How much ciculation is needed in loop with retrofit boiler

Perry_2

Yesturday and today I had several discussions with regional level distributors on the Vitoden 200, my application, and my concerns (as discussed in various post above).

Todays conversation was with a person considered to be very knowlegable on the controls.

It was acknowledged that in this type of retrofit - without TRVs to control room temperature - that the Vitoden 200 could indeed overheat or insufficiently heat a house based on only outdoor temperature curves due to non temperature based weather issues.

It was acknowledged that if I hooked the secondary loop circulating pump to a thermostate - that the boiler would indeed needlessly cycle as it maintained Low Loss Header temperature in absence of any demand for house heating in the spring and fall. This mode of operation would also limit the ability for the Vitoden 200 to learn your house and modify its operation to maximize long term boiler efficiency.

The answer in my application: retrofit of not quite 100 ft Cast Iron bassboard with Monoflo T loop system is to use the Remote Control "RS" as it provides actual house temperature feedback to the Vitoden 200 (in part acting like a house thermostat - but it is does more than that in that it communicates other settings to the Vitoden 200). Based on the settings and the feedback from the RS remote control the Vitoden 200 can modify loop temperature, setback curve, and boiler operation in order to optimize house heating and efficiency.

This will work in my application because there is only about 25 gallons of water in my heating circuit - which does not make it a large water content system. There is about 15 gallons of water in the baseboard. 6.3 galons of water in the 80 ft of 1 1/4 pipe, and about 3.7 gallons in an estimated 220 ft of 1/2" pipe.

This is not considered a high water volumn system such as underfloor heating with its usual many thousands of feet of tubing; and support piping for that tubing.

Thus, retrofits of Cast Iron Baseboard systems, without TRVs, can be adequtely controlled using the "RS" remote control to provide house temperature feedback.

The secondary circulating pump will be controlled by the expansion board in the power supply through the Vitoden 200. Essentially, this is just an on / off control. The Vitoden 200 will start itself and the secondary circulating pump when there is a call for heat in the house, and shut the pump (and itself) off when there is no longer a need to be heating the house.

I hope this helps everyone understand how to do a good retrofit of a Cast Iron Baseboard Monoflo system with the Vitoden 200.

Now if they only had a 4.5-18 boiler model...

Perry

Perry_2

How much circulation is needed when retrofitting boilers

I would like to thank everyone with the help on the value of the condensing boiler thread.

Here is another question - will my existing system work with a new condensing boiler which circulates a lot less water (on a GPM basis).

I ask becasue the condensing boilers I have looked at seem to have fairly low capacity pumps. Specifically the Vitodens 200 has a pump that maxes out at about 6 GPM.

My existing system has a Bell & Gossett Series 100 pump which deadheads at 8 Ft head, maxes out at about 35 GPM - and assuming that it is running in the good range of the curve may well be pumping 15 to 20 GPM.

Under the previous thread it was identified that my real heat load is probably in the range of 30 - 40,000 BTU/Hr.

So would my existing system operate properly with a reduced flow? Or, will an additional circulating pump be needed in the system (or other things).

I know that many of you can calculate things in your head (or easily) that I would struggle with (or don't even know how).

The existing system is a 52 year young Crane-Line firetube boiler (round) 132,000 BTU/Hr.

Normal 1-1/4 single pipe system with monoflo tee's; 140 F system; 99 Ft of cast iron baseboard. 10 baseboard assemblies (6 1st floor & 4 2nd foor).

Aprox 80 Ft of 1-1/4 pipe, 4) 90 Deg elbows in system, 7) 90 deg elbows (or equivalent) for boiler & circulator connection, 10 monoflow Tee's, 10 supply Tees, and lots of what looks like 1/2" pipe to the radiators with various fittings.

Someone should be able to provide an approximate head loss due to resistance of that system.

So what happens if you start ciruclating 6 GPM (or another low number) in a system like this? Or - will it need another pump and how would you connect it.

Now let me sit back and learn...

Perry

Brad White_9

The Vitodens

has a fairly low residual head available for your use, Perry.

