Estimating System Volume

Zman

I have a client that has a large commercial hydronic system and we are trying to estimate the volume of the system for an upcoming glycol replacement. I do not have complete plans for the building so a piping takeoff would be challenging. I have heard of folks injecting a tracer chemical or marker into the system and then sending a sample of the boiler water to a lab after the chemical has been thoroughly mixed through the piping.

Does anyone have any experience with this process or does anyone have other suggestions? My WAG is that the system is >3,000 gallons.

Tinman

If you’re doing a complete replacement, could you put a water meter on the drain?

STEVEusaPA

Steve Minnich said:

If you’re doing a complete replacement, could you put a water meter on the drain?

I thought of that. But at >3000 gallons, he's going to have to dump (and somehow meter 1200 gallons to replace with glycol at @40%, or dump the entire amount.

Or using a cart mix in the glycol percentage. Maybe 1000 gallons at a time for the first 2, then 500, then 250, etc.

GGross

I am curious to find out how you solve this one, make sure you leave your notes for the next guy on that job!

Jamie Hall

The tracer dilution method does work, @Zman , but it isn't any too accurate unless you use fairly large concentrations of tracer. It's actually a rather straightforward dilution measurement -- one injects X gallons of a tracer of known concentration Y, and then measure the concentration after mixing, say Z. Simple in principal. X times Y must equal Q, the unknown volume, times Z. Piece of cake.

But... First, the tracer must be chosen to be completely non reactive and stable, and not be adsorbed by any crud or what have you in the system. Not too many of those compounds around. Second, one must be able to measure the various quantities to pretty high accuracy -- which in the case of Z, the final concentration, may not be all that simple. Or cheap. (The usual rule applies here. Since everything is multiplied or divided, the final result will be only as precise, in terms of plus or minus N percent) as the least precise measurement).

All that said, I have used fluorescein dye to estimate flow volumes in storm sewers that way, with a fair measure of success -- but I was only looking for plus or minus 10 percent or so.

hot_rod

Rhomar had a method for doing this, I don't see it on their site anymore?

HomerJSmith

Zman, how about this, I'm not sure it will work, just a thought.

Have a sonic flow meter on the return of the boiler. Start with a hot boiler and a cold piping sys and measure the temperature change at the sonic flow meter and run the boiler and when the temperature change starts going up, read the flow in gallons.

A pipe dream???

Of course, if it is a complete replacement with de-ionized water with a sys cleaning purge, drain it into 5 gal buckets and count the buckets. And...most important, be sure and have a lot of people there so you have enough fingers to count the buckets. lol

EBEBRATT-Ed

Yes putting the trace in works. Call a water treatment guy. We did this several times and it worked out ok.

Zman

Thanks for all the suggestions.
The water quality is pretty good and a system drain down would be a major PITA (refilling and purging 100+ units would be the hard part). I did a piping takeoff on just the boiler room and came up with 1,150 gallons. I am thinking the system may be bigger than I originally thought.
It seems that a tracer is the only viable option.

EBEBRATT-Ed

@Zman tracer is the only practical option in a building that size. Don't know your location but I am sure you can find a water treatment guy to assist with the tracer.

We used to buy the glycol straight unmixed. For a big job if we had an idea of the volume, we would pump in 2 bbls of water and one of glycol (33%) until the system was full

EdTheHeaterMan

@Steve Minnich I'm guessing that @Zman wants to remove the water in the system without letting any air in to avoid the need for purging the multitude of emitters in the building. Of course removing boiler water without allowing air into the system sounds impossible but if you know the quantity beforehand, you can replace the drained water with strait antifreeze (AF) if you can inject the antifreeze in the supply and drain the water only from the return. This is why knowing the volume before you start the draining process, you don't need drain the entire system dry (or as dry as you can get) and measure the amount of water leaving. I have done this at a school building by isolating the boiler from the rest of the system. Then add AF until the return started to show some color. I was about 90% done when the color started to change. I added the rest of the antifreeze to the boiler in the same fashion. Forced the AF in the return and released water only until the color changed. I got all the AF into the system before the boiler water changed color. After 2 days of circulation the test showed the system was about 45% Glycol. I was shooting for 50% but guaranteed 30% in my contract. This was a success but I had an idea that the entire system was about 300 gallons so I ordered three 55 gal barrels. Not one bit of air was let into the system and no air purging was necessary. So, I understand the need for knowing the system volume before you start the project.

Measuring with a meter would involve an empty system at some point, and the need for purging. Although the idea is a good one for commissioning a new boiler, in this case it is not practical. You got to use your head in the big stuff!

Zman

So I spoke with a local water treatment friend of mine, and he said they usually use salt which of course is a bad idea for a hydronic system.

I then decided to contact Rhomar as @hot_rod suggested. It took a bit of nudging, but once they got a chemist on the phone I got some answers. Rhomar does offer the service. They normally want the system flushed first, but since they recently tested the water in this system they were comfortable adding tracer to the water in the system (apparently iron can be a problem). The process goes like this: take a sample of the system water first and save it, add 5 gallons of tracer solution and let it circulate for a few days, take another sample of the boiler water, and send both samples back to Rhomar so they can estimate the system volume. It should cost a few hundred bucks for the tracer, testing and shipping.

In an effort to reduce the labor cost of opening all the zone valves and purging hundreds of locations, I am thinking that it will work best to pump fairly high concentration of glycol (65% or so) in the boiler room and primary piping and then let the system blend it together. I know a guy (maybe me ) that once tried to put 100% glycol in the boiler room piping and then turn on the pumps. If you like pink whipped cream give it a try.

hot_rod

The strong solution method does end up wasting some glycol if the % was not high enough. In a large system like that it could get expensive.  Why not inject 100% at some distant location, use a gear type pump like we used for glycerin injection in fire protection systems.