Why register? ...To Enhance Your Experience
+ Reply to Thread
Results 1 to 12 of 12

Thread: Heat Exchanger

  1. #1
    Forum Member
    Join Date
    Mar 2006
    Posts
    32

    Default Heat Exchanger

    Our first out engine has, at the engineer's controls, a lever for the heat exchanger. No one at the station seems to know what it is for. My best guess is that it is a heat exchanger between cold intake water (from a tank or hydrant) and hot engine coolant, that adds supplemental cooling to the engine when stationary and pumping on hot days. Is that correct? If not, what is it?


  2. #2
    Forum Member
    Join Date
    Jul 2004
    Location
    Penn Valley, Ca
    Posts
    571

    Default

    Can't say for sure without seeing it but that is generally how it works. Some are more effective than others.

    Birken

  3. #3
    MembersZone Subscriber
    Join Date
    Jan 2001
    Posts
    466

    Default

    This was out of the specs on our truck

    A heat exchanger shall be provided on the chassis cooling system. The heat exchanger shall not allow mixing of the chassis coolant and water from the fire pump.

    A gated discharge line shall be installed to provide water from the fire pump to the chassis heat exchanger to assist in engine cooling during pumping operations. The heat exchanger line shall be controlled at the pump operator's panel.

  4. #4
    MembersZone Subscriber
    Join Date
    Sep 2005
    Location
    So of Can. / N. of Mexico
    Posts
    869

    Default heat exchanger

    NFPA 1901 section 16.3.5 requires a supplementary heat exchanger to cool the engine when pumping. The pump water and engine coolent circulates through the heat exchanger through seperate lines and do not intermix. There should be a valve to control pump water going to the heat exchanger and a drain valve on the pump panel to drain pump water out of the heat exchanger.

  5. #5
    MembersZone Subscriber
    Join Date
    Feb 2005
    Location
    Asheville, North Carolina, United States of America
    Posts
    126

    Exclamation Use with care.

    The heat exchanger is to prevent to engine from overheating and seizing if there is a failure of the cooling system hose lines circulating the coolant through the engine block. It is designed for emergency use only, and should only be used long enough to get hose crews OUT of a structure should the cooling system fail during a fire attack, and then shut the engine down fast. If you use it on a "routine basis" as some departments are in a habit of doing, you stand the risk of keeping the engine below it's engineered designed operating temperature (which is what the thermostat is for), which in turn will not give you full rated horsepwoer, and in turn will reduce pump efficiency. If your motor is overheating during normal operations, check your coolant level, or get it checked by a mechanic, as even on the hottest of days it should not routinely overheat unless there is a problem with the coolant leval, a blockage somewhere in the system, or a bad thermostat.
    Pray for the dead, fight like hell for the living! - Mother Jones

  6. #6
    Forum Member
    Join Date
    Jul 2004
    Location
    Penn Valley, Ca
    Posts
    571

    Default

    Most heat exchangers are plumbed after the thermostat so they can't overcool the engine but some are plumbed to heater hoses, however I always run with them open no matter what and they definitely cannot overcool the engine no matter how they are plumbed, they are only 2- 1/4" tubes running to them after all. I agree that they "should" not be necessary to keep the engine cool and for the most part aren't but one of our POS engines it is, and there's nothing I can do about it but it has never caused a problem in operation either.

    Birken

  7. #7
    Forum Member
    Join Date
    May 2006
    Location
    Bryn Athyn, Pa.
    Posts
    1,618

    Default

    [QUOTE=herbroberson]"The heat exchanger is to prevent to engine from overheating and seizing if there is a failure of the cooling system hose lines circulating the coolant through the engine block. It is designed for emergency use only, and should only be used long enough to get hose crews OUT of a structure should the cooling system fail during a fire attack, and then shut the engine down fast."

    I think herbroberson is equating the heat exchanger, or Auxiliary Cooler with the old "Emergency Cooler." In the event of a failure of a cooling line, the heat exchanger will not do any good, because it does not add anything to the cooling system.

    Emergency Coolers, on the other hand, took some of the water that was being pumped and diverted it to the engine's cooling system. Many an engine has been ruined by them, because what was being pumped, especially from draft, contained silt, mud or whatever. If it wasn't immediately drained, the stuff would settle in the engine's cooling passages and block them. Emergency Coolers were used years ago before permanent anti-freeze and pressurized cooling systems became commonplace. It wasn't unusual for the engine's cooling water to evaporate or boil out. You opened the emergency cooler and refilled the radiator so that you could continue pumping. I haven't seen one in many years.

    Auxiliary coolers, on the other hand, merely increase the cooling capacity of the system by supplementing the radiator. A water to coolant heat exchanger is added, frequently but not always in the upper radiator hose. The cooling medium for the heat exchanger is the water being pumped rather than the air being pulled through the radiator. The water being pumped is not added to the vehicle's cooling system, it just cools the exchanger coils and is returned to the intake side of the pump.