The good side is that your 1-1/4" pipe at 6 GPM or so (plenty for your presumed 40K or so heat loss) is about half to 2/3 of what a pipe that size might usually carry. The number of fittings is of concern even without calculating.

Here is what I would do: Buy the Viessmann Low Loss Header and insulation package. Run your system side to suit your needs and leave a tapping or two for future radiant, heat the basement, what-have-you.

When in doubt about flow or head, the LLH is your friend. That is what I am putting in for a house with CI rads (47 MBH heat loss here in Boston), Same Vitodens and future radiant.

Mike T., Swampeast MO

To use only the built-in circulator, you'll have to completely reverse-engineer the system. Head loss as it progresses through the loop, output of the iron b/b (at temperature based on actual heat load and corresponding supply curve), temperature drop across each element, temperature drop through the loop as a whole, etc.

May or may not be doable, but my gut tells me that there would be balance problems as the loop itself is almost certainly designed around MUCH higher flow rates--particularly if the B&G 100 is the original.

In all likelihood, you'll need the low-loss header. I would however replace the B&G 100 with the Grundfoss 3-speed "Super Brute" or similar. Begin with the lowest possible speed and increase only if you experience balance problems after the system has stabilized for at least 2 days with no thermostat setback.

If you use daily setback, I highly suggest that you first optimize the reset curve--essentially you set the wall thermostat higher than you want and adjust the curve to give the closest to your desired setting--and then set back via the timer in the Vitodens--NOT the thermostat.

Perry_2

At least the pump casing is original

Thanks for the advice. I suspected as much once I saw the pump curve for the Series 100 and compared it to several of the smaller condensing boilers - which is why I asked.

As far as my Series 100 pump. The original casing is still installed. The motor, seal, and I immagine impeller were replaced in 1991 (or at least the replacement that was installed was Mfr in June 1991).

What the future pump will be... We will see. I will remember (print out) your advice on how to set-up and ballance the system - and hope the plumbing contractor knows the same.

Brad White_108

I second the Grundfos

3 Speed Super Brute (with IFC integral flow check) and follow Mike's suggestion regarding speed control, curve setting, anything Vito.

Start with the Grundfos on low and you will be surprised. Remember that by decoupling the boiler circuit from the heating circuit via the LLH, you can devote all of the pump head to your radiators and piping. Near boiler pipe losses and the boiler itself are already absorbed by the internal circulator.

Mike T. is the guru of Vitodens adaption to existing CI systems. Trust me on this and I am not the only one who has noticed.

Ragu_5

Hey Mike and Brad

I think you BOTH are pretty smart fellers and I've learned a lot from both of you. Low Loss Headers sure seem to make a lot of sense in these applications. Please keep up the good work!

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Perry_2

Will I need extra controls to run the Grundfoss loop pump?

How would the controls be set-up and will I need something special for the Grundfoss loop pump?

Does the Vitodens 200 controler have the capability to control the loop pump as well as the built in boiler pump?

Keep in mind I am looking to have outdoor temperature setback for the boiler water temperature. Also daily house temp setback for work and sleeping hours (once things are set-up).

So how would the controls be set-up?

Currently, the Series 100 pump is controlled by my house thermostat; and the boiler fires based on boiler temperature (allowing the circulator pump to run a lot when the boiler is not firing).

Perry

Brad White_9

Vitodens Pump Outputs

I got two different answers to the same question and am sorting that one out myself.

Bottom line (and how I will be handling my own system until such time as I expand it to serve radiant zones in the future) is to run the radiation circulator independently.

By this I will either manually switch it or use a Ranco controller responding to outside temperature. (Below 65F the radiation circulator runs. Simple.)

The only thing one would miss is warm weather shut-down but with the Ranco, that is done.

Brendan_2

LLH

Brad or Mike:

What advantage has the LLH over simple primary/secondary pipeing, isn't decoupling achieved in both? just wondering
Thanks
Brendan

Brad White_9

Low Loss Header

Fair question. Yes, both will hydraulically decouple the two systems.

The reasons I chose the LLH over what I could make myself:

1) My secondary (system side) circulation flow rate will eventually be much larger than my initial setup. (I have a 3-port outlet header, one for the current radiators, two for future radiant zones.)

