twin mod/cons w/indirect on 24 unit apt

Patrick Linhardt, \"Linhardt's Field Guide to Ste

Hi Ken,

Sorry to confuse you. Yes, on paper the better system used more gas. Nailing down the variables will be next to impossible.

I was trying to simplify by leaving out the fact that one of the buildings uses W/M Ultras, installed the previous year. That building had the highest bill. In its defense, we found that the tekmar #261 had been tweaked by the maintenance man to a higher reset temp, we put that back in line with the others.

My real question was the set-up for the twin mod/cons and if anyone else had experience using those with the indirects.


Best regards, Pat

Patrick Linhardt, \"Linhardt's Field Guide to Ste

twin mod/cons w/indirect on 24 unit apt bldg

I'm posting to get some feedback on control and parameter settings for a job where there are five 24 unit apartment buildings with twin gas-fired modulating/condensing hot water boilers. Two buildings have indirect fired hot water, three are just heating. All five use tekmar #261 staging controls. The buildings in question have two Solo 250 boilers with one TL-100 indirect. They were installed in the early fall of '06, and have run without a hitch since.

However, the property owner wants to maximize efficiency and so do I. The contractor and I went to the jobsite this afternoon to look over the last energy bills. He had called last week to report the low bill of the five essentially identical buildings was $600. That's $25 per unit for the coldest month we've had around here in a while. But the kicker was it wasn't a building with the new indirects. They came in at an average of $740 or so. Not at all bad at $31 per unit, but why higher than the buildings with the standard water heaters?

The maintenance supervisor had some interesting suggestions, like "the low lifes without jobs live in that building" or "they don't take showers over there" or "some people leave the hot water running all day for their cat". The contractor and I wanted to check out the equipment. We had set them up to bring both boilers up to 186F on a call for domestic hot water, priority courtesy of the Solo's control module and wiring. Both boilers have their own DHW circulator w/IFC, so we could stage fire the boilers if needed.

Today we decided to do a little experimenting. We are now running one building on just one boiler for DHW, using 186F, 30 second pump post purge. The other building is running both boilers for DHW, using 156F, 5 minute pump post purge. The tekmar controls have identical settings and are only used to stage the boilers for space heating.

Any predictions for which setup is going to be more efficient? Any suggestions on alternate strategies? Any experience with this equipment operating this way? Thanks in advance for your responses.

I have attached the reset curve the boilers use for space heating.

Best regards, Pat

Ken_40

That's confusing...

as hell!

I'd try and do a few drive bys, looking for windows cracked, gas ranges on (a low-rent "solution" to only allowing 70F on the stat(s)) and perhaps verify a lot of sassumptions, before tweaking controls and the like. Especially, since the evoidence is sugesting the better system is getting the worse economy of operation!

Or did I read that wrong?

Mitch_4

comparing the gas bill

is part of the equation.. What was the water consumption in each? that is the other part I see you needing.

If the ones without the indirect used 100 galons, and the ones with indirects used 1000 gallons...you get the idea.

Ken_40

Good

point!

Mitch_4

yeah but I

am assuming a similar heatloss...and you know what assuming is...

Patrick Linhardt, \"Linhardt's Field Guide to Ste

water bills

Hi Mitch,

Good point. I will try to get the water bills to check consumption.

Best regards, Pat

[Deleted User]

Tenant Occupant Loads

THey could have people stacked like cord wood come sleepy time. Been there, seen that, got the T shirt to prove it:-)

3 bedroom apartments with 15 people living in them...

Now THAT Will throw your numbers off, and they're typically not there during the day. THey have jobs, dontcha know.

Speaking from experience, on older (circa pre 1940) systems, we do an ODR based on a minimum of 150 degrees F, 185 degrees F max, and our systems are typically cascaded.

On post 1940 systems we use a 140 minimum and a 180 maximum. We also stage pumps based on the OSA temps.

For DHW, we use the Turbomax reverse indirect and rarely set it for more than 10 degrees F over our target tank temperatures.

ME

Patrick Linhardt, \"Linhardt's Field Guide to Ste

Hi Brad,

Also a good point. Tenant levels and lifestyles have an effect on usage also.

These buildings are in a middle class neighborhood with low density occupancy. The floor plans are very similar. Buildings have decent replacement windows and were built in the late 60's or so.

Best regards, Pat

[Deleted User]

You obviously have me confused with someone who knows...

what they's talking about, Ted...;-)

ME (or BWC, or HR)

Weezbo

When the water heaters run out of available hot water...

the people turn off the tap,shower whatever and get on with life..when the boilers can basically produce limitless hot water....the wake up call to get out of the shower ,..stop running hot water on the one plate spoon fork and cup in the sink and apply elbow grease soap and a dish cloth...just doesn't alert the residents to what they are basically wizzing down the drain. *~/:)

This question is somewhat like AFUE and the larger picture of OverAll Energy effectiveness.

Ross_7

Mod/Con twinning

Patrick,
You need to use the AM4 modulation signal interface. You should be using a 265 of dual modulating outputs, or tekmar 270 can be used with two boilers if wired correctly. The Ultra uses the same controls as the Triangle Tube boilers. There is a schematic on the the Tekmar website, on how to do this correctly. Then the boilers will "jive the way they should. Good Luck!
Ross

Rocky_3

Like Weebo said...

check the water consumption between the indirect and direct fired units. if the indirects can essentially make hot water on demand, the tenants never run out of hot water, so therefor have no impetus to remove themselves from the shower. therefor, 10 minute showers now become 30 minute showers. therefor, the more efficient system now costs more because the hot water usage has now quadrupled. No good deed goes unpunished.
Rocky

Patrick Linhardt, \"Linhardt's Field Guide to Ste

on the domestic side

Hi Ross,

Yes, that set-up will maximize the space heating,but my question is on the domestic side. How to get the most out of the adjustment to the parameters available?

Best regards, Pat

Patrick Linhardt, \"Linhardt's Field Guide to Ste

like herding cats

Hi Rocky,

I think its turning into an attempt to herd cats. Further adjustments can be confused with unknown variable changes. Huh?

Best regards, Pat