    Remember that our vehicle engine and its systems are designed to operate with the vehicle in motion. In addition to the fan, "ram air," or air being pushed through the radiator by the forward motion of the vehicle is a big part of the overall cooling system equation. When we park the vehicle and put it into pump mode, we've turned it into a stationary engine. Under conditions of hard pumping and/or high ambient temperature, sometimes the air being pulled through the radiator just isn't enough to do the job. Enter the auxiliary cooler.

    I quite agree with Birken that the thermostat will still properly regulate the engine temperature. Where you see low coolant temperature is usually when there isn't sufficient load against the engine to generate enough heat to open the thermostat. Even if the auxiliary cooler is left open, the flow of coolant in the engine is still being limited by the position (open, closed or in between) of the thermostat. However, the thermostat bypass passage will continue to pass a small amount of cooler coolant, so I prefer to leave the auxiliary cooler closed, and open it if needed.

    Stay safe out there, everyone goes home!
    Last edited by chiefengineer11; 08-03-2006 at 06:40 AM. Reason: Syntax and clarifications

  8. #8
    MembersZone Subscriber
    Join Date
    Sep 2005
    Location
    So of Can. / N. of Mexico
    Posts
    869

    Default aux cooler

    Chiefengineer is correct.
    Most commercial chassis cooling systems are designed with a 30% duty cycle, meaning they are sitting stationary for 30% of the time and moving 70% of the time with ram air through the radiator. So I'm told by my Navistar dealer friend.
    They aren't designed to be pulling full engine horsepower in a stationary position. So the requirement by NFPA for an auxilary cooler to increase cooling capacity during pumping operations.

    This is probably one of the differences between a commercial chassis and a purpose built custom pumper chassis. Most customs are probably designed with enough radiator capacity to pump maximum horsepower in a stationary position.

  9. #9
    Forum Member
    Join Date
    May 2006
    Location
    Bryn Athyn, Pa.
    Posts
    1,618

    Default

    Donethat's point with respect to cooling systems and commercial vs. custom is well taken. I mentioned in a different thread that I'm part of a focus group that International Truck & Engine Corp. has put together to help them better understand the needs of the emergency services (even though we don't have any Internationals). I'll forward some of these on to them, and bring it up at our next meeting (probably following FDSOA next January, in Orlando).

    Stay safe out there, everyone goes home!

  10. #10
    Forum Member
    Join Date
    Jul 2004
    Location
    Penn Valley, Ca
    Posts
    571

    Default

    My experience with cooling on custom vs commercial has been the opposite. In my experience commercial conventionals keep cool much easier than cabovers. In a conventional the air flow is much less restricted. It doesn't take a rocket scientist to figure this out. Just look at the grille of your favorite truck and how much room there is to suck air in there. My big Pierce Lance on the other hand with its giant grille has no problem keeping cool. The above were only generalizations and you have to consider things on a case by case basis. But I would build into any spec that the engine be able to pass pump test on a hundred degree day without exceeding x degrees water temperature. Look in the book of the motor manufacturer for the figure. 235 maybe IIRC. Also specify that the aux cooler be plumbed with say 1/2" lines instead of the usual 3/8" or 1/4" so when you do open it, it really does something.

    Notwithstanding the above, I always run with my aux coolers open out of the barn, that way I do not forget when I get to the fire ground, or am away from the engine while it's pumping. It certainly can't hurt anything, and may save the cost of an engine overhaul or even a brother's life, even if you never know about it. I just like to give myself every edge I can.

    Birken

  11. #11
    Forum Member
    Join Date
    May 2006
    Location
    Bryn Athyn, Pa.
    Posts
    1,618

    Default Response from International

    I copied and sent sme of the posts to Bob Neitzel, Emergency Services Marketing Manager at International Truck & Engine Co. Got the following back from him this morning:


    "Actually everybody is correct if you look at everything that has been produced. The auxiliary cooler was added because in certain circumstances the standard truck cooling system could not drive enough heat off and the engine would damage itself. Thus the auxiliary was created to help out the engine. Two basic kinds of water coolers, one an “open system” that circulates the source water into the engine block. The open system works well for a while but it is bad for the engine as it flushes the coolant out of the engine and introduces a potentially “dirty” water into the engine. An open system depending on your vehicle will either flush out green coolant that has been treated w/SCA or new red coolant that is the long life coolant now used by all the OEMs. I think it’s worse than not having a cooler, all sorts of junk and rust gets in the engine. This is a certain path to damage. On the new hot diesel NEVER put anything but coolant with proper water treatment in. The second type is a “closed system”. The source water goes through a cooler that has the engine cooling water in it. The source and engine water never mix. This is a good system more often used in Marine diesels.

