Increase in system run time question to ponder

Dave Yates (GrandPAH)

How much added run time does a mod-con using ODR add??? Would you figure 20%? 30%? 50%? 90%?

Trying to wrap my brain around cost projection figures for estimates where I'm selling an upgrade from an older chimney-vented boiler to a mod-con using a full-range ODR curve (we're seeing lots of standing CI rad jobs where ODR is a perfect comfort-partner).

Mark Eatherton

I'm thinking...

80 to 90 percent. I remember when I first installed the little Munchkin in my house, and it ran, and ran, and ran. I remember thinking to myself that I was going to have to empty out my savings account to my wife who usually pays the gas bills. When the bill finally came, it was lower than it had EVER been.



BTW, congratulations on 10 solid years of writing for Contractor Magazine mate! (belated because the actual anniversary was last month)



ME

Dave Yates (GrandPAH)

congrats!

And for 10-years of hydronic advice. Time do fly! Hard to believe it's been such a seemingly short ride.

I too had 90% in mind because of setting the curve over a full glide and by having the boiler sized properly for design conditions. On a P/S app with multiple zones, the P-circ must be at, or near, 100%.

Tim McElwain

I was just

at a Viessmann training seminar and they were quoting figures of at least 75% or higher, of course with their product and ODR they were estimating 90% or more.

NRT_Rob

man, that's an interesting question

if you assume a min mod of 25kBTUs and a boiler non-mod output of 75kBTUs, you'll get 3x the runtime for all loads that result in the mod/con cycling. for all loads above the min mod on the modulating boiler, you improve the non-mod 1/3rd run time to 100% run time (assuming perfectly sized boiler, from 25kBTU load to max load) all the way to 100% the whole time.



without bin data it might be hard to calculate that, but it stands to reason it's a huge increase in run time.



the *real* question is what does that mean? for instance, if you had enough thermal mass to just run all of your hours continuously, and then pull heat off of the mass for the rest of the winter, run time wouldn't help you in any case... you would get a single steady demand in both cases, it would just last a different length of time. So run time would not be a helpful metric for that hypothetical system... I think.



what you're really interested in, I think, is cycle count, given that each cycle is much less efficient for the first few minutes? and that gets the system mass into the equation, with standing CI radiators especially.... and I have no idea where to go from there right now.

Mark Eatherton

Credit given where credit due...

If it weren't for The Wall and Dan Holohan, we'd just be a couple of regular Wallies.



But as it is, we are regular Wallies with 120 articles each behind us, AND the prestigious Carlson-Holohan Industry Award of Excellence to boot.



Thanks for all you've done and will continue to do for our industry Dan .



ME

Dave Yates (GrandPAH)

the meaning of life......

It means, from my personal perspective, that our hi-eff boilers should last longer due to longer gentler (if that's a word) extended cycles - fewer off/on cycles. It also means our customers could see a spike in electric bills depending on how we design the systems.



Home Power Mag noted hydronic systems can be the best mate for off-grid PV solar, but stressed the system design can adversely impact the PV load and cause a large increase in the PV system's cost. Granted, that's not something I expect I'll be dealing with (off-grid systems), but we are bidding numerous grid-tie PV systems and part of the design-process requires in-dept analysis of the loads and, more importantly, what can be done to reduce those loads. $1.00 invested in load reduction can yield a $4.00 reduction in the cost for the PV system. So..... Even though not off-grid, the hydronic-system design still has the potential to have a significant impact on the PV system's design.

Mark Eatherton

Sounds like a solid case for ECM pumps....

Primary AND secondary. This way, the circ's only sip the energy necessary to satisfy the load.



Everything in modulation! My new mantra :-)



ME

Gordan

But which mod-cons can "deal" with a modulating circ without getting confused?

I know that the previous generation Vitodens 200 had a bus pump and modulated both the pump and the burner, but they took it out in the new one. (And according to what I've read here, the built-in converter negated at least some of the energy-saving benefits of variable pumping.)

CC.Rob

load analysis

I'm completely on board with the cycle count thing, and the use of as few ECM circulators as it takes to move the water. But... the electrical draw of the modcons appears to vary quite widely. So much so that I wonder whether the GAMA certs are an accurate reflection or are reported consistently. For example, according to GAMA, a Knight KBN 105 has an Eae of 1386 kWh/yr, while a TT Solo 110 is 378 kWh/yr.



A factor of 3.7 difference is definitely something to consider, along with whether you need one pump, two, or whatever.



And let's also throw into the mix a load-based control system, rather than plain vanilla ODR. That should help, too, at little additional cost in a simple implementation.



And a zoning strategy that requires little or no power to operate, e.g., in a simple form for retrofits, zone valves that only draw power when in the act of opening or closing.



Fascinating subject.

Dave Yates (GrandPAH)

scratching the surface

Agreed! Seems to me we've just begun to (barely) scratch the surface and, let's not forget, we're headed to a point where we will be comparing watts-to-watts with the air-side of the industry. The fact is, hydronics can kick arse if, and only if, we mind our P's and Q's and W's. ECM blowers are rapidly becoming standard-fare in the air-side and that too, as they say, changes everything.



Don't know bout you all, but the stats req'd for 2-stage and ECM blowers are altering the playing field and not everyone on the customer side is enamoured with the newer stats. Personally, I like the robust capabilities from the programming and communicating side, but our customers want simpler things as they age.



Cripes - tonight's news had an electrician chasing 3-watt ghost loads with a kill-a-watt meter. Consumers are dialing in on this side of what it is we do and I'm paying attention.



React - change - react - change - it's a never-ending cycle. The faint-of-heart need not apply(G).