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Pump speed control - How do you guys do it?

Until a couple of years back, a heating circulation pump was a simple-enough thing that everyone fitted and forgot.  Thanks to clever design going back decades, such as water-lubed beaings and glandless cans that cannot leak and keep water away from the electrickery, they've become staggeringly reliable and long-life.  A few years back, the pump in my childhood home was eventually retired, still working, after more than 40 years.



Then suppliers realized that fixed-speed pumps were not ideal when the dynamic head in the system changes (motorized valves, thermostatic radiator valves, ...), and electronically-controlled pumps came to market.  Benefits: lower power consumption, reduced noise, ....  Most of these work by counting rotor revs and measuring power consumption, then calculating (based on the impeller design, etc) the probable output volume and actual load.  Actually, VERY cunning math, all done with no actual pressure or flow sensors.  In some cases, there's a water temperature sensor, so the pump automatically throttles-down during the periods when the furnace is off or on reduced output.



At the same time, in Another Part of the Forest, high-efficiency condensing furnaces came on the scene, to save energy in a different way - and in some cases, changed the Pump Game completely!  Previously, design objectives were to limit the Delta-T across the boiler to a maximum of 12C (23F degrees) or so, and to keep the Return temperature above 60 degrees (140 F degrees) to prevent condensation and 'back-end rot'.  But for a condensing boiler to condense, a reasonable area of the heat-exchanger (or most of the recuperator) needs to be below 56C degrees (133 F degrees).  At the same time, the maximum permitted delta-T Flow/Return increased to maybe 16 or 18 C degrees, so that a furnace can deliver heating water at (say) 70C degrees and still be in condensing mode with the Return water at 52 C degrees.



For a 'system' boiler incorporating a modulating pump - no problem.  The furnace's own software can manage the burner rate and the pump speed, so that the correct heat output and optimum Flow/Return Delta-T are both maintained.  But there are many furnaces on the market in Europe that do not have an inbuilt pump, or have a pump with a coarse modulation method (eg. just 3 fixed speeds with the furnace controller selecting the best-fit).  If the requirement is multiple burners on a common header, then keeping the Return temperature optimal is tricky.  The electronic pumps, even with temperature sensors, are not ideal as shunt pumps.  What's needed is a variable-speed pump modulated by the delta-T Flow to Return.  Variable-speed pumps do exist (eg. for solar panels) but I've yet to find a suitable controller able to accept two sensor inputs and provide a varying PWM output for the pump according to the temperature difference. 



What do you guys use for shunt pumps between multiple burners and a shared header?
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Comments

  • Pump Speed Control

    Couple of thoughts on this...



    Assuming the application is a "shunt" or circ dicated to an individual boiler (this combination supplies BTU's into the primary circuit that has it's own pump), although we have a lot of ECM pumps installed in this manner working fine I have wondered if there is a concern that the boiler and shunt pump have seperate brains.  However, it makes sence that if there is an increased demand the boiler's firing rate goes up and, due to the increased demand the pump speeds up at the same time.  To date we have not had any complaints with ECM on Mod Con boilers (after 4 years of selling these in the USA).



    Technically speaking, probably best to use a boiler control with a PWM output and modulate the pump flow with the boiler firing rate.  Delta T is a "it depends" question.  Is there outdoor reset?  What effects the boiler firing rate?  Is it a high friction loss heat exchanger?



    Today there are a number of larger boilers that use a modulating gas valve that has a 0-10Vdc signal modulating the combustion air fan - and this same signal can modulate the RPM of an ECM pump - waaaay cool.  500,000 BTU is 50 GPM, modulate down to 100,000 BTU is 10 GPM - extremely simple control.



    Looking at the primary loop, what we have found is for condensing apps, control the return water temp to assist condensing (and of course the opposite for non-condensing boilers).  Adjust the speed of the BTU train (thanks Dan - this is a great analogy).  But again this can be an "it depends" answer (for example, is there a hydraulic seperator in the system?).



    Regarding system pumps, delta T only works if each zone is relatively the same size (this is why differential pressure control is by far more common).



    Hope this helps...  It's not overly complicated actually - mostly common sence.
  • croydoncorgi
    croydoncorgi Member Posts: 83
    edited November 2011
    Header = Hydraulic Separator!

    Thanks Steve, for your thoughts about this.



    In fact, my current problem is 2 boilers with fixed speed shunt pumps both connected to a hydraulic separator. I used the alternative term (header) - 2 nations divided, etc. ;=)



    When the heating load is quite light, there will be only one boiler runing and the fixed-speed shunt pump works at a higher rate than the (electronic) main circulator.  So hot water whizzes through the separator and back down the boiler Return, and the delta-T gets too small.