For me to do that with pipe and fittings would mean a series of headers or a parallel P/S setup to fit in all of the branches for equal starting temperatures. A lot of joints to check and torque or solder. LLH? Four flow connectons. Done.

2) The control sensor well is built in and designed to work with the Vitodens and the sensor comes with it. Sure, I could put in a well and sensor in my piping, but would the Vitodens care? I have an engineered system.

3) The "wide spot in the road" feature give an opportunity for loose particulates (despite my best cleaning) to fall out of solution to be drained away. Also allows venting and purging of the boiler and system circuits independently with proper isolation. Comes in handy when I am starting up, or cleaning one side while installing the other.

4) With the insulated jacket it looks really neat.

Overall, could I make such a device or function happen with pipe and fittings? Sure. But my time is better spent elsewhere.

My $0.02

Brad

Mike T., Swampeast MO

LLH is All About Return Temperature

See attached diagram.

The LLH header ensures that the water temperature returning from the emitters is identical to the return leading to the boiler. Notice how flow directions are logical.

Compare to diagram of primary-secondary. See how water has to move "backwards" between the tees with both of the tees working in "bullhead" fashion? I know it's supposed to work just fine this way and that return temp to the boiler isn't supposed to be elevated and the primary (boiler) flow is not supposed to be in any way affected, but it just doesn't seem as logical, straight-forward and foolproof as the LLH.

Viessmann only recommendeds the use of a LLH when hydraulic decoupling is required--NOT primary-secondary. Also notice the sensor location in the LLH. Probably difficult if not impossible to find such a "sweet spot" for measuring the "sort of mixed" temperature if you use primary/secondary. I suspect the boiler takes advantage of that position to better ensure that the remaining operational parameters shown in the LLH illustration are always true. The LLH also forms a natural "debris trap".

Do however imagine what happens when secondary (emitter) flow greatly exceeds primary (boiler) flow. Delta-t through the secondary will decrease as flow increases--thus more and more return water mixes into the supply stream. The internal temperature of the boiler will have to increase to maintain target at the LLH sensor location. This will somewhat reduce efficiency compared to a situation where secondary flow is closer to that of the primary. This is why I suggested the "Super Brute" or similar and to first try the lowest possible speed.

Brad White_9

Much better stated, Mike-

In point of fact, at Viessmann Warwick last week, their tall LLH had illustrated the equal system and boiler return temperatures. Thanks for making that point so clear.

Mike T., Swampeast MO

Ready Perry?

You asked a wonderful question and gave great information.

Here's a reasonable scenario.

Let's say the house requires 25,000 btu/hr to maintain your indoor setpoint. Depending on your estimate of "real heat load" and climate that would vary from about "typical" weather to quite cold.

Assuming Burnham Baseray or similar and interpolating from output charts, that means you need about 127°F average temperature for the baseboard.

Let's say you keep the B&G 100 and use the low-loss header. 20 gpm is a reasonable flow estimate. At 20 gpm with 25,000 btu, temperature drop (delta-t) is a mere 2.5°F!

This means you need 128.25° supply to the system with 125.75° return.

So, the Vitodens MUST work with 125.75° return as it will be exactly equal to the return from the radiation.

Now, refer back to the diagram of the low-loss header and remember that all secondary (emitter) flow that exceeds primary (boiler) flow MUST blend back into the supply to the radiation.

The blended flow formula:

(Temp A * gpm) + (Temp B * gpm) = (Temp C * gpm)

This is not the regression, but where x = boiler supply temperature:

(17 * 125.75°) + (3 * x) = (20 * 128.5°)

x = 144° supply temperature from the boiler.

To reasonably verify:

3 gpm flow @ 25,000 btu = 17° delta-t

17° (boiler delta-t) + 126° (boiler return) = 143° (boiler supply).

So...

Boiler supply about 143°, boiler return about 126° with a required system supply temp of only 128°!!!

See how much the boiler temperature MUST rise when the secondary flow so greatly exceeds primary flow?

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Now let's increase the secondary (emitter) delta-t TEN TIMES to a STILL REASONABLE 25°. Still same load assumed at least average and more likely significantly above average.

