Intellidyne HW+ Setup

Discussion in 'HVAC Heating & Cooling' started by Gary in NJ, Sep 12, 2018 at 7:38 AM.

  1. Gary in NJ

    Gary in NJ Member

    Joined:
    Apr 11, 2010
    Location:
    NJ
    I have an older boiler that is 3x oversized for my heat load and Dana suggested that I install a heat purging boiler economizer control on my aquastat to help with short cycling and gain some efficiency from the system. I purchased an Intellidyne 3250 HW+. Installing the controller took all of 10 minutes. It's as simple has connecting the unit to the hot and common for power, and then removing the wire in the aquastst that controls the burner and jumping to the controller. It took me as long to type this as it did to perform.

    I do have a few questions regarding set-up.

    Currently my aquastst is set for 187F. I'm quite sure I had it set to 180F, but I did have a service performed last winter and my guess is that the tech "up'd" the setting. Sure enough, the boiler shut down right at 187 (confirmed with the temperature gauge and an infer-red) and the temperature continued to climb to about 195. From an efficiency stand point I assume that I'd want the boiler to run hot (it's a WM Gold P-WGO-4 Series 3 and is safe to run to 210F). If I set the HLOLIM at 140F that would give me 55 degrees of purge to circulate before the HW+ releases the boiler to fire. I'm I thinking about this correctly?

    Regarding Pre-Purge, my first check of the system was when the boiler had sat idle without firing for a few hours. The water temperature in the boiler was 140F. After the call for heat it took about 110 seconds for the circulator to engage and the boiler fired about 10 seconds after that. Was my pre-purge period 110 seconds, 10 seconds, or 120 seconds? I did a second test with the boiler still at 170 degrees. I cranked up the DHW to force a call. The circulator engaged about 60 seconds later and three minutes later I gave up waiting for the boiler to kick on as there was plenty off hot water in the system too meet the demand - the boiler never kicked on. So what exactly is pre-purge? What is the best test to determine the correct setting? Why the 50 second difference between the first and second test?

    Regarding the DHW sensor, my hot water is set to deliver 140F. The directions for the DHW sensor say to install the sensor on the out flow pipe, which I did. The directions state....

    "This parameter is used by the controller to set the low-limit temperature for the domestic hot water. When the domestic water temperature goes below this setting, “HEATING/LOLIM” will be displayed, and the controller will no longer attempt to achieve any savings and return control to the operating-control. To change this setting, plug the sensor into the appropriate jack to increase or decrease the value. The indicated value will be what is currently set in the controller (default = 120˚F / 49˚C). The range of adjustment is between 90˚F/32˚C and 180˚F/82˚C. Remove the sensor when the desired value is reached."

    I ran my hot water at the sink for 5 minutes and confirmed that it was at 140F with the I/R. I then went to the outflow pipe and measured just 107F where the pipe leaves the tank. My guess is that the actual water tank is much lower in the enclosure, so by the time it exits the enclosure some heat has dissipated. So what would be the proper DLOLIM?

    Thanks for any help.
     
    Last edited: Sep 12, 2018 at 10:27 AM
  2. Gary in NJ

    Gary in NJ Member

    Joined:
    Apr 11, 2010
    Location:
    NJ
    I think I can answer my pre-purge question - my system doesn't have a pre or post purge feature. The ten second period I was describing above is simply the Honeywell R7184U checking that the igniter is firing and a flame is present.

    I am confused as to why it takes so long for the circulator to start pumping after the call has been made to the aquastat.
     
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  4. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    The raw combustion efficiency is a bit higher and the standby & distribution losses are lower at low temperature. You're making the trade-off between those factors and the extreme losses of short-cycling. Having 55F of temperature headroom to slew through guarantees fewer ignition cycles and longer burns, which is what the goal is. So raising the high-limit to the max gives you the greatest temperature swing, longest burn time.

    I'm not sure why there is a delay on the circulator on call for heat. I'd have to understand the whole control scheme to figure that out. The default pre-purge setting on the Intellicon is 0 seconds, but the time from the call for heat for until the burner fires is the actual pre-purge time, and it can be set by following the instructions starting at about 2:40 in this video.

    The pre-purge time is a delay to allow any interlocks from automatic flue dampers etc to settle, but I believe the circulator should be running during that time. Time 0:00 on the pre-purge should be when the call for heat starts, and for most oil-burners with just a barometric flue damper a zero pre-purge time is appropriate, since the burner would fire right away if it were at the low-limit.