    Easy to understand the problem - but finding a solution is tricky.  I suppose some sort of differential pressure valve would do it.....but I was hoping to have a bit of fun with thermisters, a microcontroller of some sort with PWM output and a PWM-controlled pump.  Does Wilo offer such a thing??
  • PeterNH
    PeterNH Member Posts: 88
    This might be it

    I believe you might be interested in these pumps:



    http://www.heatinghelp.com/files/posts/10062/Taco%20OOVDT%20Circs.pdf



    Peter
  • hot_rod
    hot_rod Member Posts: 21,862
    got a drawing of that piping?

    This is a common method, shown in Caleffi I-dronics 1, to pipe multiple boilers into a separator. The boiler pumps are controlled by the processor in the boiler.



    Another option might be a solar ∆T control. It can be used as a ∆T or setpoint control. It is not a PWM but a triac relay that pulses the voltage on/ off very quickly. A poor mans variable speed :) It works on any small wet rotor circ with a draw of 1 amp or less.



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • croydoncorgi
    croydoncorgi Member Posts: 83
    edited November 2011
    Pump modulation methods

    I looked at solar controllers already - and got a bit confused!  Several of them seem to use a standard pump, presumably as you suggest with triacs or somesuch 'chopping' the AC.  The result can be a bit rubbishy!  At certain speeds the pumps tend to growl and/or resonate as the coils and rotor get put in modes the designers never intended!  More up-market solar systems use pumps with PWM speed control - but these pumps are harder to get and much more expensive.



    Anyone tried a PWM pump on a heating system?  How? Why? What results?
  • hot_rod
    hot_rod Member Posts: 21,862
    no doubt

    the triac speed control does cause the pump, and any un-supportrd piping to pulse. We have probably 500 or more out there connected to Wilo Star 16 pumps with no adverse effect to the pumps. The only pumps we get back are the ones installers try to pump just air with :).



    The more expensive BX and MX solar controls have the PWM signal as well as the triac. It does add cost and there are not many, if any small wet rotors on this side of the pond that take that PWM signal. So the extra cost of the control and a more expensive pump, maybe not worth it for a solar pump?



    I do have a Grundfos ECM, Solar PWM pump to try out, it's a Euro model and 230V however. I have it connected to an I-solar BX control and it runs very smoothly.



    There are many ECM and PWM pumps made by Grundfos for the OEM market. The US market is so price sensitive, tought to sell high efficiency for a small solar pump.



    Here is a picture from the Grundfos booth at the InterSolar show in Munich a few years ago. They had two displays like this with unique, high efficiency solar pumps.



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • croydoncorgi
    croydoncorgi Member Posts: 83
    edited November 2011
    More developments!!

    Thanks for the feedback about ECM and PWM pumps.



    As luck would have it, I was called out to a fault on a very similar boiler to the oneswith the pumps I'm trying to tame.  I had to remove the pump to get at something else, and found a strange thing!  The boilers are part of a range that have common controller hardware and wiring loom.  These were from the cheaper end of the range and come with a fixed-speed (Grundfos) pump.  The wiring to the pump therefore has 3 cores: Live, Neutral, Earth - ie. Ground). But when I pulled out a connecting plug, the mating socket had FOUR holes, with 4 wires connected.  I reckon the fourth wire is a PWM connection from the controller.  My speculation now is that the software in the controller IS quite possibly  sending out a PWM signal  - but with no result since the pump is fixed speed.  The boiler would still work 'OK' but moved into the Cheap Seats economy-wise.  I guess I'll have to get a digital mini-scope and see if there's PWM on that wire, varying according to burner rate etc.  Based on a general principle of software design and build - that you only do it once, if possible, rather than twice -  I may be in luck.  I did ask the manufacturers previously about putting on a PWM pump and was told 'impossible'.  But maybe the guy I asked just assumed this because he'd never met the couple of guys who did the software or, if he had, they never discussed what they'd actually done in detail....!  I live in hope!
  • hot_rod
    hot_rod Member Posts: 21,862
    yes I can

    often times the Euro pumps we get have 4 pin power cord sockets. Usually the pump power is H, N and a ground (3 wires)



    A PWM would require two more. The PWM leads or terminals are usually a much smaller gauge wire, more like a thermostat type wire.



    Didn't one of the Viessmann Vitodens have a variable speed, PWM boiler pump onboard?



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • croydoncorgi
    croydoncorgi Member Posts: 83
    Viessmann and other boilers with mod. pumps

    Yes - you're correct - Viessmann supply various pump options across the ranges of boilers.  Don't know the US 'marketing' name is  but what's referred to in UK as the Vitodens WB2A and WB2B can both have (externally-mounted) modulating pumps.  Has to be said, however, that historically reliability was a bit of an issue!  Can't really blame Viessmann 100% - they don't in fact make pumps. Maybe just poor choice.
  • PWM Circs

    Here's the deal...