    The modern electronic diesel runs much higher water and oil temperatures than years ago. The newer diesels have a cooling system that circulates quite a lot of water in the engine with the thermostat closed. (older engines circulated little or no water with thermostat closed). Even the engine oil has a thermostat before going to a cooler. Our oil thermostat opens at 230 degrees F and water begins to open at 205 degrees F. These temperatures, seemingly high, are required to maintain emissions and performance. Even the engine brake has a temperature component that prevents the potential stall at too low water temperature. No matter the type, size, or number of auxiliary coolers have been added, the engine thermostats rules, and it will maintain the engine temperature. The big reason for this discussion is that the new diesels run hotter than previous and many people are unfamiliar. An auxiliary cooler can’t over cool an International diesel, the engine thermostat will see to that. Adding a cooler will not lower the engine operating temperature, the thermostat will see to that.

    Every O.E.M. chassis manufacturer has their own standards of “air to boil” radiator performance. So I can’t speak for anybody else. Our heat exchange systems are design to operate at 100% rated HP engine load heat rejection, 0 MPH, and maximum air temp 115 degrees F. Do we make exceptions for certain application so they can have higher HPs? Yes we have, mostly highway tractor that have the gift of ram air, but not in Fire/Rescue applications.

    Now having said the above, the introduction of more EGR into the 2007 engine requires more heat to be pulled out and used to cool the exhaust gases in the EGR, hence the larger radiators coming to handle this additional heat source.

    Up until 2007, we could assume that the maximum heat rejection load was at rated RPM, so we gained some help from a fast spinning fan, fast water circulation, and maybe ram air. In 2007 the maximum heat reject load will come at “Full EGR”. That may occur at zero MPH, no load, idle…no ram air, no big fan rpm, no rapid water circulation. The cooling system components and fan are now 25%+ larger. The 2007 engines should be able to accommodate any heat load without an auxiliary cooler. We can work with Engineering for clarification. If you are running a load at pumping speed, EGR should not happen.

    Many features of the electronic diesel work to protect the engine from loss of mission or internal damage. Such as timing changes, fuel de-rating, control engine fan, and turning off loads such as A/C compressor. In addition most will sound alarms and flashing lights to warn the operator long before shutdown will occur. The only thing I can think of that could cause a sudden shut down would be complete loss of electrical power like a battery master, switched off. I think we should ask the engine engineers first. But if my understanding of EGR heat loading is correct an auxiliary cooler may not be needed on an apparatus with a 2007 diesel engine.

    Would it hurt to add an auxiliary cooler to a 2007 EGR diesel? No. I doubt it would get much use since the engine could bypass it on a regular basis. And when it might call for help say at idle, because of flow and RPM, the auxiliary cooler may not have much thermal effect. The question then becomes, could you better use the space, money and weight savings of removing the auxiliary cooler?"

    Let me know what other questions you may have.

    Thanks,
    Bob Neitzel
    Call me if you have question 630-753-3851

    Stay safe out there, everyone goes home!

  12. #12
    Forum Member
    Join Date
    Jul 2004
    Location
    Penn Valley, Ca
    Posts
    571

    Default

    I don't fully agree with all of the above:

    1. Not all heat exchanger coolers are plumbed in the radiator top hose, after the thermostat. I have some that are basically mounted on the side of the engine, in continuous engine circulating coolant, not regulated by the thermostat. However they do not have the capacity to over cool the engine under normal circumstances. They are an adjunct, not a radiator in themselves. But they do work.

    2. All of the diesel engines I have worked on, old and new, have pretty much full flow bypass when the thermostat is closed in the cold position.

    3. EGR was introduced in 2002, on International and everybody else's engines. (Cat is debatable.)

    4. The water-to-water heat exchanger has nothing to do with EGR. It simply pre-cools the water going to the radiator. It does not care what the source of the heat was, whether it was the engine liners or the EGR cooler. So it works any time there is water flow through the radiator. If the thermostat is shut then the engine is below operating temperature and needs no cooling.

    Birken

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Ooohhh I Can Just Feel The Heat Now
    By MalahatTwo7 in forum The Off Duty Forums
    Replies: 0
    Last Post: 03-30-2006, 03:09 PM
  2. All SCBA's to be obsolete in 2007?
    By ullrichk in forum Firefighters Forum
    Replies: 143
    Last Post: 11-01-2005, 07:39 PM
  3. Heat Tolerance
    By BruenRescue2003 in forum Firefighters Forum
    Replies: 19
    Last Post: 08-19-2004, 02:40 PM
  4. This Weeks Safety Message
    By MalahatTwo7 in forum Firefighters Forum
    Replies: 3
    Last Post: 08-04-2004, 06:49 AM
  5. Firefighters-Dealing with heat
    By NJFFSA16 in forum Wildland Firefighting
    Replies: 0
    Last Post: 07-23-2003, 11:35 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts