Short cycling on DHW side of Quietside DPW-120

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  #121  
Old 10-04-14, 01:06 PM
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rd543759, pretty funny that you cite your wife's complaints because that is why I was originally "motivated" to address supply issues prior to getting to this point. We're better off that I did, but listening to her in the morning definitely helped move things along. I guess like Seinfeld said, most of the incredible things that our civilization has accomplished were done to impress women (of course the married version of "impress" is usually "get them to complain about something else").

I agree that the recommended tank would probably work better but I can't find it anywhere either. And even if removing my tank improved performance I would still be pretty disappointed that I wasn't using something I paid for. The prospect of buying a different tank to solve my problem does not excite me.

Repiping is fairly straight-forward. I would be doing it myself so I'm only dropping ~$75 in parts. And as mentioned I plan to install an anti-scald/mixing valve anyway. I have a pex tool, crimp rings, solder, flux, propane, etc...everything I need so it's not a big deal. It's frustrating to know that I'm most likely going to be dealing with the same problem, but being able to switch between direct and the tank gives the advantage of flexibility and puts the onus on tech support to come up with a different solution or admit a design flaw.

You weren't comfortable trying to call for DHW at the min fire setting (DIP switch #5 ON)?
 
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  #122  
Old 10-04-14, 05:56 PM
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Why are you not comfortable trying to call for DHW at the min. fire setting (dip switch #5 on )?
 
  #123  
Old 10-04-14, 08:20 PM
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I just didn't do it. Didn't see the point. I guess I will just to be sure its firing at minimum rate, as I can see how fast the temp rises at low flow with switch ON and OFF. I will get back to you with results.
The ONLY thing I'm having troubles with is the dishwasher makes it short cycle one time as it fills. I did testing, and the dishwasher draws a total of .79 gallons over 59 seconds. I could increase my line size to reduce pressure drop, which would increase flow rate a little bit, but not enough to keep it from cycling as the pressure would only increase a tiny bit, and I need about 2 times the flow rate. I'll keep playing with this and let you know if I can get it to work somehow.

I'm guessing I'm gonna have to deal with the short cycle issue on the dishwasher, and wash clothes in the HE washer on cold as much as we can. One time on the dishwasher every other day is a LOT better than the 10-15 cycles every morning during her shower.

I know how you feel about not using something you bought, or buying something additional to try to make this ill-engineered boiler work properly. Sometimes you just want to "cut the cord". I am simply using all the free to under $10 tricks I can think of…. when it craps out its done and I will replace with HE tank type heater. But I hope by lowering cycling, who knows, maybe I get 20 years out of it??? Maybe 2 years. Maybe 5 more months. You are the ONLY person I know that owns one
 
  #124  
Old 10-04-14, 08:42 PM
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I think they hide this info because by the time a consumer looks at the cost of the boiler itself, then the tank system, the stainless steel pumps, plumbing, possible labor if hired install, it adds up to $3000 in materials alone.

For a set up like that... 8 k in NJ...

Well if you're burning natural gas, how long will it take to recoup that, if you can get a standard water heater for $400,
IMO you wil never be ahead......


I'm sure my payback period will be close to ten years
Never... you will replace the unit before then. And most likely with a tank unit...

I know how you feel about not using something you bought, or buying something additional to try to make this ill-engineered boiler work properly.
In my experience anyone that spends money thinks its the best. and will say that regardless of how it performs. They need to justify the money spent. They assume they made the right decision... Its rarely true.... Usually they have to fool the wife....
 
  #125  
Old 10-04-14, 09:05 PM
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I will be the first to shout if I feel I got hosed or duped. My parents needed a new water heater. Mom wanted to go tankless because she paid the gas bill and water bill (town dwellers on natural gas like me).

I informed my Dad that even if we did the work ourselves, it would be a lot of work and expense. New venting even with PVC, after fittings for two lines will push $100. Especially if you pay for nice outside terminations. The boiler itself is about $800 for a cheaper one. More than likely need a bigger natural gas line plumbed in to deliver enough flow to run boiler properly.

They would have to deal with finicky nature of boilers themselves. "cold sandwich". HE washing machine won't work (not an issue since they've needed work at 10 years old, dad replaced with old school models). Dishwasher might not have enough flow to get boiler to even fire to deliver hot water.

All of this to "maybe" save money in the "long run".

Instead, me and Dad got a $400 heater. Hooked it up ourselves in about 20 minutes. Hot water, no drama. Let's say after 10 years his tank finally costs more to run than tankless. Is it worth the pain in the ass to deal with EVERY DAY to save (what… maybe $20-40 per year.. who knows?) That is like one restaurant meal for the pair of them.