    Pulse Width Modulation simply means modulating the width of the electrical sine wave by "chopping" the sine wave of the power to the motor.



    It is either done externally (Tekmar have been doing this for years - with injection circs) or via an integrated circ controller.  Most (I think all) small, standard "non-ECM" circs from all manufacturers can run on PWM (WILO for sure)



    To be honest, I am not a huge fan of PWM as below 30% capacity the circs's life is shortened and they have a tendency to get noisy.  But back in the old days that was the most (and only) way to vary the flow in these little guys.
  • NYplumber
    NYplumber Member Posts: 503
    Variable

    Hey HH, stepping in here, but not sure I can be of help.



    Viessman and iirc some Lochinvar knights have built in pwm for the boiler circ on their controller. Incorporating an outside controller whether it be a Tekmar, OO-VR circ, or other controller may cause nuisance lockouts due to the boiler and control not talking to each other. When incorporating pwm with a modcon, super efficient low modulation is acheived. All this adds to the cost of the boiler install, usually the ho doesn't see it necessary thus your install price seems unjustified & outrageous. Not to mention it adds complexity to an already complex set of controls, more to go wrong, difficult to diagnose.
    :NYplumber:
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Which

    Viessmann boiler do you have and if multiples whose LLH? Do we have a sensor in our LLH? I could ask many questions. Did we use the 143 plug, ie external demand? All Viessmann recommended pumps are based on maintaining a 40 degree delta across the boiler on Vitodens. Current model in the US is the same WB2WB as across the pond.



    If using multiple Vitodens and no cascade there should be 2 LLH sensors with boiler one set at one curve and boiler two at another. You loose the cascade ability by not using the cascade control so you can move more flow then what is needed.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • croydoncorgi
    croydoncorgi Member Posts: 83
    NOT Viessmann!

    The comments about Viessmann and modulating pumps were a by-the way!..  My boilers are not from Viessmann and actually have (inbuilt) Grundfos pumps.  Which is of course a major factor - if they were external I could down-size them much more easily.



    My other comment about Viessmann is that you're generally OK if everything has a Viessmann badge on it.  For example, on another job I discovered major limitations in the way the '143'  connection works.  In that case, I was trying to remediate someone else's attempt to integrate Viessmann and Honeywell Hometronic (a multizone control system with individual radio-controlled radiator valves).  Deceptively simple issues such splitting the demands for hot water reheat and space-heating and persuading the boiler to switch OFF its pump (noise issue) were not simple at all.



    On this side of the pond, there is a distressing trend for control 'Walled Gardens'.  Unless you use branded controls from the same supplier as the boiler, it all gets problematic and gnarly.  But if you DO use branded items, then you may find yourself cast in the role of Mickey Mouse!  In many cases, you end up with more cost and fewer control options.  Unfortunately, the European Commission also left some unintended consequences (??) in the 'Energy Using Equipment Directive', which made Walled Gardens easier to justify against monopoly criticisms.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited November 2011
    143

    The external demand or 143 plug is not meant to be a traditional "TT". I often see its use not applied correctly as in exactly your case. External demand should only be used in my opinion when you have a high temp source such as a HX for a pool or snowmelt where you want to maintain a fixed setpoint. You turn a smart boiler into a dumb boiler when using external demand. You must tell it what to do on the demand.



    I don't think internal boiler controls are as much of an issue as the issue of contractors not understanding how they work. If I wanted to use outside sources for system control I would make sure my boiler control was 0-10vdc capable and can easily intergrate controls by others to run my system without taking away the boilers firing logic. In the end its a matter of system design and equipment selection that fits the application.



    Internal boiler pumps are sized to move the boiler required gpm across its heat exchanger. Sounds to me like you probably have an oversized boiler which is causing the problem not the pump. Pump is doing its job.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • croydoncorgi
    croydoncorgi Member Posts: 83
    Actually, not the case!

    Hate to disagree with you, but.....



    "The external demand or 143 plug is not meant to be a traditional "TT"."

     I didn't specify the boiler or the Hometronic system. I just got the job of mating porcupines!  Given the use of the weather-comp boiler insert, I don't see why you would think that applying external demands to the boiler are 'dumbing it down'.  The only difference between Hometronic and a Viessmann room controller is that the Hometronic box doesn't speak KMBus, so apart from 143, what other option is there??  The basic requirement for a boiler with weather comp is to separate the demands for hot water reheat (80C Flow temperature) and space heating (Flow setpoint weather-comped, between 40C and 70C),  And, with the Hometronic producing a demand signal for the boiler only when necessary, it makes no sense to leave the boiler and pump running just to keep the pipes warm!  But that's what the dumb Viessmann control interface will do, unless you do a lot of tweaking and messing about.  Why, oh why make it so stupidly complicated??







