Heating Help

Horses for Course

@ January 7, 2012 2:19 PM in Electric versus propane and oil.

IC engines used as 'micro-CHP' power sources can be remarkably efficient.
Danish company I'm familiar with has a system with  Toyota-origin gas-engine (runs on methane or LPG) and delivers about 35kW of heat (via the cooling system) and 14kW of electricity.

To make best use of such a machine, you need a bottomless 'heat-dump' for the heat output.  Then, the Run/Not Run decision is based on the price you can get for the electrical output, assuming you're going to sell it back to your grid supplier, or whether it will be cheaper to use the CHP electricity than grid-supply.  There are of course more complex calculations based on the total cost of running the machine versus the combined value of the heat and electricity produced, versus the cost of electricity and heat from other sources.  The controller on the machine does these calcs in real-time and starts and stops it automatically.

Note also a well-designed CHP machine can run for 100000+ hours between major services (!!)

LEED is the answer!

@ January 4, 2012 8:28 PM in Electric versus propane and oil.

The ground source heat pump system at my sister's house (at 5500 feet in Utah) gives energy performance 25% of US average domestic energy consumption! LEED Platinum, second in Utah!

Pump kick

@ January 3, 2012 2:42 PM in Pump to or From modcon

Further reasons why pumps go on the Return side:

- some furnaces need  a pressure 'kick' when the pump starts to confirm the pump is running.  Pump is powered from the furnace and the kick is needed during each ignition sequence,

- Some furnaces have auto air vents between the Return and the HX, or on the HX itself.  If you have the pump on the Flow side, there's a possibility that air gets drawn into the AAV if/when system static pressure is accidentally gets too low.  Bad Thing!

Suitable hat?

@ January 2, 2012 10:33 AM in New service vehicle

...with arrows in it?

And you'll be all set to go!  :=)

Useful hint?

@ January 2, 2012 10:31 AM in Over Pumping Solution, 2nd Try

Why not type up your complete message in (eg) Windows Notepad and then copy it into the Heating Help entry form??

Do what they do / say

@ January 1, 2012 7:49 PM in Pump to or From modcon

....bearing in mind that 'system' boilers (from Viessmann etc. ie. those with a pump built-in)  ALL have pumps on the Return side.

Va!luable people - both sides of the Ditch

@ December 29, 2011 5:12 PM in Review by "experts"

You're totally right!
People like Tim are valuable - but unvalued everywhere!

Depressing thought how time is taking its toll with no reliable source of replacements.

Stat drives pump!

@ December 27, 2011 8:45 PM in Grundfos Alpha "fighting" a Honeywell SmartResponse?

What no-one has yet pointed out (?? - not sure I fully understand the setup...) is that the stat in the original question will be driving the electrical circuit that includes the pump, so they can't 'fight'.  Until the stat calls for heat, the pump will / should be off.  The auto-adapt (or whatever mode you select) will only apply once it's powered.

The other issue (getting the temperatures for the furnace and the various demands correct and compatible) sounds like more design work is needed!

...I also lack any experience of the Garn machine - but I get edgy when people discuss  connecting an 'uncontrollable' heat source such as a wood burner to anything including valves or thermostats.  Point being that some wood burners will overheat and boil in no-flow situations.  Garn seems not to do this, since it's said to have enough water volume in its own tank to keep from boiling in every situation(??).  Design seems to require 'batch firing' - each wood charge has to burn through completely before any refilling of the combustion chamber.

'Knowing the science '

@ December 27, 2011 8:33 PM in Review by "experts"

is the LEAST likely scenario.

Most of the problems gas fitters both sides of the pond have with exams are from two causes:
- not understanding the science in the first place
- not being prepared to listen and learn, sometimes based on 'Sonny, I was doing this job before you were conceived...'

These, and being blind-sided by the thought of any exam!  Quite surprising the number of people who get mental paralysis at even the thought of being tested at anything.

Thanks

@ December 22, 2011 2:26 PM in One for the (really) Old Timers!

Good to hear from you, Timmy..
Hope all goes well in RI

REAL Roberts Gordon thru & thru

@ December 21, 2011 9:28 PM in One for the (really) Old Timers!

The data plate is mounted on the casing of the furnace (inside) and is definitely showing the company name, the type (as above) and a serial number (starting 65, which might be a bit of a clue!).