99% of people, including me, want efficiency. Cost efficiency. Not necessarily energy efficiency. If they can make an energy efficient boiler cost efficient, that would be great. I just don't think they're here yet. Maybe in Europe. Maybe U.S. in 10 more years?
 
  #126  
Old 10-06-14, 09:53 AM
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Question for original poster

didn't mena to hijack the thread with my rants.

Have you had any luck yet? Bypass storage tank, set temp to 98f, see if it helps your short cycling?
 
  #127  
Old 10-06-14, 08:43 PM
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Rant away rd543759. By all means. Personally I want cost and environmental efficiency and I'm going to be pretty disappointed if I have to replace a second Quietside less than 10 years after installing it (my previous QVM9 had to be replaced on pro-rated warranty after 7 years...leak in the primary heat exchanger). I'd eventually like to get a wood gasification boiler and keep the gas for a backup, but from what I've read you need something like a 1000 gal buffer tank to optimize performance. Certainly sounds like a lot of work and additional complexity.

At this point it sounds like it's probably not a simple setup or piping issue...so I haven't made it a priority to repipe or do additional testing. Maybe if my wife cared about the boiler's performance anywhere near as much as she does scalding hot showers I'd be getting that extra bit of motivation.

Speaking of which, does 98F make for a nice hot shower? If not I won't be getting to test that one out in this household until the weekend. And I'm confused about how that would stop the short cycling. Hasn't the running theory been that the DHW loop can't pull enough heat away from the primary via the plate to plate heat exchanger?
 
  #128  
Old 10-07-14, 05:49 AM
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as the approach temperatures converge, less heat is transfered.
A seemingly small brazed plat e with boiler water at 180 and in a radinat floor application with a design water temp of 100 will transfer a hell of alot of BTU compared to a DHW (with storage) application with a DHW water temp of 140.
Since your boiler seems to modulate at 140, really the best you can do is try for a 10 or 20 degree difference in approach temperature.

Now if you want to repipe the boiler, then you could install a bigger plate that would handle the close approach better.
 
  #129  
Old 10-07-14, 07:28 AM
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Previous poster hit the nail on the head … if I understand it right. By lowering outgoing temp, I am in effect making my boiler less efficient, by how much I'm not sure. I am on the edge of short cycling showers.

I still haven't set dip switch to minimum fire and had a shower yet, still need to test that.

I also wonder, if you set your boiler to keep temp at 120F, it overfires and overshoots, then has to shut itself off. Maybe by having the temp set lower it modulates lower as well?

At higher temps the "brain" wants to get that water to 120 right away, then realizes that its overshooting, but can't modulate low enough to bring it back down, and has to shut off.

At 98-102, in my case, it must keep the fire rate lower because it knows it doesn't have to make the water as hot.

It could be as simple as the heat transfer rate will temps converging, lowering efficiency.

A person would need an accurate flow meter on the gas line by the boiler to test the gas consumption with different settings. In my case, even though you set the boiler to 98F, at a shower flow rate of 2.5 GPM, it still gets plenty hot for a shower. I have to run cold as well. I don't think it would hurt to hit some buttons and give it a go.
 
  #130  
Old 10-08-14, 09:17 PM
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I set my DHW temp to 98F tonight. Ultimately I saw the same short cycling behavior but here are some details...

I came home tonight and planned to take a shower with the DHW running "direct" (tank isolated but supply still running through circ and BFP into the DPW) and the temp set to 98F. When I went to change the temp I saw that a zone was calling for heat so I waited a bit since I didn't want anything else going on while testing. After about 10 min I got impatient and shut off that zone. With the tank isolated I set the DHW temp to 98F and turned the shower on. I got nothing. The DPW did not fire. I waited a while and still nothing. No hot water. I bumped up the temp bit by bit until I was back up to 140F and still nothing. Then I turned on the kitchen sink's hot tap and it fired. Upon firing it short cycled but it was not nearly as bad. More of a 45-60 sec on/4-6 off. So I shut all the taps and dropped it back down to 98F. I tried running with just the shower and it kicked on this time. It began cycling 4-6 sec on and 3 sec off similar to what I saw when I ran direct previously. Incidentally, rd543759 you were right about the 98F setting in terms of comfort, full hot with it set at 98F does still require some cold added to be tolerable. So I shut everything off and put the tank back into the circuit. I set its aquastat to ~80F (not a very precise knob on that thing) and ran several hot taps to get the tank down to the set temp. It came on after several minutes and short cycled as it has been, 12-15 sec on/3 sec off. I left it set like that and took a shower that felt no different than when I had the DPW set to 140F and the tank to 120F. I see no reason to keep the DPW at 140F and the tank at 120F if showering with them set to 98F/80F is fine so it's still set that way.

I still need to give the DIP switch #5 a try but need to get some sleep.
 