    "I don't think internal boiler controls are as much of an issue as the

    issue of contractors not understanding how they work."

    Possibly true, distressingly often.  But as stated, I was trying to remediate a bad situation (originally with the boiler running a fixed temperature with external on/off control - so it never condensed!).



    "If I wanted to

    use outside sources for system control I would make sure my boiler

    control was 0-10vdc capable and can easily intergrate controls by others

    to run my system without taking away the boilers firing logic. In the

    end its a matter of system design and equipment selection that fits the

    application."

    Why would you only accept 0-10V (which Viessmann won't accept, AFAIK!)  Opentherm offers a far better alternative than 0-10; in particular the controlling equipment can actually get feedback about whether the boiler is actually working!  Unfortunately, Viessmann UK denies all knowledge of Opentherm, too.



    I also heard last week of a 'feature' that allows connection between Viessmann and KNX (a Eurpoean equivalent of BACNet).  It proposed to use the LON interface on the Viessmann side and then gateway from LON to KNX.  But then, after a lot of cost and complexity, virtually ALL the data went from Viessmann to KNX (boiler status etc.) with NO means to actually adjust setpoints, command the boiler On, etc., via KNX!!!  See what I mean about 'Walled Gardens'.  But I suppose they're essential to confine the lunatics!







    "Internal boiler pumps are sized to move the boiler required gpm across

    its heat exchanger. Sounds to me like you probably have an oversized

    boiler which is causing the problem not the pump. Pump is doing its job.





    "

    Wrong again, I'm afraid.  Domestic-size 'System' boilers sold in UK and elsewhere in Europe tend to have pumps sized for the 'typical' radiator system that matches the heat output of the boiler - in other words, unless they are the modulating type, they will be too big to use as a shunt pump.  It's usually 'commercial' boilers (output 50+kW) that have pumps sized to use as a shunt only - because the systems they will attach to will almost always have (an) additional pump(s) on them anyway.



    My reason for selecting two (domestic-type) boilers to heat my own house was because they were a VERY good deal in a run-out sale  - and I thought the pump issue could be fixed relatively easily by reducing their output with a triac chopper circuit controlled by the Flow/Return delta-T.  It still seems perfectly feasible....
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited November 2011
    Huh?

    Ok.. Please let me know if I miss something.



    External Demand..... Once you utilize external demand you are initiating a heating program changeover, blocking circulation pumps and burner and creating s minimum boiler water temp setpoint. You have effectively taken away the boilers firing logic as it pertains to the boiler ability to modulate water temp based on outdoor reset. Viessmann remotes via KMBus provide the boiler indoor temp feedback which the boilers uses in its calculation of supply water temp in connunction with odr. The other option is to let the LLH sensor do its job and tell the boiler to come on and go off. All you need to do is turn a system or zone pump on, we will fire if necessary.



    Now 0-10vdc. Its there because utilizing Tekmar or other controls capable of sending a 0-10 signal. They become the brain telling the boiler what supply water temp is needed so they effectively take control of the boiler without effecting the boiler firing logic. Tekmar is very common and it allows Tekmar installers to utilize their full gammet of indoor feedback controls. Taco I-Worx the same. We can also run LON and Vitodens 100 has OpenTherm.



    Lastly Vitodens is not a domestic based water heater its a boiler. I have plenty of Vitodens 200's doing commercial DHW only with indirects and they work like champs.



    Viessmann specifies UPS15-58s on the smaller boilers and 29-99's for the larger boilers all based on a 40 across the boiler. How else would I be able to move the btu's these boilers can make. The max flow rate for all the small boilers up to the WB2B35 is 6.2gpm.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • croydoncorgi
    croydoncorgi Member Posts: 83
    'way too much to disagree with!

    But just to take the first point at issue:



    You have effectively taken away the boilers firing logic as it pertains

    to the boiler ability to modulate water temp based on outdoor reset.



    The point of outdoor reset i to calculate a new setpoint based on whatever intial setting is in the boiler plus or minus an offset derived from the external sensor value and a compensation curve.  Viessmann's approach (in the Vitotrol 200, anyway) is interesting because it uses the 'Room Temperature' value from the front panel control to move the whole curve up or down.  So long as you don't worry about how it 'knows' what the room temperature is without actually having an indoor sensor, it works pretty well.  (It's not really 'Room Temperature' at all!  It's just a best guess based on typical heat-loss patterns.)