The burner system is an unusual design, consisting of an injector, a horizontal mixing tube / venturi, a right-angle bend upwards and a round burner, with the pilot assembly beside it.  Definitely could not be separated from the rest of the machine.

Room optimization, not ODR

@ December 21, 2011 4:12 PM in The brains of Apple have made there way to HVAC

Far as I know, the nest uses an optimization algorithm based on rate of temperature change in the room to calculate On and Off timings.

And it is strictly an On/Off device - no direct control of burner modulation and/or Flow temperature.

Jewellery versus functionality!

@ December 21, 2011 3:51 PM in The brains of Apple have made there way to HVAC

Apple very cleverly added style to substance with their IPad / IPhone / Ipod products.  The Nest product spun out of Apple is doing the same thing - making a thermostat sexy!  But although sex sells, I'm not convinced that a mass-market thermostat can be sold at $250!  But then - I'd never have forecast massive sales at the original Ipod price-point until they happened.....

One for the (really) Old Timers!

@ December 21, 2011 3:22 PM in One for the (really) Old Timers!

Visiting relatives near Toronto, I find they have an incredibly old warm-air furnace in their recently-purchased house.  It has obviously had additions over the years (a humidifier and an A/C coil in the Return air duct, at least, plus possibly a non-standard gas valve).

However, it seems to still be working - maybe as well as it ever did!  All it definitely needed was a new fan drive belt.  In general, it looks fine.  The Home Inspector reported it as 'about 25 years old' but OK.

Furnace is a Roberts Gordon GL100-A.  Gas valve is White Rogers 36C03.  As far as I can discover, Roberts Gordon stopped making this model in 1969!

Anyone remember anything about this furnace? 

I'm thinking maybe at least a smoke test of the heat-exchanger would be good idea.  But of course I'm from UK and like a fish out of water in Canada.  Where would I get a smoke cartridge in Hamilton, Ontario!!??

Why 4-way mixer

@ December 19, 2011 7:14 PM in Mandated reset controls in 2012

In my limited experience of where these have been used in a high-efficiency system, they've been a big problem!  The issue is that you definitely do not want to recycle hot water from the Flow straight back to the boiler (which is what a 4-way valve usually does...).  If any blending function is needed, better use a 3-way blending valve.  Ideally, adjust the temperature of the whole system down, starting with the furnace. 
Then you've got some hope of keeping the Return temperature low enough to allow condensing to occur.

Be careful! Condensation causes corrosion

@ December 13, 2011 6:22 PM in Lowering water temps on Viessmann vitogas

As far as I can see (Vitogas models don't come to the UK market) this is a cast-iron boiler which should NOT be allowed to condense.  In other words, the flue gas temperature needs to stay above 135F or so.  Return temperature must be kept high enough to ensure this is maintained.  If your FLOW temperature is as low as 133, you're at serious risk of wrecking the heat-exchanger

Essential for H/E gas boilers

@ December 3, 2011 11:37 AM in combustion analysis

A CA / Flue Gas Analyzer is essential for the great majority of existing high-efficiency gas burners (except the very few with automatic adjustment - and even those shoud be double checked with a separate instrument).

If you don't get the gas / air mix spot-on, efficiency will go down and / or boiler life will be shortened due to excessive solid combustion products, hot-spots etc.

And often a combustion quality check is a valid alternative to stripping down the burner assembly on most machines much of the time.  If it ain't broke don't fix it.  With reasonable gas quality and the burner set up right, a burner should be able to go 2 or even 3 years with no need for cleaning.

Reading here about (eg.) Viessmann heat exchangers needing frequent cleaning with heavy duty chemicals sounds worrying.  Are they in fact set up right?  Or is piped gas in the US full of sulfur or whatever?

If in doubt - ask....

@ November 30, 2011 3:55 PM in Pump speed control - How do you guys do it?

Gordan summarises neatly what I've been saying about how the Viessmann burner system works.

I called Viessmann technical department  in UK today:
- yes - it's a zero-pressure regulator,
- no - the burner controller does NOT adjust the gas mix all the time according to ionization current.  The tech thought it only happened on burner start.  And for the measurement to work, the burner needs to be on full power for a while.
- and perhaps most important, it is fan RPM (only) that regulates the burner output.

The video is correct but it never says HOW OFTEN the process takes place.   It only shows the part of the gas valve that is adjusted by the Lamda system.  The effect of that adjustment is to change the 'zero-pressure' and therefore the gas/air ratio.  The new setting will then last until it's changed again.

