-09-2011, 01:13 AM
Is there a minimum fresh air requirement?... and is the dry air unit set at the minimum?

mad fridgie
02-09-2011, 07:43 AM
If I understand right, your present 2 systems just recirculate the air in your chamber.
How ever when the engine is your exhaust, is vented external to the chamber, so you need to replace this combustive air (ie, 3L engine at 6000RPM = 18000L/M)
Your problem is 2 fold, one you can not maintain Very low temps due to the extra load.
Second the fresh air (moisture laden) freeze the coil and you do not have enough time defrost the coil.

Very simple question for does your system work in late Autumn, Early Spring and Winter. With no issues. (temps below 5C for example) If yes then a simple cooling system on the fresh air make up.

If not at what ambient does it work at.?

Emmett
02-09-2011, 01:22 PM
Is there a minimum fresh air requirement?... and is the dry air unit set at the minimum?


the requirement depends on the engine, (what will it consume). The make up air unit is fixed at 1200 cfm, 21 deg c discharge air temp and -80 deg c dew point. we test many different engine sizes, 1200 cfm covers about 90% of the engines we test.

Emmett
02-09-2011, 01:39 PM
If I understand right, your present 2 systems just recirculate the air in your chamber.
How ever when the engine is your exhaust, is vented external to the chamber, so you need to replace this combustive air (ie, 3L engine at 6000RPM = 18000L/M)
Your problem is 2 fold, one you can not maintain Very low temps due to the extra load.
Second the fresh air (moisture laden) freeze the coil and you do not have enough time defrost the coil.

Very simple question for does your system work in late Autumn, Early Spring and Winter. With no issues. (temps below 5C for example) If yes then a simple cooling system on the fresh air make up.

If not at what ambient does it work at.?

Mad,
All of what you have written is correct, the systems do recirculate, the engine exhaust is vented out of the space, and yes the problem is two fold as you describe, and yes again the system does run well in dry, cool conditions.

Why did I miss that!!!!! It makes perfect sense that if when we draw in dry cool ambient air the system works well that if we simply artificially provide that year round we will be ok. We had already gone down this path already and have a quote to add a cascade low temp post cool coil, however there is a camp of thought that says fix the defrost problem. I was seeking advice and opinions of which we should do, fix the defrost or add a post cool coil so that I had some answers for the man writing the check when asked why are we doing this and not that.
I appreciate your advice and am open to hearing from anyone else who has an opinion.

chillerman2006
02-09-2011, 03:13 PM
Reading back through 'As per normal Mad is on the ball' & looks like you need an increase in air flow to your chamber and to condition the air prior to entering the lab, but this gives you a second issue to be aware of, once you drop the rh below 40% it starts to become an uncomfortable environment to work in & much lower electrical equipment suffers from electro static discharge & can damage your equipment. This whole system needs carefully planning to take into account not only the engines requirements but also personel & electrical devices. There is not a quick fix as it would appear the original designers have not fully understood your requirements. Maybe your company would like to fly in either 'Mad' or 'Magoo' to sort this out for you once & for all. Both currently do projects internationaly that others fail to resolve !

R's chillerman

Gary
02-09-2011, 03:29 PM
I would start with taking a long hard look at the dry air system. Is it possible to lower the output temp and raise the dewpoint temp? Better to adjust the system than add to it.

chillerman2006
02-09-2011, 04:26 PM
May be you could find time to out from your well earned retirement Gary, to go and have a look & see what can be done, I know its a fair trip for you but this is a specialist setup, requireing a top techy to get it right, my suggestion of 'Mad' or 'Magoo' is based upon the fact that the original contractors that installed the equipment have not met Emmet's companies requirements, either by equipment selection or commissioning of the equipment and they most certainly will !