  #131  
Old 10-10-14, 02:36 PM
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Glad to see you're getting results. I don't think our temperature gauges are accurate. I think if you have enough flow it will get down to 98F, but otherwise it will modulate as low at it can to keep the temp as close to 98 as it can… In my case my incoming water temp is high enough that the boiler can only modulate low enough to give me about 105F shower water, but I have enough flow and BTU draw to keep the heat exchanger from getting too hot, forcing a shutdown. If you're not flowing enough and the heat exchanger gets above a certain limit, it will shut off the boiler.

I'm hoping if we get enough owners fighting these gremlins, somebody will have an AHA lightbulb moment and give me a cheap, simple solution to some of the short cycling issues with certain appliances/low flow rates, etc.
 
  #132  
Old 12-02-14, 07:15 PM
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Pretty old post I know, but I have an update. I piped the DPW's DHW inlet direct from the supply as suggested by customer service and saw the same exact short-cycling that I was seeing when I ran "direct" prior to re-piping (by isolating the tank as best I could).

I configured it so I can run through the tank circuit or direct and took the opportunity to install and anti-scald/mixing valve. The mix valve has worked out nicely.

I have yet to try the max fire (DIP switch #5) experiment.
 
  #133  
Old 12-03-14, 07:41 PM
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Tonight I observed the DPW as a bath was run with the piping configured to run DHW via the tank circuit. The tank's aquastat is set to 110F and the DHW on the DPW is set to 130F. Once the tank started calling for hot water the DPW stayed on for ~3 min straight and then shut off for a few seconds and then fired back up for 2 min and then off again and then back on for a minute and a half or so. I think it went off and then fired for one more minute and a half cycle before the tank was satisfied. This is the first I've seen this. I don't know what qualifies for "short-cycling" and I would still expect the DPW to just run flat out until the tank is satisfied, but this was the most stable DHW performance I've seen by the unit.

Is there any chance that a colder incoming water temp is creating a bigger differential for the DPW? If it has to dump more heat to overcome that larger differential and get the incoming water up to temp then maybe it's less likely to bump up against the high limit?

Also, the last line of my previous post should read "I have yet to try the MIN fire (DIP switch #5) experiment"
 
  #134  
Old 03-13-15, 02:23 PM
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Keeping the thread alive

I've been gone for a while. Replying to last post. What you see is exactly what I see with my unit. Running a bath, and lower incoming water temps, finally give you enough Delta T to keep the heater running. You are right on the edge of having it run constantly with no cycling. More water flow, colder incoming water temp, or a hotter bath temp would probably keep it running.
My boiler has been fine over our Iowa winter. It only short cycles during laundry and dishwasher. As weather gets warmer I'm sure the wife's cool showers will cause the cycling.
Quietside's newest boilers will modulate down to a lower rate, so we probably aren't the first people to have this issue. I was so concerned about MAX BTU, that I didn't give a thought about the MIN BTU that the unit could deliver before shutting down to save the heat exchanger.
I would rather fill the tub slower, or use lower flow shower heads, than to have to worry about my boiler giving out because of the on/off nature.
I think the only way to fix our boilers is to do what Quietside did, and make them modulate to a lower BTU output, but I'm sure this is cost prohibitive, unless we could buy valves, and maybe a motherboard designed for a newer unit, and put it into our boilers.
 
  #135  
Old 03-13-15, 02:36 PM
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Recall

More important. I just found out there is a recall for these boilers, fire hazard. I found out by accident, not by phone or through the mail. Be proactive. Google Quietside recall. Challenger Supply, etc.
 
  #136  
Old 08-13-15, 09:04 PM
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Have meant to check back on this many times and have failed to do so. Thanks for the insights and observations. How did you find out about the lower modulation on the newer units and the recall? All I could get from Challenger Supply customer service (and I've probably gone over this somewhere in this thread) was insistence that my flow rate was insufficient.

Thanks again and sorry for the radio silence
 
  #137  
Old 11-18-15, 10:42 AM
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Recall

I think I was looking up specs online for my boiler, and I saw the recall notice. I never registered my unit, otherwise I probably would have got something in the mail.

I saw a newer model unit at Menards, and I noticed the BTU range on the low side was much lower.

To my way of thinking, our units were not designed with the buyer in mind. People that want efficiency are usually cheap, tight, frugal. So making the boiler able to operate at a lower range, for lower gas usage, and lower water usage, would have been a VERY smart thing to do right off the start.

Instead, to keep the boiler happy, we need to burn more gas and use more water. However, I think it is smarter in the end, to use more gas and use more water....than to let our units constantly cycle. So far my boiler is still working. Probably going on 3 years now.

In my case, I need to do some more math. My cities electric rate is so high, and my natural gas rate is so low, that when the boiler fan runs, my electric usage probably trumps any kind of natural gas efficiency improvements that the boiler saves me.
 
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