Problems about balancing pressure in hydronic HVAC systems

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Problems about balancing pressure in hydronic HVAC systems

Postby simoncons » Tue Sep 11, 2012 3:56 am

Hello
My name is Simon and I am working as a consultant.
I am looking into problems about balancing the pressure in hydronic HVAC systems. I am interested in knowing, if this is a familiar problem for you (e.g. happens in 8 out of 10 installations) and how you usually solve this?
I have a case where a five star hotel repetevely have to pay back the room rent to unsatisfied guests because the hydronic system is not balanced and not able to distribute the cooling water to the far end of the building. Unsatisfied guests, unsatisfied hotel owner, unsatisfied technical manager.... Several things have been tried out including installing a bigger pump and chiller without success?


I had one of our illustrators make the case story into a little "comic", just to illustrate the -
*.us/photo/my-images/716/hotelhd.jpg/
simoncons
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- Problems about balancing pressure in hydronic HVAC syste

Postby juster » Tue Sep 11, 2012 11:05 pm

Is this a new installation?
If so, was the hydronic system cleaned before chilled water was introduced?
If new you should have a balancing report and and use it to trouble shoot. Can call the engineer who designed it to recheck the work.
What are the controls in the local rooms? If a new installation most likely, electronic. If this is an older building then it could be pneumatic. In ether case, are these controls operating correctly? Are signals getting to the control devices?
If you believe there is a balancing problem, then call a balancer to check pressures in different areas. Start at the pumps and work your way up through each floor.
If the problems are in certain areas then go to these areas to start your balancing checks.
Is this chilled water had good or any water treatment? Is it being filtered continually? Have a water treatment specialist check the chilled water to see if is in satisfactory condition. If not and you have a bacteria inside your cooling closed loop. This could cause the system and especially smaller pipes to clog up.
Are the cooling coils in each room, clean?
Is the building a multi-story building? if so are more of the cooling problems in the upper or lower parts of the building? Lower portions of the building may need flushing if the chilled water has not been maintained.
Do not continue changing parts until your problem is discovered.
If this is a new building, is the chilled water pump partially plugged?
If this is an older building has any work been done to the chilled water loop or chillers? Maybe someone introduced contaminants or debris into the piping?
Interesting story board, I would hope this is not a joke
juster
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- Problems about balancing pressure in hydronic HVAC syste

Postby simoncons » Mon Sep 17, 2012 3:02 am

Juster,

It's not a new installation, about 10 years old. The building is from arround 1900 and the hydronic system is retrofitted.

in more detail the installation looks like -
The system is a combined heating and cooling systems in a hotel. It has about 30 fan coils of 10.000 - 20.000 Btu (3-6kW) that cools the rooms in the summer and heats them in the winter time. The hydronic system is a two pipe system and the water to the fan coils are controlled by an thermostat in the room and an on/off coil valve.
The system works fine in heating mode but the cooling mode is crap... No cold water in the far end

A second contractor has been changing equipment, pump, chiller, buffer tank and installed a filter to clean the pipe system. Flushing and filtering has taken out a lot of derbis but not made the system work well enough. The contractor that installed the system is out of business.

The story board is not a joke. The intention is to show the problem that the failures in the hydronic system causes and I hope to get a discussion about how often hydronic systems fail. We need to find better solutions, the problem seams extremely complex from all the details that you need to be on top of to track down the source(s) of the problem.

Any idea who would be specialists or experts in this diagnostics work?
simoncons
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- Problems about balancing pressure in hydronic HVAC syste

Postby juster » Tue Sep 18, 2012 7:43 am

When you say "no water at far end" I am not sure what you mean. Is this a multistory building, or all on one or two floors? If this is a multistory building and you mean "far end" by the bottom, then the coils at the bottom my have collected debris and may need to be flushed. If this is building all on one floor then air may be trapped in the coils or both.
In any case do these cooling coils have air bleeders on them. They may have air trapped in them. If this is the case you will have no or very little flow. The air must be allowed to come out. Do you have air bleeders on each coil? if so , have they been bled?
Each cooling coil should also have a drain for flushing. This could be used for bleeding air as mentioned or used for flushing debris. Have the coils been flushed to ensure there is no debris? New systems are prone to having debris due to slag from welding or soldering.
Each coil should also have two isolation valves. By closing each one, (one at a time) you can flush debris or air.

With the building only retrofitted 10 years ago, you should have drawings from the engineering. Each of the chilled water coils should have been balanced. The balancing valve should be on the return water side. There should be a balancing report. If not you can contact a balancer to look at the system. All the coils will need to be checked one at a time.

Do you have a chemical treatment company? if not you should contact one to help you analyze the the chilled water. If you have not been treating the water and some of your chilled water piping is steel, you will have a problem as steel needs to have treatment in order to keep the reaction of corrosion in check. Debris from corroding inner piping will cause your water to become black and full of debris. It could get black and thick. I have seen this.
You should have a micron filter installed on your chilled water loop. A chemical treatment company will help you find the best place to install this. Usually hooked to the supply and return piping on ether side of the chilled water pump. The filter should be checked and replaced when needed.
If you do not have any steel piping debris can still be plugging your system in spots and require flushing. 30 units is not that many so flushing the entire system should not be a problem. Again a chemical treatment company can help you with this.

Controls, are the control valves opening and closing properly?
What kind of controls do you have? pneumatic or electric? have they been checked for proper operation? If pneumatic do you have proper air pressure all they way through your system? Do you have an air dryer on your pneumatic system? if not you could have water trapped in your pneumatic system causing your controls to not function. Electric valves could not be receiving a signal and be operating intermittently. Have your controls person check these.

Control valves for the main chilled water system, do you have any? are they working properly?

I would assume you should have tried most of these options before changing a pump or a chiller. They would be the last things to change.

Hope some of this helps
let me know
juster
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