Old single line boiler\chiller system... 2

[SolutionsWanted]

I'm charged with making a 1960's HVAC system more efficient. I'm focusing on our 50,000 sq ft 2-story main building: 2-gas fired Hurst water tube boilers (3600 mbtu's each), 1-steam boiler, 2-rooftop chillers... but only 1 line for both heating and cooling. Because the system has been compromised over the years (from the original design), we now have a half automated\half manual means of switching over from heating to cooling. We are in Oregon's Willamette Valley, so during the spring and fall it becomes difficult to "guess" the HDD\CDD's for the day. Takes 2.5 to 3 hours to switch so we don't blow up the chillers (200 degrees down to 95).

Could I bury a 500-750 gallon reservoir tank or several banks\coils of tubing, and use it's treated water to speed up the heat to cool cycle. Ground temps are steady at 54 degrees. Has someone heard of or tried this? What issues would need to be resolved? Don't believe that this would be considered a pressure vessel since the system can be direct vented (automatically?). The boilers could cool naturally in their own closed loop. Any thoughts?

 

[317069]

What is the procedure that you follow to switch from heating to cooling mode and take about 3 hours?
Does tha hot/cold water serve air handlers and duct system or radiators?
could you describe your system little more?
two water boilers of total about 7200MBH plus steam boiler serve one pipe system(steam and hot water)

 

[DrRTU]

How about conversion to a true 4 pipe system and new chillers?

 

[walkes]

I would look at either a 4-pipe system or a distributed heat pump system.

Your buried system is a geothermal heat sink system (in your case a thermal storage system). Various configurations have been used for peak shaving, or in some cases to reduce the size of a geothermal field. (Ice storage, or thermal masses)

 

[SolutionsWanted]

Thanks for responding...
There are many factors that contribute to manual switching from heating to cooling. The system as been whacked on to the point that very little is auto-controlled. The buildings shell is very bad, we have valves that are uncontrolled and sensors that are faulty. I realize all of these things need to be addressed and they will be... but it will take time & $. We have air handlers, radiators. One 3600MBH boiler is for backup (although it is severely scaled and inoperable now). The steam boiler is only used for lab sterilization these days. We have laboratories in the center of the building with offices on the perimeters (both floors). Air is moved through the offices into the hallways then the labs and out the roof for safety reasons.

I realize this is all bad news, but we have to deal with it... which is why I'm looking for simple interim solutions. We have 3 zones but it would be difficult and expensive to add more lines. The boiler room is a large enough area to add a holding loop. Quick switching would make a major difference now as would valve\sensor\control repairs. Then I can focus on new efficient equipment.

 

[Drazen]

You still did not explain why swithcover takes those hours.

Do all radiators need to be cut off? If that is the case, additional on-off valves with thermoelectric or magnetic drives, triggered by central switch, installed on all radiator lines could speed up things.

Morevor, two-pipe system where you switch modes in middle of day makes no sense. If you are bound to daily switching for whatever reason, that should take place some hours before first shift, in early morning.

If you have breezing cold mornings, but sunny days, you need to cut-off heating early enough.

Once I had something similar, and users are coming in 8 a.m. with very cold feeling, and they themselves did not want to shut down heating before say 11 a.m, but heat accumulation made the place hell on earth until 5 p.m.

Forced shutdown of heating at about 9-9,30 a.m, solved the problem provisionally, but one janitor was in charge to estimate every day when to cut off heating, taking care that it should not be after about 9,30.

Such solutions are almost primitive, but work when options are limited.

You simply cannot cool water mass in circulation system immediately after shutting heating down, chiller will not work until temperature naturally falls to certain level.

 

[SolutionsWanted]

Thanks for responding, Drazen... the reason it takes so long is that our maintenance staff starts at 6am guessing the weather during spring & fall. As I stated, we have only one shared main line for heating\cooling. Whenever it's decided (in advance) to begin cooling and we've been heating because of cold mornings, it takes 2 to 3 hours to circulate the water until it's cool enough to introduce it to the chillers.

The situation you've had is quite similar to ours. But I'd guess the shell of your building was much better than ours. The exterior is 80% glass, and we intend to install insulated glass real soon now, but a small portion at a time as to not disrupt the office personnel during the work week.

Meanwhile, what I'd like to do is add a loop for taking the boilers off line (letting them cool naturally) and immediately introduce earth chilled treated water into the main line so that the chillers can begin pronto. I'm thinking coils of tubing (continuous 300' roll slide sideways) in a 5' deep by 3' wide trench would do it. What do you think?