    IIRC all WM boilers an Energy Star label all have an electrically operated flue damper that takes several seconds to fully open, but there should be an interlock in the controls that suppresses firing until the open flue is proven by (I believe) a small switch in the flue damper unit. If the contacts or relay power to/from the damper are getting flaky or intermittent it may explain odd delays. When operating with the Intellicon in place damper may or may not open as soon as there is a call for heat, whether the burner eventually fires or not. Some boilers will normally delay the firing for several seconds after an initial call for heat (don't know about this one), and if that's how yours operates add that time into the pre-purge if you need/want better accuracy on the accumulated savings reported. But a pre-purge time north of 100 seconds would be rare if everything else was working properly.

    When the boiler's temperature drops the programmed low limit temp during a call for heat with the circulator running it will fire up, which would explain why the burner fired 10 seconds after the circulator started when the boiler had been idling at 140F, and why it didn't fire at all on the second pass when it was idling at 170F and satisfied the call for heat before reaching 140F. ( Congratulations- you avoided an entire burn cycle AND it parked the boiler at a lower temperature, for lower standby loss! )

    The sensor needs to be insulated and as close to the tank as possible, with 100% of the pipe between the sensor & tank insulated. If the water in the tank is really 140F and you're measuring 107F something isn't right. There's no way it's dropping 33F in just a few inches of pipe. If you're taking the temperature measurement with an IR thermometer on bare copper pipe it will read dramatically lower than reality due to the very low IR emissivity of copper. A spot of spray-paint (any non-metallic color) on the pipe where you're taking the IR measurement would give you a more accurate read. This is an issue with aluminum and bright galvanized ducts & plumbing too.

    The DLOLIM should be set a 5-10 degrees lower than the tank's aquastat setting. The sensor tells the controller to not suppress firing even if if the boiler temp hasn't yet dropped to the heating low limit yet so that the hot water service is maximized. With the heating low limit set to 140F and the indirect's aquastat also set to 140F you may have issues with getting enough hot water. It's hard to heat a tank of water to 140F with 145F water being pulled from the boiler through the heat exchanger, but you can still get good heat transfer from 145F heating water in the indirect if the tank's storage temp is set to 120F.

    More recent code fore new installations usually requires hot water that goes to sinks & bathing to be tempered to 120F or lower with a tempering valve or thermostatic mixing valve. (It's still code-legal to send hotter water to dishwashers and washing machines, but not to sinks and showers.) If there is a tempering valve the sensor needs to be on the tank's outflow, not the tempering valve's outflow pipe.
     
  5. Gary in NJ

    Gary in NJ Member

    Joined:
    Apr 11, 2010
    Location:
    NJ
    Dana,

    You were correct, the I/R was not reading the copper pipe correctly. The DHW sensor is spot on show 140+ on the output. I set the DLOLIM at 130F and the HLOLIM at 145F. For now I'm keeping the pre-purge @ 000 seconds.

    I still don't know why it takes 120 seconds for my circulator to kick in. Could this be a setting on the aquastat? I can't find anything in the Honeywell documentation that describes a circulator delay. As soon as the circulator engages the HW+ goes from "Standby" to "Econmizer" mode so it's all communicating correctly.
     
  6. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    I guess the real test will be during the heating season when you can time the burns, and count how many burns are missed. In an ideal world the minimum burn time would be 10+ minutes, but you don't have enough thermal mass or zone radiation to hit that.

    You might look through the boiler manual to see if they spec a smaller nozzle size and down-size with a smaller nozzle at the next tune-up, which would help. Usually down-firing by a large amount will give up a percent or two in maximum achievable combustion efficiency, but if it increases the minimum burn time on zone calls from 3 minutes to 4-5 minutes it'll still be a net savings.

    I'm not sure how low you can really go- the WGO-4-RD (reduced input) has a DOE output of 123K to the WGO-4's 145K (a 1.00 gph nozzle instead of 1.20 gph) and a higher AFUE. It's the same boiler underneath, but with a smaller nozzle and an electric flue damper, so whatever nozzle they spec for the -RD would be a safe start, extending the burn times by about 18%, and (if tuned properly) a 2% improvement in raw combustion efficiency. The combination could add up to a 3-5% reduction in fuel use compared to keeping with the nozzle specified for the WGO-4. The nozzle part numbers that can be used would be specific to the burner unit (Carlin, Riello, & Beckett burners have all been shipped with this boiler).

    It also looks like some burner specs define a pre-purge time. eg: In Table 1 the Carlin manual calls out a 10 second pre-purge & 10 second post-purge on the primary burner controls for their model 60200-02.

    I'm not sure adding the electric flue damper to make it look exactly like the -4RD would be cost effective, but the damper might be worth at least considering, since you seem competent to perform a DIY installation (which seems like you might be.) The smaller nozzle is essentially free, since it's normally replaced every few years anyway, but the damper, not so much. Whether the damper ever "pays off" as a retrofit is a bit harder to tell.
     
    Last edited: Sep 14, 2018 at 2:53 PM
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