Fuel Smart Hydrostat 3200 plus and damper issues

[patrickoneal]

I have a Dunkirk PWB-5D boiler, a 40 gallon indirect tank, and two zones of fin tube baseboard radiators. All was working until today after I installed a Hydrostat 3200 aquastat and a Taco 3 zone controller.

I changed the aquastat to try to save some gas, and added the zone panel to clean up the wiring and to use the zone 3 dry contacts to signal the Hydrostat on the I1 and I2 terminals to bypass the energy saving features when hot water is called for.

I got everything wired up neatly, and I assume correctly. I powered the boiler back up with all my thermostats off, and adjusted the aquastat on the indirect tank until it called for heat(it's right beside the boiler). The zone panel indicated the call, the zone valve opened, the zone panel indicated the end switch closed. The hydrostat then opened the damper, but it didn't stop in the open position, and it started clicking like it was bouncing off a stop. I powered everything down and checked my wiring. I messed with the auto/hold open switch on my damper to get it to stop in the open position, but the boiler still wouldn't fire.

I then shut the indirect tank off and tried zone 2 of my baseboards. The zone panel again indicated correctly, zone valve opened, and the damper started moving. This time it decided to just keep spinning, 360 degrees over and over(is there a mechanical stop on those things?). I switched the hold-open switch to stop it in the open position, and the Hydrostat 3200 started making some strange noises. Then a small amount of smoke came out of it(the hydrostat).

Does anyone have the pinout for the 6 pin damper connector? Is it supposed to stop on it's own, or does the aquastat signal it to stop?

I'm going to reinstall the old aquastat(I can't trust the new one after it smoked). I'm 99% certain that the hydrosmart stat I got is defective.

Besides my questions on damper operation, can anyone recommend a "smart" aquastat? I'm not sure I want another Fuel Smart 3200.

 

[patrickoneal]

I reinstalled the old honeywell aquastat just now... I left the zone panel in place, landed the burner control, t-stat, power, circulator, and plugged in the damper. The only thing I couldn't hook up was the extra pair for economizer bypass on hot water calls(because it's a dumb stat). Everything is back to normal now. The damper stops where it's supposed to and the boiler fires.

I'm thinking either the Hydrostat 3200 was defective, or the pin out for the damper is wrong. It's strange that they don't document the pin out the aquastat expects. I'm baffled.

 

[Sponsor]

 

[Dana]

The Intellicon HW+ (formerly called 325o HW+) is a fairly keep-it-simple-stupid heat purging economizer that's fairly DIY friendly to install.

Effikal makes the dampers for the more recent versions, but it has a 4-pin not a 6 pin connection. Have a picture of both the damper and the connection, or better yet, the model number of the damper?

 

[patrickoneal]

The damper is an Effikal, and it does have a 4 pin molex on the damper itself. The other end of the cable has a 6 pin molex with a jumper on it, and plugs into the aquastat(it plugged into the 3200, and is currently plugged into the old Honeywell aquastat since the new "smart" one decided to burn up. I assume the 6 pin connector is "standard" as it's what both aquastats accept.

As for energy saving, I got a refund on the 3200, and got a Taco SR501-OR-4 outdoor reset instead. I got it mounted and powered tonight, and I'll get the sensors hooked up and tie into the boiler as soon as the high-temp pipe insulation I ordered shows up(for the boiler temp sensor)

 

[Dana]

Outdoor reset isn't usually the ideal strategy for an oversized cast iron boiler (and unless your house is larger than 10,000 square feet, the Dunkirk PWB-5D is going to be oversized for the space heating load), since operating at lower system temperature tends to short-cycle the boiler, reducing rather than enhancing average combustion efficiency. The lower temperatures lower the standby & distribution losses, but that's usually eaten up substantially by the cycling losses. The only way the ODR control would save fuel is if you have high mass radiation, and a LOT of it. The PWB-5D's output is over 120,000 BTU/hr, and it's highly doubtful that any one of your zones has enough radiation to deliver 120,000 BTU/hr of heat even at 200F, let alone at the lower temps needed to track your average wintertime load at max comfort.

Heat purging economizers tend to work better, utilizing the available thermal mass in the system to maximum benefit, making far fewer but longer burns. Heat purging economizers utilize the residual heat in the boiler at the beginning of a call for heat, until the boiler hits it's low temp limit, then cycles it up to the maximum temperature. If/when the high limit is reached, it continues to purge the boiler down to the low limit. The economizer also anticipates the end of a call for heat based on recent system behavior on recent calls, and cuts the burner early, purging the boiler to a lower temp to finish satisfying the call, parking the boiler at a temp well below it's maximum, to minimize standby losses.

But outdoor reset maximizes comfort, and if that's your goal (rather than maximum efficiency), knowing your actual heat load makes tweaking it in to perfection a lot easier.