    But to say that putting an external demand on the boiler 'takes away' its firing logic is a completely new way of explaining how modulating boiler controllers work!!!  As far as I'm aware, the Viessmann controllers are no different from any of the others.  They mostly adjust the fan rpm to give n degrees temperature rise per minute towards whatever the setpoint is.  If the Return temperature rises rapidly (in the case of Viessmann, determined by the flue gas temperature, I believe, since most models don't actually have a Return sensor), the fan rpm and therefore the burner rate may also be backed off, to achieve an optimum Flow / Return delta-T.  However, the Flow temeprature curve has priority, so if there's a problem with the system that makes the Return get too hot, there's little the burner modulation logic can do: it will carry on up the Flow temperature curve and if the Return gets within s couple of degrees - tough!



    If the Flow setpoint is adjusted, the burner controller instantly recalculates the required fan speed to deliver a suitable temperature curve towards the new value.



    The neat thing about most modulating controllers, especially those with outdoor reset, is that the modulation curve is deliberately made very flat close to the setpoint, so that the burner will continue to operate at a low setting hovering right on the setpoint, rather than cycling on, off and on again as it overshoots the setpoint and then falls back past it again (but only when the Demand signal stays on).



    If you turn off the Demand signal to a boiler (even one with weather comp / outdoor reset) it should shut down.  Then, when Demand reappears, it should restart and recalculate a new profile based on twhatever Flow, Return and external sensor temperatures then exist.



    How could it work otherwise?



  • CMadatMe
    CMadatMe Member Posts: 3,086
    Nope

    I'll say it again. External demand means some type of heating circuit change over. When used you must set a target water setpoint temp. You are no longer utilizing odr. If will fire low and works its way there but not using odr.



    By the way fan speed runs independent of gas in the case of the WB2B.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • croydoncorgi
    croydoncorgi Member Posts: 83
    Please check your facts

    Boiler in that case was a WB2A.



    I don't know full details of combustion process on WB2B but from my previous work in combustion are of WB2A and Vitdens 300 series machines, ALL have previously used the fan RPM to control the burner rate.  With a modulating burner, how else could you possible do it??



    As a matter of fact, with a lot of messing with controller codes, it IS possible to make ODR / weather compensation and external control co-exist.  But philosophically, I can't understand why you think that the Flow temperature of a boiler, whether it's adjusted by odr or not, has ANYTHING to do with how it's turned on and off!  When I command a boiler on, by whatever means, I expect it to deliver heat at whatever setpoint I determine, either static, or dynamic via Opentherm, 0-10V or whatever.  I  might want a dynamic setpoint, eg. because there are radiators AND underfloor heating in the same building and I want to set the boiler to the lowest acceptable Flow temperature, depending on what's demanding heat at the time.  If the demands all go away, I want the boiler OFF.  Why would odr make it continue to run??  (BTW, the factory setting of the weather comp logic on the Vitotrol 200 controller integrates outside temperature over TWENTY THREE HOURS before using the mean to calculate the odr Flow setpoint.  Just one of the variables you have to mess with to make the thing work 'properly'.



    And ALL the condensing, modulating boilers I work with, including Viessmann, automatically reduce output to match actual BTUs demanded, as measured by Flow / Return delta-T or equivalent.  So a 30kW boiler will happily and automtically turn-down to 6kW and run all day like that, if demand persists.  I therefore cannot understand at all your previous comment ' How else would I be able to move the btu's these boilers can make' and the other information leading up to that.  Any reasonable boiler will automatically adjust its output to match demand - end of!  and suggesting that:



     'External Demand..... Once you utilize external demand you are initiating

    a heating program changeover, blocking circulation pumps and burner and

    creating s minimum boiler water temp setpoint. You have effectively

    taken away the boilers firing logic as it pertains to the boiler

    ability to modulate water temp based on outdoor reset.'



    makes no sense to me at all and fails to correspond with how it works on boilers I deal with here



    And for your further information, most boilers will NOT allow a delta-T as high as 40F (22C degrees).  In fact, I was working yesterday replumbing a system with a Vaillant boiler that was persistently erroring ('S.53' fault) EXACTLY because delta-T exceeded 18C degrees (32F degrees).  It's a well-known problem under certain situations!  And mostly because the response time of the burner modulation software is too slow to throttle back before the Flow gets too hot.  Vaillant can't / won't change the software, so I get to change the plumbing!
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited November 2011
    Facts Checked, Still the Same

    The current WB2B which has been available for 3yrs in the US and 8yrs on your side of the pond uses Lamda Pro Combustion. Air and gas operate independently of each other. I can ramp inducer rpms until the cows come home and have no effect on the amount of gas I give to the burner.



