BMS Retrofit payback

[Loumolito]

Does anyone know a rough payback to retrofit an existing pneumatic control system with a new DDC BMS system? The building is a water treatment plant with offices, lab, maintenance, etc approximately 10,000SF. The building has a central hot water heating system with cast iron boilers. There are multizone air handlers with hot water coils (I am replacing with VFD AHU's & VAV boxes) and DX cooling.

 

[QualityTime]

I just finished off replacing a 30 year old pneumatic system in a water treatment plant in Toronto. It had 780 points throughout. The wiring standards and control panel standards that the City wanted were as if it were PLC controllers being used. We did not use EMT conduit and pressed steel boxes. It was TECK cable with water tight fittings and cast boxes. We prepared drawings showing each system. We showed the points that we wanted in typical ISA format for each system and we prepared corresponding wiring diagrams. We also gave them control architecture drawings showing what equipment belonged to each control panel. In the administration area we did not have VAV boxes we had constant volume boxes. All of the control panels throughout the plant talked to each other via a spare fibre optic line that was previously installed throughout the plant. The project went well. It was a Johnson Control system that was installed

I am in the process of having another contractor retrofit another City of Toronto water plant as we speak. That plant has 550 points and it is a Johnson control system that is going in there also

From my experience working in the US if it costs $100 Canadian to do the job in Toronto it will cost $100 USD to do the job in the US

 

[JVKS]

are you asking for the savings for just the portion of converting from pneumatic to DDC or the pneumatics to ddc along with the VSD, VAV, DX?

just a pneumatic to DDC conversion based on energy payback alone is long(15 to 20 years if not longer) and difficult to calculate. there are lots of good reasons to convert from pneumatic to DDC but even with advanced control strategies and tighter temperature control the senergy savings alone does not justify it. What I am finding though is the cost to correctly recalibrate/repair the pneumatics to get them working again is 1/2 to 2/3 of the cost to just replace with DDC depending how many and how bad the pneumatics are(dual duct boxes vs single zone, is there oil/water in the system, etc.)

if you look at doing the VSD, VAV and DX along with conversion to DDC controls(ddc is the only way to go) it will be a much better payback than having to break out the DDC controls seperately.

A VAV conversion on a 10,000 cfm air handler in a waste treatement plant that has long operating hours will most likely have a "decent" payback. with out more info it would be silly of me to SWAG a payback in years.

 

[EnergyProfessional]

From my experience some old pneumatic systems just don't work anymore and no one knows how to operate them. Spare parts are hard to come by too. If that is the case, the savings in both energy and maintenance are huge.
Obviously you want to do DDC as smart as possible to get most savings. Scheduling, water temperature setback etc. All the things you never could do with a dumb pneumatic system.

Occupant comfort is another benefit. Just tell the building owner what the annual salaries of the employees are and how much they could when they have better temperatures.

 

[QualityTime]

I concur with HerrKaLuen. There are fewer and fewer people around that know how to trouble shoot pneumatic systems and the parts are hard to come by and confusing to set up. In my case, we have a plant full of electricians and millwrights but they had to call in a contractor when things got really out of wack. Nobody knew exactly what they did to fix it,...if it ever was fixed. With DDC controls you can watch on the screen what is happening and reprogram things if necessary. Now the electricians understand what is going on and can fix any problems which come up. The other problem with pnuematic systems is that you have to have really dry clean air. If you don't things get plugged and your control goes out of wack.

 

[JVKS]

Yep when the current generation of fitters that has worked on pneumatics retires there will be systems out there that few understand(includng a few i designed)

Having said that there are good reasons pneumatics has gone bye-bye. decrease in installation costs, increased reliability, younger operators familiar with computers, better temperature control, easier trouble shooting all make DDC the way to go. once you have a DDC system it is difficult to go back to pneumatics.

havings oil or water in your system even once can cause problems for years. I still see no air dryers, shop air compressors(to much oil), water filters full of water.

Occupant comfort is a great benefit of DDC. the problem is that occupant comfort sometimte comes at increase energy costs. thermostas that are totally our of whack, pneumatic dual duct boxes that die between heating and cooling so the temp is ok some of the time, , closed OA dampers, cooling discharge air temps at 65 F when improved with DDC(or recalibrated pneumatics) add up to increased energy costs.

sorry just don't automatically fall into the just change to DDC and you will save lots of energy.

 

[EnergyProfessional]

just the possibility of remote control. i can sit at home and respond and fine tune the system without ever going on site. From home or my office i can talk to the controls contractor who is in his office and we never need to go on site to improve an algorithm.

 

[cjw81]

One place to start is to realize just how inefficient it is to produce compressed air. One seminar that I attended claimed that making compressed air for operating dampers and controls is about 10% efficient. Yes that means 90% inefficient. Having been involved with HVAC (mostly in healthcare) I would tend to agree with that percent. Just finding the leaks can be a nightmare.
I am looking into a green project of that nature (New York City area)but wold advise you to be careful in this area concerning national and local fire code. Most dampers (in my field) are used for fire or fire smoke applications. Make sure you replace any system with code compliant equipment. All systems for control also utilize default "on" position for your heating applications to prevent freezing in the event of air failure.










































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[mauricestoker]

Being a water treatment plant, have you considered water source heat pumps? Don't know what type of filter beds you have, but that could be one source already pumped. A HX on the incoming waer might be able to save cooling and heating.

I would not discount electronic analog if this is a standalone facility. It would be a lower upfront cost.

The EPA EnergyStar Building Manual-Stage 2 Building Tune-Up gives some rules of thumb; as it is generic, the numbers can be fudged toward the results you want.

 

[Loumolito]

Mauricestoker,

Interesting you mentioned geothermal heat pumps. I have another new plant where we are trying this design for the first time. Did you use a shell and tube HX or plate frame?

Are there any known DEP issues with using water supply for hvac? Lastly, did your condenser loop have glycol? I'm in the northeast we always use antifreeze in geothermal systems.

in the winter I think we will need supplemental heat when the water is 40F.

Your comments?