An average 2500' house in Virginia has a design heat load less than 30,000 BTU/hr. An antique uninsulated 2500' house with all single pane window and high air leakage might have heat load as high as 60,000. Almost no houses in Virginia have heat loads as high as 120,000 BTU/hr, but there are plenty of boilers that big (or bigger) installed in houses that don't have anywhere near enough radiation to emit the full boiler output. If you have a few of last winter's gas bills with exact meter reading dates and amounts and a ZIP code to find the nearest weatherstation for daily degree-day data, it's pretty easy to establish an upper bound on your true heat load .

With the load numbers and the amount of heat emitter (by zone, and the total), you can estimate the water temperatures at which the radiation is just barely keeping up with the load, which is where you want to be in order to deliver the steadiest, most even temperatures, with a minimum of undershoot or overshoot.

 

[patrickoneal]

Thank you for the detailed response.

My motivation to get an economizer or outdoor reset is really more about comfort than saving money, but saving money would be nice. My baseboard radiators are pretty noisy when they warm up to 180 degrees, lots of clicking sounds from the metal expanding. I'm hoping running at a lower temp will quiet them down a bit, and that they'll stay heated for longer instead of making a bunch of noise getting up to 180 then cooling off right away.

I agree that the boiler is way oversized, the house is a 1 1/2 story and it's a little under 2,300 sf. It was here when I moved in. I added an indirect tank, and it really is nice to never run out of hot water, but if this boiler ever dies, a smaller one is going in.

I like your method of figuring out the heat load. I'll see if I can access all of last winters gas bills online. I don't think replacing the boiler with a smaller one would pay for itself, but if I found a good deal on one I'd do it for better comfort and less cycling.

 

[Dana]

Replacing a functioning boiler with less than 15 years on it never pays off in fuel savings. But there are some pretty inexpensive stainless fire=-tube heat exchanger modulating condensing boilers out there now that are cheaper than cast iron, some that modulate down to less than 10,000 BTU/hr out. If you're ever inclined to go that way, be sure to run this napkin-math first, as well as the heat load calc.

When you have the load numbers see what you need for water temperature on design day. If it's all typical fin-tube baseboard, this chart should help. If it looks like you have enough heat emitter to get there with 140F or cooler water on design day, you may just want to slave the boiler to the indirect tank zone only, and tap into the indirect's zone plumbing to sip heat out of the hot water tank for the space heating, using an outdoor reset mixer valve to vary the output water temp. (That's a lot of sheer hackery to be sure, but it works in low to middlin' load houses.) That way all burns are working with the thermal mass of the indirect. It's essentially re-inventing the high mass boiler, but high mass is what you need with a 120K of burner output.

 

[patrickoneal]

I think the boiler is around 10 or 15 years old, I'd have to look at it to make sure. My thoughts were similar on payback, and I've heard that mod-cons don't last nearly as long as a cast iron boiler and require more frequent repair. I did the math when I replaced my split A/C for downstairs and it actually should pay for itself(went from 10 SEER to 16 SEER and downsized 1/2 ton). The old unit was 25 years old and leaked, I was tired of charging it and tired of the house being 70 degrees and humid from short cycling, so there was a comfort factor as well. Upstairs I installed two Daikin minisplits and got rid of the ductwork and air handler in the hot attic. Those likely won't pay for themselves, even with my "free" labor, but it's one hell of a lot more comfortable up there.

I've attached my gas usage history, in the summer it's quite cheap just running the indirect and gas cooktop, however the garage gets awfully warm. In the winter it's actually kinda nice to have the garage warm from the waste heat. I'll look up the degree day data to see just how oversized I am. I did something similar a while back to see how much electricity my new A/C systems were saving me, and it was substantial.

 

[patrickoneal]

Also, I meant to say thanks again Dana. This is quite a bit of interesting information to go through.

That gas usage history changed from CCF to Therms in February, not that they're too much different.

 

[Dana]

Mod cons with aluminum heat exchangers have longevity issues when the system water chemistry is ignored, and poorly implemented system designs can do-in just about any boiler. Fire tube stainless heat exchangers are inherently more forgiving, and have a pretty good track record, even though the modulating burners and associated controls add a bit more complexity and potential points of failure. Triangle Tube has well over a decade of pretty favorable history on their fire tube boiler models, and have improved somewhat in overall reliability over time. HTP is importing a and supporting a pretty good Korean stainless fire tube boiler series at very attractive pricing that should go the distance, but only time will tell. (I know of a couple of hydronic designers that were died in the wool Triangle Tube fans who have now been installing mostly HTP's UFT series, in no small part due to the much higher 10:1 turn down ratio, as well as the low price point.)