    Concerning flow rate. The max flow rate for a WB2B35 for example is 6.2gpm. How would I be able to move its 114,000 btu output on a 20 degree delta-t? I would have to run a 40 or I wouldn't be able to get what the boiler can give and my boiler pump stays small. In this example a Taco 00R on Speed 2 because my head is 13' at the below flow rate.



    5.7gpm x 40 x 500 = 114,000



    If I take your logic and run a 20 the most btu's I would get out of the boiler is 62,000 and my pump becomes much larger due to the 16' plus of head. I'd be in a Grunfoss UPS26-99 and still not get what the boiler can deliver. Would have some awfully upset homeowners when I couldn't give them heat when they needed it the most.





    Vitodens 200 uses the information from the LLH sensor to tell the boiler to or not to fire. If the temp in the LLH drops below the system requirement the boiler will fire. System requirement comes from the selected heating curve and outdoor temp. I have rarely if ever used the "system pump" plug in the power pump module. We don't run too many constant circulation systems here and these are the best types of systems for Vitotrols in my opinion. As for Vitotrols, I use 300's for the small price cost over the 200 customer has some control of the boiler as well as DHW.



    The boiler calculates water setpoint based on odr or room temp via a Vitotrol and on the slop/shift of the heating curve. When external demand is engage you are programming some type of heating circuit changeover. ie, Snowmelt, pool heat exchanger or any other type of application where you need to maintain a fixed setpoint.



    In codeing 2 address 34 I can influence my pumps and what effect that External Demand signal has on them. In coding 2 address 91 I can effectively choose which heating circuit I want an external heating program changeover. In address 9b I then select my minimum boiler water temp setpoint for that heating program changeover. In coding address d5 you can select which direction you want to go with the external heating program change over to go., constant heating mode, permanently reduced or permanent standby In address F2 I can now select for how long I want that change over to last up to 12 hours.



    My point concerning external demand is that it is mis applied more often then it is applied correctly and is not the means to turn the boiler on and off. Let the LLH sensor do its job and just turn on a system side pump or zone pump.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • croydoncorgi
    croydoncorgi Member Posts: 83
    Turning (positively) Off

    As it happens, pump noise was one of the key problems with the WB2A to which I added external control (from a Hometronic box) and co-existed it with odr/weather comp.  The system pump had originally been a modulating Wilo model but was replaced under warranty by Viessmann when it failed long before I came on the scene.  For reasons I never fully diagnosed, there was a lot of resonance from pump noise coming from under a tiled floor.  It was bad before but (apparently) much worse with the replacement fixed-speed pump (Viessmann UK had a LOT of warranty calls on that pump, so changed them to fixed-speed whenever possible!).



    Anyway, I had to stop the noise as best I could, without digging the floor.  So: external control to switch off the boiler completely when no demand for heating from the Hometronic system.  (It is ALWAYS what I do on smaller systems.  Even on a 120kW system with 2 boilers on a header, just keeping the pipes warm (as this bigger system happens to do) costs a LOT of gas.  In my opinion, on virtually any system, leaving the boiler and primary circulator running 24/7 (which is the result of what you're proposing) will likely use up ALL the efficiency gains from having odr/weather comp in the first place!)
  • CMadatMe
    CMadatMe Member Posts: 3,086
    I think

    That's what you are missing. Here in the US we like to zone everything via valves or pumps. My pump doesn't run 24/7. The only time my boiler pump is going to run is when I need heat. Once I turn on a zone and take temp out of the LLH the boiler will fire if need be using the information from the LLH sensor. We don't use the 20A plug (system pump) output nor do we use variable speed pumps as boiler pumps. I was however thinking about trying a Taco VDT pump as my boiler pump in the Vitodens I'm getting ready to install in my house in the next week or so.



    I did notice in the US manual that coding address E5 (Without variable speed heating circuit pump. Do not adjust) is set to zero and in the UK manual you have loads of adjustments for using variable speed pumps. You also have the newer version Vitotronic control and lower end 4.8kw minimum as well as a 200 Combi. Hoping to see this stuff in 2013 or sooner here.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • croydoncorgi
    croydoncorgi Member Posts: 83
    Lost energy!

    Quote:

    Once I turn on a zone and take temp out of the LLH the boiler will fire if need be using the information from the LLH sensor...



    Exactly!  You've got the boiler re-heating the water in the loop whenever the LLH sensor drops below 'x' degrees and (presumably) a shunt pump continuously driving water round the loop between boiler and LLH (otherwise you couldn't trust the sensor output).  So 24/7 you're burning (a little) gas to keep the pipes and LLH warm and (a little) electricity to turn the pump (and the fan in the boiler, ...).  Given the small amount of energy saved from (eg) odr, why bother with it at all?  The saving will be less than the overheads!
  • SWEI
    SWEI Member Posts: 7,356
    boiler circ speed control

    Boiler circulator speed should really be managed by the onboard boiler controls.  PWM pumps are not as widely available here, so we are pretty much stuck with triacs and inefficient single phase motors here in North America.  None of the smart circ manufacturers currently offer a delta-T mode (I keep asking but they all say it would be too complicated for the installers or that there is no demand for it.)  They don't even offer external inputs as an option for their small circs, which would at least allow us to roll our own.  You can add external input modules to both Magna and Stratos circs, but even the smaller models of those are massively oversized for pretty much anything under about 500 MBTU/h.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Its Coming

    The bumblee is just around the corner.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • SWEI
    SWEI Member Posts: 7,356
    Bumblebee

    Cool!  Time to call my Taco rep.
  • croydoncorgi
    croydoncorgi Member Posts: 83
    How to control a shunt pump

    Quote:

    Boiler circulator speed should really be managed by the onboard boiler controls.



    Yup - definitely agree - in principle.  But in practice, if the boiler only has an On/Off control for the pump, or nothing, you have to do something different.



    I'm interested to hear that someone in the US has also recognized the value of a delta-T controlled pump.  Why not?  With some sort of adjustment provided (to set upper and / or lower limit temperatures and a speed adjuster, it could be used for a number of things, including shunt pumps.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Taco

    Has the VDT pump. Set your delta-t and away you go. Used many of them as sytem pumps and going to try one on my own Vitodens as a boiler pump.



    http://flopro.taco-hvac.com/products/Wet%20Rotor%20Circulators/index.html?category=372
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • croydoncorgi
    croydoncorgi Member Posts: 83
    Output control on Viessmann

    Quote:  Air and gas operate independently of each other. I can ramp inducer

    rpms until the cows come home and have no effect on the amount of gas I

    give to the burner.



    I'm still waiting for the explanation of how Viessmann boilers (WB2B and other current models) control the output of the boiler (ie. the burner rate) if not by changing the fan RPM.  And if the fan RPM is in fact used ('far as I can see, it's the only method available!), how can fan RPM and gas input NOT be related??  OK - I know perfectly well that the latest versions of Viessmann (and I think also the previous 'matrix' burner models) use ionization current to tweak the gas/air ratio.  But the basic gas-train is a 'zero pressure governor' system, with a venturi providing the dynamic pressure drop (according to fan RPM!) which gets the gas out of the valve.  Hence, there IS a rigid link between fan RPM and gas input.



    Please tell me where this interpretation is incorrect.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited November 2011
    Lamda Pro

    They work independently from each other. Took this from the TDM.. Just because my rpms ramp up does not necessarily mean the gas valve flies wide open with it. It looks at the gas quality then the gas valves decides the amount of gas..









    The combustion management system utilizes the physical correlation between the level of the ionization current and the air factor λ. For all gas qualities, the maximum ionization current results with air factor 1. The ionization signal is evaluated by the combustion management system, and the air factor is adjusted to between λ=1.24 and 1.44. This range provides for an optimum combustion quality. Thereafter, the electronic gas valve regulates the required gas volume based on the prevailing gas quality.

    To check the combustion quality, the CO2 content or the O2 content of the flue gas is measured. The actual values enable the prevailing air factor to be determined.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • SWEI
    SWEI Member Posts: 7,356
    Taco VDT pumps

    These pumps have PSC motors and a triac-based speed control.  This is the same technology as a Tekmar 356 or a Heat-Timer DigiSpan VSP Elite.  They get the job done, but not very efficiently.



    So-called smart circulators are built around electronically commutated permanent magnet motors, which typically consume less than half as much energy (and allow much greater turndown ratios.)
  • croydoncorgi
    croydoncorgi Member Posts: 83
    No point reproducing the words frrom the manual!!

    Think about it.

    Virtually any of the high efficiency boilers on the market, including Viessmann, has a 'turn-down' factor which allows, for example, a 30kW boiler to operate with an output of maybe 7 or 8 kW.  To achieve this turn-down, there needs to be a MASSIVE reduction in the flow of gas/air mix through the boiler.  Changes to the gas/air ratio achieved by (manually) adjusting the throttle and/or the offset adjusters on the gas valve/venturi assembly, or in the case of Viessmann's latest products, automatic adjustment using ionization current to indicate flame quality, are NOTHING to do with the kW/BTU output of the boiler. 



    The design logic of ALL the boilers of this type that I'm familiar with is that the gas train delivers a FIXED RATIO of gas/air mixture by use of a venturi.  The faster the fan turns, the more air through the venturi, so more gas out of the zero-pressure gas valve, so more output from the burner.  You may be confused by the fact that on the Viessmann 200 series, the venturi is part of the fan - a clue is in the name of  the  bent plastic pipe that ducts air into the fan - 'venturi extension'.
  • NYplumber
    NYplumber Member Posts: 503
    great discussion

    Picking up interesting information.