Gary
02-09-2011, 04:56 PM
It's a long drive... and I don't do airports.

chillerman2006
02-09-2011, 05:01 PM
Emmet...best speak to the boss and see if a winnibago complete with driver, can be supplied then with a fat pay cheque, you may be able to tempt Gary into this one ! ;)

Gary
02-09-2011, 05:14 PM
the requirement depends on the engine, (what will it consume). The make up air unit is fixed at 1200 cfm, 21 deg c discharge air temp and -80 deg c dew point. we test many different engine sizes, 1200 cfm covers about 90% of the engines we test.

How many CFM would it take to cover 100% of the engines you test?

Emmett
02-09-2011, 06:16 PM
I would start with taking a long hard look at the dry air system. Is it possible to lower the output temp and raise the dewpoint temp? Better to adjust the system than add to it.

Gary,
It is not possible to lower the output temp, the system is a regenerative dessicant drier, it has a precool coil which lowers the entering air temp down to 40 deg f then it passes through the dessicant wheel which has recently been exposed to hot air to dry it out, the output air off of the dessicant wheel is 70 deg f so the only way to lower this temperature would be to lower the precool evaporator coil temp which much lower and we will begin freezing the coil or add a post cool coil.
Why would I want to raise the dew point temperature? are you concerned with moisture infiltrating the space from every nook and cranny with the room so dry?
Also I have been spending a lot of time in your neck of the woods and will likely be making a move there next spring.

Emmett
02-09-2011, 06:20 PM
Emmet...best speak to the boss and see if a winnibago complete with driver, can be supplied then with a fat pay cheque, you may be able to tempt Gary into this one ! ;)

I'd be pleased to come and get him myself, love the area he lives in, does the satisfaction of knowing you were superman for a day count towards a fat check?

Emmett
02-09-2011, 06:21 PM
How many CFM would it take to cover 100% of the engines you test?

2200, this is a test rarely performed in the cold room.

chillerman2006
02-09-2011, 07:26 PM
I'd be pleased to come and get him myself, love the area he lives in, does the satisfaction of knowing you were superman for a day count towards a fat check?
miss understood....story of my life lately

Emmett
02-09-2011, 07:35 PM
I don't follow chillerman 2006, the superman comment was intended to intice Gary, ie sometimes being the hero is the reward itself, sorry if I offended you.

chillerman2006
02-09-2011, 07:40 PM
Sorry emmet

you caught me on the hop...up to my eyes at moment

gonna log off before I upset another

Gary
02-09-2011, 07:43 PM
2200, this is a test rarely performed in the cold room.

Just trying to get a feel for the requirements.

A solution which added another 1000 CFM of makeup air would not be amiss.

The low -80C dewpoint would be needed for the -55C testing, but not necessary for the warmer test points... and may in fact be unrealistic for these tests.

Gary
02-09-2011, 08:11 PM
I'm working on becoming supercouchpotato. It's not working out that well... I keep finding home improvement projects.

Gary
02-09-2011, 08:48 PM
The post cooling coil would be the easy fix. As to defrosting the room units, it is better if they don't frost to begin with.

Other solutions that come to mind would be very involved and very expensive.

mad fridgie
02-09-2011, 11:37 PM
So all you need to do is to quantify the cool/dry ambient air conditions when the system works well.
design a system to simulate these conditions. (there will be a bit of control required to meet the big variants in your ambient)
How is the fresh introduced, (negative pressure in the chamber, caused by the engine air intake) or (do you have some form of fan positive pressure in the chamber)

If the engine option, then you need to take into consideration the effect of engine capacity and air density at the low temps. (revert engine flow at -55C (mass flow) to worse case ambient conditions!

chillerman2006
03-09-2011, 01:48 AM
Hi Emmet

this thread you have started has had over 340 views in 24hours with only two of the sites top techs (discount me) replying due to the complexity of your requirements...Your company really needs an engineer at the higher level to resolve this...most I guarantee will not...you will be wise to contact 'Mad' direct & speak about availability to resolve this for you, once and for all...otherwise you will find it hard to get someone at that level, obviously they are about but can you lay your hands on them, I can not recommend anyone locally to you...will pm you some contact details & then its up to you & your company what you want to do

R's chillerman

mad fridgie
03-09-2011, 09:44 AM
If you use your peak figures, and chill the make up air to 5C 100% RH, you need approx 80Kw ambient air conditioner.
Do NOT get a price on a 80Kw chiller.