Having the boiler in a garage rather than inside of conditioned space means that the very substantial standby losses are nearly all truly lost. If the boiler were in a basement or a separate insulated boiler room in the garage, without an insulated wall between the boiler room and the house the standby heat would end up mostly in the house. With a right-sized modulating condensing boiler it can live in a closet-sized space, unlike the behemoth in the garage.

Looking at your billing from last year, over the January into February billing period the outdoor temp averaged 42.3F over 31 days, and you burned through 194 therms at about 81% combustion efficiency. That's 194/31= 6.26 therms/day input, x 0.81 is 5.1 therms/day entering the heating system. That's 510,000 BTU/day. Assuming a heating/cooling balance point of 60F the average HDD60 was 60F-42.3F= 17.7 HDD, so your house (including standby and distribution losses) uses 510,000/17.7= 28,814 BTU/HDD or (/24=) 1200 BTU/degree-hour.

A typical 99% outside design temperature for Virginia is about 15F in the interior, about 20F along the coast. At 15F you have (60F-15F=) 45F heating degrees, for an implied load of ( x 1200 BTU/F-hr=) 54,000 BTU/hr. That's 23-24 BTU/hr per square foot of conditioned space, which actually quite a bit on the high side for a 2300' house. Something like 15% (maybe more) of that is standby loss to the garage from the oversized boiler, so the heat loss of just the house is clearly going to be under 50,000 BTU/hr, but probably not less than 40K. A current code-min house that size with code-max leakage would come in under 30,000 BTU/hr @ +15F. That implies you may have some significant air leakage, low R-values in the walls &/or attic, a lot more window area than usual, or perhaps a bunch of single pane windows?

No matter what the reason for the somewhat higher heat load or higher standby loss, a boiler with 75-76K of output dropped in the same spot would still have you covered at sub-zero temps. A boiler with 120,000 BTU/hr of output (like the one you have) has you covered down to -40F, assuming you even have enough baseboard to emit the full 120K.

Since the boiler is more than 2x oversized for the load it's true as-used efficiency isn't as high as it's AFUE implies since it's running a lower duty cycle, and a greater fraction is given up to standby. AFUE testing assumes no more than 1.7x oversizing, and assumes the boiler is inside of conditioned space, neither of which is the case here.

 

[patrickoneal]

Thank you for all the information.

I am very close to the coast in Portsmouth, VA.

You nailed it on the air leakage and the single pane windows. I've replaced 6 of the windows with high quality double panes that will never pay for themselves. As for air leakage, it's a cape code style home and the lower attic(devil's triangle) needs work(knee wall access doors need proper sealing and insulation, the backs of the knee walls need sheathing). The upper attic needs more insulation as well. It's been on my to-do list for a long while to tighten everything up, I just hate crawling in the attic. You've certainly enlightened me on just how bad it is.

 

[patrickoneal]

Also, I keep the house at 68 in the winter. Is the "balance point" you spoke of the thermostat setting?

 

[Dana]

The heating/cooling balance point in most houses is 5-10F below the thermostat setting, since 24/7 plug loads like refrigerators & DVRs are covering part of the load, 98.6F mamalian occupants picking up some more (on the order of 225-250 BTU/hr for a sleeping adult human), etc. For a 2x4 framed house with a bunch of single panes the balance point will typically be 5F below the setpoint, so if you wanted to do the math assuming 63F have at it, but it won't be a huge difference for the +15F load.

But using Norfolk's 99% outside design temp of +24F will shave more than 10,000 BTU/hr off the calculated heat load, so the current boiler is really more like 3x oversized, an all too common condition.

A more cost effective approach to window upgrades would be to fix up the weatherstripping on the existing single panes, and install low-E exterior storm windows. Tight hard-coat low-E storms are $50-75 more expensive than a cheapo clear glass storms, but they raise the net performance to about that of a code-min replacement window, at a fraction of the cost for the window, and even smaller fraction for labor. Storm windows DEFINITELY pay off, and low-E storm windows pay off quicker than clear glass, despite the upcharge for the low E glazing. The tightest storm windows in the biz are Harvey Tru-Channel, but they are primarily a northeast US vendor. The low-E Larsons sold through the box store chains aren't bad, better if you upgrade from their bottom of the line versions, which are more air tight, and have nicer hardware, etc.

From a comfort point of view the difference beween naked single panes and single panes + low-E storms is pretty huge. With the former the surface temp of the glass will be below 60F whenever it's below 50F outside, with clear glass storms that doesn't happen until it's freezing, but with low-E storms or a U0.35 replacement window the interior surface of the window is still above 60F in a 68F room even at your 99% outside design temp, not hitting 60F until it's about +15F outdoors. It's a difference you can easily feel with your eyes closed, even when it's 40F outside. With the higher surface temps you also don't have nearly the magnitude of cascading denser cool air falling down the surface of the windows creating a draft.