 

[DrRTU]

Your statement was to make the building more efficient but you are focused on an auto change over w/o chiller damage. I don’t see how running the chiller will make the system more efficient. You will solve cooling complains but utilities will increase by running the chiller

Did you evaluate a simple air cooled fluid cooler?

http://www.mcquay.com/mcquaybiz/literature/lit_ch_cu/Catalogs/Cat_AFSD-1.pdf

Units can be installed above the boiler room in parallel with the boiler. An AHU with hot water coil ducted to the outside will work if the system is not PG or EG solution.

 

[SolutionsWanted]

Thanks DrRTU... yes I have and it is a viable option. I think we could cool with air if I could get the stinking radiators to cool sufficiently.

 

[317069]

usually in winter time when your maintenance staff started at six oclock morning, how loge it take the building to be warm and ready for employees.?

 

[SolutionsWanted]

Hi 317069... depends on temp, but if its say 34 degrees, it will take about 15-20 mins with only 1 boiler since we only go from 55 to 65 degrees. Heating is not an issue... just cooling after heating. We did discover today that we have additional piping that was put in with the steam boiler we use for just sterilization. That loop has 2 coils inside the air handler and the pipe has never been used... I'm guessing it was put in with the original building HVAC design "just in case" it was needed. The good news is that we can utilize the loop for more hydronic boiler capacity, which is badly needed, and heat\cool air!

 

[317069]

based on your information I guess that you have at least a 5000 sqft of radiators
Drazen has a very good idea about scheduling system operation.
the solution you are thinking about is a good idea too, but there is some points
- the geothermal exchange is usually used for heat pumps and the water temperatur is much way less than 180 or 200F.
- flow rate is smaller than your flow rate.
- if you want to use this option, how much time do you think will save and how much it will totaly cost, is the owner ready to pay this ammount?
- back to radiators, the radiator heating emission drop if the water temperature drop, if we use the same principal for the coils that you want to install, then when the water temperatrue drop the coil emission will drop too causing extra time.
- you had an idea about barried tank, what if you just connect a water tank that have enough voleum(same idea of open expansion tank) to your system and make pump and piping arrangment that when the heating is shutting off the pumps will suck water from this tank, discharged it into the system and pushing hot water to this tank

 

[SolutionsWanted]

Hi 317069... I'd guess 2250 sf of radiators. I'm told by our maintenance chief that if the controls\sensors\valves etc. we're in place and working properly as in automation, we wouldn't have issues. I think he's right except for: we lack water volume to make the system perform optimally; we have no option to quickly cool.

This morning is a perfect example. We started heating at 6am because the building was 55 degrees. By 9am, our offices on the west side were 80 degrees and the offices on the east side were 65 degrees. So, cooling started at 9:30 and my office on the west side cooled to 70 degrees by the time I left for home at 4:30. Once again we waited 2 hours for the 190 degree water to cool to 95 degrees before chiller was brought online! Like I said, if I had just 100 gallons of 54 degree water, I would have taken the boilers out of the loop at 9:00 and probably been able to bring the chillers on line by 9:30 instead of 11:30. Oh well!

So now we are trying to find HVAC technicians to fix it... been down this road before which is why the system is so screwed up. I'm guessing that we'll wind up throwing more equipment online and still have the same issues... but they'll be new ones!

 

[willard3]

Any and all system/control change will cost money and, what I get out of this is that the building owner won't spend any money to fix his problems.

The tooth fairy won't fix the system, money and engineering design will.

 

[317069]

- heating take 20 minuts, but how long it take to cool the building from 80F to 70F?
- how much water you have in your system?
- does your system use radiators on perimeter to stand the building shell losses and air ducts for ventilation.
- at 9 am the west side is 80F and east side is 65F ?
- you example shows that you are able to start cooling at 9 am which is the suitable time for employees and business

 

[tys90]

I'm not sure how applicable it would be in this situation but one project where we retrofitted a 2-pipe system we went to condensing boilers with hot-water reset. This allowed us to run 110F (instead of 180 or 200F) water during mild weather for morning heat and when it started to warm up the changeover was much quicker.

They used to run 180F water with the old boilers and had the same issues with having to wait long periods of time to changeover. However they also completely redid all the controls in the 2-pipe system which allowed them to changeover even faster using a couple different control schemes.

However, this was for hydronic fan coils not steam radiators but I'm confused, you run chilled water through steam radiators?

 

[SolutionsWanted]

Hi... after we've reached 80 degrees + on the west side, we cool until everybody goes home... west side never makes less than 75. I'd guess we have about 350-400 gallons online. Radiators are on the perimeter and they are not steam but just hot water. Yes we chill through the radiators and air. Thanks to all that have tried to help.

 

[Waramanga]

cooling through the radiators? how do you go with condensation? I like the idea, especially for places where you dont need tight conditions, just a bit of tempering for the stinking hot days, say for a school