What's the right amount of Delta T?

Steve Rockwell_2

I have a new Ultra 155, pumped primary secondary with the included Taco pump, with two zones on constant circulation using Grundfos 15-58 pumps. My house is a combination of copper fin baseboard with four ci rads.

This morning, it is running at 132*, with return temps about 120*. Regardless of the temperature setting the boiler calculates, the delta T is never more than about 10-14*. I often read about a 20* delta T here, and I'm wondering if I should slow down the pumps to get a greater delta T and perhaps more efficiency through the system. The pumps are currently set on "3" which I believe is full speed. Am I getting all I can get out of this boiler with this small delta T, or should I slow the grundfos pump speeds down?

By the way, just got my first full month gas bill yesterday, and my therm usage is down 46% vs. last year with the old American Standard boiler. I don't know what the weather comparison is, though if I had to guess this month certainly isn't warmer than normal. Any sources for degree day info so I can compare? It's not listed on my gas bill.

Thanks all.

Mark Eatherton1

Nothing like a nice warm mug of delta tea to study utlity bills.

Delta T is subjective. It depends on which delta T your'e talking about. The delta T on the "source", AKA the boiler primary in your case is a variable/fixed delta T. The flow rate is fixed, the fire rate is a variable. Hence, variable/fixed:-)

The delta T across your "load" is also a variable. If you have non electric thermostatic controls on the load, the system delta T is a funcion of load. No load, low delta T. Big load, big delta T. Of course, this also depends on how you have your flow controls set up. If you have low flow, you could see a big delta T, which doesn't necessairly mean a big load. If you have a pressure activated bypass (PAB) at the far end of the system, you may see little delta t's during minimal loads, and big deltas during major loads.

If your PAB is located right at the main system circulator, the opposite may be true. Small load, BIG system delta t because flow "out to" the system is low.

So, as with any hydronic heaitng question, the correct answer is, "IT depends".

You want some suger for that mug of Delta Tea?

While you're siping that tea, think about this. Which moves more energy. 100 GPM at a 1 degree rise. or 1 GPM at a 100 degree rise... Do the math. Gallons time pounds times delta T = BTUs.

Pass the Sachryn please...

As for degree days, try ftp://ftpprd.ncep.noaa.gov/pub/cpc/htdocs/products/analysis_monitoring/cdus/degree_days/archives/Heating degree Days/Monthly City/1997/august 1997.txt

or http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/cdus/degree_days/

or just Google Degree Day Data. It's out there, you just gotta dig for it a little...

ME

Steve Rockwell_2

Huh?

Slow down, big boy. Just a dumb homeowner here!

I was talking about the supply and return temps as reported on the Ultra's readout. When I complete sipping my tea, will I have realized that the two both put out an equal amount of BTU's and therefore don't worry about it?

Just wanting to squeeze every $ out of my investment. And trying to bankrupt (okay, reduce the profits of) the gas company at the same time.

I understand what you mean about the primary being fixed in regard to gpm, but variable in terms of the boiler's output. But does it make sense for me to slow the zone pumps down from 3 to 2 or 1 to get a higher delta T?

Thanks for your help Mark.

Bill Nye_2

Steve

Go ahead, flip the switch. What could it hurt? Slow it down for a day or two, if you don't like it put it back. The boiler police won't arrest you.

The nice thing about having the stuff in your own home is that you can "experiment" w/o getting an angry phone call [unless of course you manage to make your spouse unhappy]

Uni R

3 Speed and DeltaT

I'm thinking that if it made a difference it would actually be best at the highest speed (other than the fact you are using more KWHs in the process).


The faster water goes through a heating circuit the more heat that circuit is giving off. While this would lower the Delta T on the heating circuit itself it should in fact help the boiler loop raise its Delta T. Or maybe I am suffering from excessive paint fumes...


I would still try lowering the speed just to see what happens. At best, the delta T on the boiler loop will be lowered an insignificant amount and you'll pocket $5 per year at medium speed or $15 at low speed. *Assuming $0.11/KWH x 24 hrs x 200 days

Mark Eatherton1

Lazy water...

If you slow it down too far, the water, being lazy, will follow the path of least resistance. You may find inadequate flow on the far ends of your system. Now in the event your system is piped parallel reverse return (doubtful) you'd see a bigger delta T with slower flow...

Didn't really mean to cornfuse you. Delta T is really made up of nothing more than the addition of or deletion of btu's. The more you add or take out, the bigger the difference.

Like the Non Science guy said, go ahead, experiment around and see what happens. Remember this. All of these components were sized for worst case scenario. If you are at any condition other than worst case, it is OVERKILL, so turning your pump speed down will be fine for now, but you may need to boost it when it gets colder.

Let us know how you make out with your experiment...

ME

jerry scharf_2

pump speed and efficiency

Steve,

Your instincts are right, but you'll need to watch it carefully and may need to reprogram the outdoor reset curve.

If you slow down the flow on the loads, the return temperature drops. The lower return temp will improve the condensing level of the boiler. I'm not sure I quite believe this, but the rule of thumb is every 3 degrees F of reduced return temp will produce 1% increase in efficiency. If all else is the same, I like to see the return water as cold as practical.