    More interested in lambapro talk than pwm at this point....
    :NYplumber:
  • bob_46
    bob_46 Member Posts: 813
    lambda pro

    This technology has bee around a long time on industrial burners. It was developed for

    automotive use in the late 70's by Volvo and Bosch and is on all cars now.



    http://www.youtube.com/watch?v=5B0V07iE5uw
    bob
  • Stratos or Magna Minimuim Boiler Size

    I noticed a statement "even the smaller models of those (Stratos and Magna) are massively over-sized for pretty much anything under about 500 MBTU/h".



    Sorry to say that is not true.  The Stratos 1.25 3 x 20 (our smallest of 10 models) maximum head is delivered from zero to 12 USGPM (up to 120,000 BTU @ 20 deg delta T).  Wattage range is from 9 to 85 watts.



    So (and I hope this does not sound like a sales pitch) it can handle even the smallest boilers.  Just wanted to clarify this...
  • NYplumber
    NYplumber Member Posts: 503
    Unfamiliar w/ viessman

    Does viessman use a mass air or oxygen sensor to calculate the mix as fuel injection cars do?
    :NYplumber:
  • SWEI
    SWEI Member Posts: 7,356
    Stratos sizing

    I should have qualified my comments as pertaining to boiler circs as used in a modern well engineered (high-flow, low head) primary loop.  The Stratos pumps make fantastic system circulators (and the range offers a good fit for the light-medium commercial market.)



    I need to call you this week anyway.
  • croydoncorgi
    croydoncorgi Member Posts: 83
    Ionization current vs mass-air sensor

    Quote: Does viessman use a mass air or oxygen sensor to calculate the mix as fuel injection cars do



    No.  (pending an answer from Chris that negates everything I've said about the way this stuff works (or works differently in the case of Viessmann!  (But I'm not holding my breath.))



    The boiler's internal controller software has a 'map' that correlates fan RPM with a given rate of temperature rise at given output BTUs, so it looks at its sensors (Flow, Return in most, but in the case of Viessmann, Flow and exhaust temperature) and then increases or decreases fan RPM to deliver more/less gas+air to the burner and therefore more/less output according to whether Flow temp is rising/falling, how close it is to the current setpoint and also whether the delta-T Flow/Return is at the limit.



    Since it knows pretty-much exactly the performance parameters of the fan (x volume at y RPM) it doesn't need to measure the gas/air volume.  In fact, it doesn't even need to know the volume.  The gas train delivers the right mix automatically: the zero-pressure governor mechanics plus the venturi takes care of the gas/air ratio, so the boiler delivers the desired output with the burner conditions self-regulated all the time.  The controller only needs to turn the fan RPM up and down between the set minimum and maximum.



    The electronic connection to the zero-pressure valve, to adjust the gas/air ratio is completely separate from the system that controls the boiler output.  The zero-pressure valve will deliver the same ratio of gas and air across a wide range of flow-rates.  The ionization current measured across the burner flame is primarily there to prove that it's lit but also has the useful additional property of varying according to the flame characteristics, which change with gas quality. (see Viessmann text above quoted by Chris).  I suggest the statement in that:



    'Thereafter, the electronic gas valve regulates the required gas volume based on the prevailing gas quality.'



    is slightly misleading.  The electronics tweaks the valve settings now and then to optimise the gas/air ratio, and the valve mechanics then deliver that ratio across the whole output range.  I stand to be corrected on the detail - but I don't think there's a 'servo loop' as such between ioniztion probe output and the gas valve: the electronics tests the current at intervals and only tweaks the valve if the current changes.  The current will stay the same unless the gas quality changes.  I believe  the controller ramps up to full power for a few seconds to do the check.
  • NYplumber
    NYplumber Member Posts: 503
    Thanks!

    thanks for the explanation. I see how it differs from the "other" modcons.



    Is this design logic limited to the 200 & 300 series or included in the 100's too?
    :NYplumber:
  • croydoncorgi
    croydoncorgi Member Posts: 83
    Vitodens 100 is different

    Quote:

    Is this design logic limited to the 200 & 300 series or included in the 100's too?



    The 100 models in UK are different from the 200s (300s mostly no longer brought into UK!!).  They have the same type of zero-pressure valve setup but the adjustment on it is manual only.  No link to use the burner ionization current to tweak the gas valve settings automatically.



    But be careful with direct comparisons between models that sound the same but may be different (slightly or a lot!) in different countries.
This discussion has been closed.