And in the real world, how often does gas quality actually change?   Not often - so no need to tweak the mix frquently / continuouosly.

We'll have to totally disagree on this

@ November 28, 2011 8:54 PM in Pump speed control - How do you guys do it?

Quote: Air does its own thing and gas does its own thing. They work independent. The gas valve operates off the Ionisation current feed by the Ionisation electrode.. If i'm burning rich gas valve backs off not fan speed until I get back to Lamda of 1,3. If I'm burning lean gas valve opens until I get back to Lamda 1,3. fan speed does not increase nor decrease.Unless you work for Viessmann AND have been on training courses (in Germany?) that gave you this information directly, I'm prepared to state that your description of what happens is wrong.For a start,  my Viessmann documentation says that the ionization-current-based adjustment of the gas valve can only happen with the boiler at full power, and it actually throttles-up for 5 seconds or so, periodically, to check the adjustment.  As I said, the whole principle of the gas train is that the venturi / zero-pressure valve combination gives a more-or-less constant gas/air ratio across the full power range.  So all that needs to happen to make the thing throttle-up is to increase the fan RPM.  Adjustments to the gas-valve using the ionisation current input happen only every few hours, I believe.  But the controller automatically adjusts the power output continuously, every few seconds, and only via changes to the fan RPM.

It's simplicity versus complexity = cost

@ November 28, 2011 1:34 PM in Navien "Mod-Con" Turn down

The reason (AFAIK) that the turndown ratio on zero-pressure gas trains maxes-out at about 4 or maybe 5 is to do with venturi design.  It's relatively easy to make a venturi where the pressure drop is roughly linear over the sort of flow rate range that 4:1 turndown implies.  But if you go further than that, the gas/air ratio will start to drift away from the desired point at one or both ends of the scale.

Most boilers I work with have 2 adjusters:
- throttle, which adjusts the 'aperture' of the pipe feeding gas to the venturi,
- and an 'offset' screw on the body of the gas valve.

Most boilers have a setup procedure which starts with getting the boiler at full power and then adjusting the throttle to give the correct CO2 or O2 percent as measured by a gas analyzer probe in the flue.  Once that's set right, then you reduce the output to minimum and adjust the ofset screw to the same or very similar value.  Then you put it back of full power and recheck the value and if necessary, readjust the throttle.  And so on ad nauseam until both the full and minimum power numbers are correct.  In practice, I've only ever had to go through the process at most twice.  Normally, unless the adjustment is completely screwed up, it's only one adjustment at each power setting.

The worst case scenario is when the settings have been so badly messed up that the thing won't light, or lights with such a rich mix that the CO level kills the gas analyzer.  Then you have to whip the probe smartly out of the flue before the sensors are permanently damaged and adjust the valve by 'counting turns' of the throttle and / or looking at the flame picture and twiddling the throttle until it stops being bright yellow!  :=)

Fortunately, most burners fire up at a reasonable level and stay lit at full power even if well off the correct setting.  It's at the low power setting that the burner goes out randomly!

Vitodens 100 is different

@ November 28, 2011 1:13 PM in Pump speed control - How do you guys do it?

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.

Horses for Courses

@ November 28, 2011 6:01 AM in Navien "Mod-Con" Turn down

From what I know about combustion technologies, I believe Viessmann, etc. are at the limit for turn-down ration at about 4:1 using the 'industry standard'  zero-pressure governor (don't know if this is the terminology used in N America).

Other manufacturers such as Rinnai, that need to achieve a higher ratio, have to do it with different technology.  Rinnai water heaters achieve (I believe) 16:1 ratio using a multi-stage valve with a stepper motor in it (I know it's a stepper - I can sometimes hear mine gowling and chattering on the outside wall of my house as it adjusts the burner rate to the water flow.  Brilliant system for its purpose.

But I question why you might need a bigger turn-down ratio for a combi boiler.  Millions of these are sold in Europe, especially UK.  Unless they're over-sized for the job, 4:1 seems fine to me - not much problem with the boiler cycling on an off at very low heat demands, in practice.

(Being an ignorant ex-colonialist / imperialist here in UK, I know nothing about the content of ASME H standard / certification in N America!  What areas of 'heating equipment' does it cover?  To avoid contaminating this thread, maybe someone prepared to provide a brief overview will start a new thread.   Thanks.)