But there's more to the system than that. As you increase the delta T while keeping the supply temperature the same, you have lowered the mean (average) temperature of the emitters. Baseboards are especially non-linear in response, so you may find that there's now not quite enough output to heat the rooms. Thus the comment about the reset curve may need to be changed.

Like Bill Nye said, flip the switch on the pumps and see what happens. There is nothing I can see that could harm the system by doing so. I would also do them 1, then the other, then both. Live with each setting for at least a week.

For historic weather information, ME turned us on to www.wunderground.com. It should have all the information you need. This year may be normal, but last year was cold! You may have to live with 35-40% instead.

jerry

jerry scharf_2

oops

double post

Reynz_2

Delta T

Steve,

A Weil McLain engineer told me about my Ultra 155, that an Ultra likes 10* at the boiler loop and 20* on the system loop for a Delta T.

The Delta T on my boiler loop (the one with the tempature readout) goes anywhere from 5* to 14*, depending on if it is warming up or maintaining the tempature in the home. Just to let you know, at constant circulation (VERY IMPORTANT), with the boost feature turned off, and a conservative set heating curve, I'm maintaining 71* in the house at about 128* water tempature on a 30* day. My Ultra is almost running 24 hours a day.

I've been all over this Ultra 155, so if you have any other questions, let me know. I have a B & G 100 on my system loop because I have a converted gravity system. I also have Weil McLain low profile CI baseboards.

I have about 1 to 2* difference between my upstairs and downstairs tempatures.

Chris_43

Delta T

Reynz,

If you get a chance could you list some of the settings on your 155. When I mean settings i'm talking about paramaters 1-10 and 22-27. I have an 80 installed in my own house and I'm trying to fine tune it. Also, does anybody know where I can get the GASCOM software. My local distributor does not have it.

Thank,
Chris

Weezbo

howdy.

whether in the minds of mortal man it is better to have narrowed the delta "T: or to have not.....
Weezbo.

Reynz_2

Settings

Ok,

Para
4- 158,
5- 100,
6- 0,
7- 65,
9- (-4) Needed to adjust the temp guage,
10- 100,
11- 0,
13- 27 (Max fanspeed lowered for oversized boiler)

I didn't change 22-27. Don't know enough about it yet, and I don't seem to need to..... If you have an opinion, I'd like to hear it...

Why do you need the software?

Chris_43

settings

I have pretty much the same.

Para 4 - 160 , 5 - 90 , 6 - 0 , 7 - 66, 9 - 0 , 10 - 84 , 11 - 0 , 12 - 0 . As for 22 and 23 I have not played with them yet, but these will control the temperature overshoot from the calculated setpoint. Do you have para 3 set to 1,2, or 3?

The software will let me monitor the system all day from my computer and allow me to setup new ultras faster.

Chris

Reynz_2

Settings

Oh, changed Para 4 to 166.

As far as Para 3 is concerned. I have it set for 1, which is boiler loop circulator to come on with a call for heat. 3 is constant circulation for loop and I beleive 2 is also. I don't think this should ever be changed. It should only be set to constant circulation if the boiler circulator is the only one used for the entire system, which is not supposed to occur. There should be a minimum of two circulators, and a third if one uses DHW.

Mark Eatherton1

On narrow mindedness and narrow delta T's...

Some engineering types are narrow minded, and like to use narrow delta T's in their design specifications.

This results in GROSSLY oversized circulators being applied, which results in excessive energy consumption, higher maintenance costs, and onging complaints about hydraulic noises, vibrations and the such.

How do I know this? Because WE get the call from the recently completed installations where we initially told them that the system was OVER engineered, and UNDER designed. To boot, we told them the problems they were going to have. Makes ya want to sit back and go NA NA NA NA NA nah... But we're professional, and we don't do that kind of thing, in front of the customer...

The American engineering culture, for the most part, is STUCK on this narrow differential thing, and they're basically trying to cover their butts. They don't want to get the call about cold rooms, so they oversize EVERY component in the system so that THEY don't get the call... And they DON'T get THAT call. But they DO get the vibration/noisy/overheating calls that WE get to go out and trouble shoot and correct by substantially DOWN sizing the equipment.

When will they ever learn.

I have seen a 20 degree delta T on ONE, count 'em ONE hot water baseboard heating system, and that was when it was being started in the dead of winter with EVERYTHING being cold.

What it boils down to is this. Even on systems that I know for a FACT were properly designed by myself using "normal design practices", when I show up on a design day and see the system running at 50% of its capacity, that tells me that ALL of the components are TWICE as big as necessary based on real time energy loads. And it's backed up by seeing delta T's that are half of what was designed for. At "design conditions"...

It tells me we need to back off of the theoretical and look to the practical for design guidance. We're designing for worst of WORST case scenarios, and it's really not happening in the "real time" environment.

Time to take a deep breath, step back and look at existing situations, and go forward from their with "real time" experience IMHO.

Thanks for listening..

ME

Gordy

Micro DT's

Mark in a radiant system there are several delta t's. In a mix down type application there is the following delta t's.
Main return and the boiler supply.
Main return and mixed down supply to the radiant loops.
The loop supply and return.
The fluid and pipe wall in the loop.
The pipe wall and the medium the pipe is imbedded in.
The medium and the room Temp.

Which of the these delta T's do you find most important? I know it sounds a little crazy breaking down some of these "micro" delta t's. Just wondering if anyone considers these and which they pay the most attention to.

Gordy