Unless I goofed up the math, your HX is running at less than 60% efficiency. That stinks for a plate HX and if true, is probably a big source of any flow trouble.
I'd check the PD across across various wshp's (and compare to mfg lit), tear down the HX & clean, then recheck PD's at the HP's.
If your heat exchanger is sized appropriately, your approach temperature is jacked all up, meaning you are not getting a good thermal exchange. My suspicion is two fold...
You should have a very very low pressure drop on your closed loop (condenser side) and potentially a slightly higher pressure drop across the tower side...Your leaving water from the exchanger to the building should be within a degree or so from the leaving water from the exchanger to the tower.....
That being said, it also sounds like you may have a piping issue, if the closed loop leaves the heat exchanger (assuming plate and frame type) from the bottom, then the tower side needs to leave from the top, this is called "counter flow". Personally I would get a qualified water treatment technician to put the system on Ph control and monitor how much acid it takes to control the Ph, if it takes very little, I would say you are in good shape, if it requires constant feed, then there you go..
Does your heat exchanger have a serviceable fitting at the plate? can you pull it apart and inspect the condition of the entering side of the plates? There is a possibility that it is full of debris (you would be amazed what can get stuck in there)...
Here is a picture of one that had a giant temperature split on the tower side and almost no split on the closed side (keep in mind that this is one of five 1200 ton exchangers on eight 900 ton towers).
Whatever you do, don't take it apart until you know what your cleaning....If they are scaled up, they will need to be acid washed, probably off site...(read;$$$$$$$$$$$$).
Get some more data...I am very familiar with this type of system.
Thank you for the information, I really appreciate it.
Originally Posted by GT Jets
The picture you provided, I am assuming that picture was taken just inside the heat exchanger tubing looking down the plates? The ... rocks are trapped between the plates?
We have an old SWEP heat exchanger, here is the info on the tag:
Make - SWEP
Model - G75.6
Apparently, SWEP was partially bought out or something during the manufacture of this model. We are currently trying to chase parts for it, getting a gasket kit and possibly some more plates to add some more capacity.
I have gathered some more data, and found a couple additional areas of concern. We have some areas we think the piping that was installed is too small causing the heat pumps to not get enough water flow.
I have a logging temperature meter I am using to log the temperatures of various parts of the system over 24 hours. I have the data for the temperature of the return water, from the building right before the heat exchanger.
As soon as I gather some more data I will put it on this post for everyone to see and review.
Right now, my meter is logging the temperature of the water after the heat exchanger entering the building. I will pull the data tomorrow morning and then hook it up to the water leaving one of our troublesome heat pumps.
You mentioned being carefull cleaning heat exchanger, can you elaborate? Whats the problem? Does the rubber gaskets not re-seal well? Difficult to remove the scaling? Could you explain a bit more?
I suspect we have ... a couple of problems with our system:
Not enough water flow to some of the heat pumps, caused by possible scaling inside the heat pumps and possibly pipes that are not big enough to carry enough water to the heat pumps.
Our heat exchanger, I don't think is working up to specifications. I keep getting different answers the temperature losses we should see across the exchanger.
We also have plastic pipes to carry the coolant throughout the building, that are going to burst on us sooner or later.
We don't have enough instrumentation in our mechanical room to properly diagnosis what is happening. We have a couple temperature gauges and two pressure gauges, that is it. We don't have any fittings on the pumps to hook up a gauge and determine how much pressure there is on each side of the pumps.
And finally, I have yet to determine if we possibly have air in our system.
Again, thank you everyone for the comments.
The reason I say don't pull it apart unless you know what your cleaning is because if it is scale that is mostly comprised of calcium carbonate your are very lucky and this can be cleaned with a simple acid wash, Rydlime works OK but a bit expensive IMHO..If your scale is comprised of silica, you are going to be somewhat screwed....
Originally Posted by richard.bessey
The picture I attached was from yesterday and yes, that was the entering side of the Tower side (open loop) and your looking in a 12" pipe.... 8 hours and about 100# of powdered acid later and she runs like new....:yes:
And just think, only four more to do.....:Faint:
Would it be possible for you to snap a picture of the heat exchanger?
Also, as for obtaining the gaskets, I would order a plate pack with about 20% more plates if you can swing it.... You better look at the torquing sequence on these before you attempt to pull it apart. They make some very special tools for this, yours is a baby, but still may consider calling in the experts....The ones we were working on were 9' tall and it takes about 10 hours to get them apart......No bueno...
SWEP now specializes in brazed frame exchangers, but they are still around.....Many manufacturers can hook you up with plates, your tag denotes 316 stainless steel...Pretty normal. Something free to check, wont take too long to do would be to isolate the open side and drain it, then close the valves back off and watch for the pressures to equalize, this would show you have a leaking plate internally and she would need to come apart no matter what....
Good luck my friend.
Tomorrow, I will get a picture of the heat exchanger and provide some data
As promised, here is the data and some pictures.
I have collected 24 hours worth of data, my meter recorded the temperature every 30 seconds for 24 hours. Then I downloaded the data into excel.
Here is the excel file with all of the data herehttp://richardbessey.com/test/hvac/comparison_data.xlsx
Graph of the water temperature coming from the building:
Graph of the water temperature going to the building (After the heat exchanger)
And finally a picture of our heat exchanger
The blue pump at the bottom of the heat exchanger is just sitting on the floor, its not hooked up to anything.
The two green taco pumps on the left are for the cooling tower. The two pumps on the far right of the picture that are cut off are the pumps for the boilers.
And there are two 5 HP pumps (not pictured) that run the main loop.
The barrel and the little yellow pump to the right of the heat exchanger is the biocide that is fed to the cooling tower.
Making some huge assumptions here....
You are only running one tower pump and one loop pump at a time correct?
I am going to go with the heat exchanger being fouled and potentially full of debris, particles larger than about 1/32" can get lodged in the plates and plug things up pretty solid.
Did you verify that the water flows are counter? Meaning the coldest tower water entering heat exchanger) is in contact with the coldest building water (leaving the heat exchanger)?
Correct, we only run one tower pump and one loop pump at a time. We have two pumps for redundancy.
Yes, I verified the cold water from the tower is coming in and is plumbed up to the exchanger correctly.
I was able to take a picture of one of the old pipes on our main loop that was removed during our re-model
Start that thing on Ph control yesterday..........JMHO.
Originally Posted by richard.bessey
Please note - there is build up like this on the steel pipe (Its a 6 inch nipple) but no build up on the plastic pipe at all (90% of the pipe is plastic)
I am afraid the inside of our condensers on our heat pumps might look like this though.
Got a pic of the plastic piping?