Josip
04-09-2011, 10:57 PM
Hi, mad fridgie :)


If I understand right, your present 2 systems just recirculate the air in your chamber.
How ever when the engine is your exhaust, is vented external to the chamber, so you need to replace this combustive air (ie, 3L engine at 6000RPM = 18000L/M)
Your problem is 2 fold, one you can not maintain Very low temps due to the extra load.
Second the fresh air (moisture laden) freeze the coil and you do not have enough time defrost the coil.

Very simple question for does your system work in late Autumn, Early Spring and Winter. With no issues. (temps below 5C for example) If yes then a simple cooling system on the fresh air make up.

If not at what ambient does it work at.?

I assume all tested engines are 4 strokes type .... 18000(L/M)/4= 4500(L/M) ....

and agree with the bold underlined sentence above ...


Best regards, Josip :)

mad fridgie
05-09-2011, 06:21 AM
Hi Josip,

2 strokes per rev, so 4 stroke would 50% of total swept volume (air drawn in every second rev), but These engines look a mighty size, so could well be 2 stroke diesel. A bit of a side issue.

cheers

Mad

Josip
05-09-2011, 09:53 AM
Hi, mad fridgie :)


Hi Josip,

2 strokes per rev, so 4 stroke would 50% of total swept volume (air drawn in every second rev), but These engines look a mighty size, so could well be 2 stroke diesel. A bit of a side issue.

cheers

Mad

Sorry, I miss 2 stroke .... that chamber is in USA and I assume 4 stroke engines between 2,5 L up to 6,0 L .... as per Emmett fresh inlet air 1200cfm up to 2200cfm ...

....anyhow can be solved with simple inlet air cooler ....

Best regards, Josip :)

Emmett
07-09-2011, 03:21 PM
Chillerman2006
Gary
Mad
Josip
Sorry I have been away from the forum for a few taking care of some personal business.
I would like to thank all of you for your comments and suggstions, just a little update. We do have several engineers working on this issue, however we had engineers working on the original upgrade and that did not work out as expected. I have some influence in my organization although I am just a techie not an engineer, so I wanted to get as much input from the experienced mind's on this forum before I provided my input into the situation. I feel very confident that attacking the issue from the air inlet (combustion air make up unit) is the right direction as several of you have pointed out if it works well under the right ambient conditions then it should work well if when you provide the appropriate make up air. This incidentally is the direction the engineers wanted to attack it from. So as it stands right now we are going to be adding a low temp post cool coil, and looking at controlling the volume of makeup air. I will provide an update as soon as one is available. Thanks again for all the comments I always learn when I ask questions.

mad fridgie
07-09-2011, 10:37 PM
You should consider a thermal storage unit (glycol) Size the air heat exchanger, to suit the maximum load conditions.
Calculate the total maximum daily energy required. (you indicated that actual run times are only for short periods)
Diversify your load of say a 18 hr period, and size thermal storage tank to suit. The refrigeration system becomes very simple and no need very fancy controls. The chilled glycol is pumped through the air heat ex changer and is controlled by a 3 port valve. This allows for easy control of the varying air flow and air temp conditions.
I would look at storing the glycol at -5C, use your 3 port valve to supply the air heat exchanger (coil) with 0C glycol. (no freezing of the coil) Design the coil with a low face velocity and i would also go for quite a deep coil, to ensure maximum moisture removal. Regardless of the load the air supplied will be at the desired result
When the storage tank warms the refrigeration clicks on, brings it back down and turns off. (load will determine run time)

A fool proof system.!