Flow requirement PLUMMETS to 2 gpm. Boiler supply temperature reduces 3° to 140 and boiler return drops 11° to 115°. I absolutely guarantee that such will result in significantly increased system efficiency!!!

----------------------------------------------------------

With your diverter tee system I SERIOUSLY doubt that you would have even reasonable balance at such low flow rates unless you add TRVs at considerable expense due to greatly increased labor. Again, this is why I suggested the multi-speed circulator running at the LOWEST possible speed to maintain reasonable balance.

-----------------------------------------------------------

With a 2-pipe system using radiators of any form, new or old, TRVs are an absolute no-brainer addition!!!!!!!!!!!!!!






T

Perry_2

Thanks Mike - the reason I gave such good info is...

Thanks Mike:

What I will do is build a spreadsheet sometime (not today) and play with the various factors to see what happens with a variety of different heat loads. Maybee I'll even build some charts that I can post as well.

The reason I gave such detailed information is that I know such detail would be needed for someone with the knowledge to calculate real answers. Theoretically, as an engineer I know how to calculate lots of things... More realistically I remember how to look things up in books and find the right equations; and none of those books would provide such information as the resistance of a Monofow tee. Besides, in many cases theoretical calculations don't always work out in the real world (largly because the person calculating forgot something).

TRV's are not planned due to radiator design and the radiators and way their ends covers are trimmed. I don't think it would look that good - and think I can get the system to work without them. You are right about the labor involved as well. Not much room to work in.

Perry

Perry_2

A missing link between the coupled systems: Mike & Brad

Let me describe how I think you folks are telling me it should work - then let me tell you about the missing link that I see.

OK Vitodens 200 6-24 connected to the Low Loss Header (primary system); with outdoor temperature setback curve. Secondary side Circulator pump (existing or new) connected to existing Monoflo Tee loop system.

House thermostat connected to secondary circulator pump (as is typical of the older monoflow T systems).

During fall, spring, and warm days in winter - when heat needs are low or very sproatic:

1) House thermostat calls for heat, and starts secondary
circulator pump. Cool water hitting temperature sensor
in LLH starts boiler to warm up water exiting LLH to
match outdoor temp curve.

2) House warms up - and thermostat stops circulating pump.

3) Vitodens controler senses that water in LLH is heating
up and shuts down boiler (and boiler circulator).

4) Heat loss in LLH cools off water. Vitodens controler
senses low temp point and starts boiler and sets boiler
temp as per curve. Boiler circulator pumps circulates
some water through house radiators heating house - even
when not called (and maybee when not needed due to warm
day). House warms up some... (even if only a little).

5) Vitodens controler senses that water in LLH is has
reached high setpoint and shuts down boiler(and boiler
circulator).

6) Heat loss in LLH cools off water. Vitodens controler
senses low temp point and starts boiler and sets boiler
temp as per curve. Boiler circulator pumps circulates
some water through house radiators heating house - even
when not called (and maybee when not needed due to warm
day). House warms up some... (even if only a little).

7) Vitodens controler senses that water in LLH is has
reached high setpoint and shuts down boiler(and boiler
circulator).

Opps - we're in a unneccessary cycling mode due only to insulation losses. How often or long does this go on before heat is again called for in the house by the thermostat? Also of course - you would probably be in this cycle mode prior to my step 1. I also note that there are times that the heat only runs a couple times in a day - and then the whole system cools off.

What is needed is a permissive from the house thermostat. When the thermostat calls to heat the house - it needs to turn on the circulator - and the "heat house" boiler function.

I suspect this will greatly lengthen the life of the boiler.

Of course, the Domestic Hot Water could start the boiler at any time as needed - just like in the summer (or interupt house heating as needed).

Brad, Mike, or anyone: Does the Vitodens 200 allow such an input? Or can you think of any other way to acomplish this.

Perry

Brad White_109

Missing Link

Let me take a stab at this, briefly.

Your first premise is one of a room thermostat controlling the radiation circulator. I favor continuous circulation with or without TRV's.

(Yes I prefer TRV's as does Mike. You can put them in-line below the floor you know, with remote heads).

With continuous circulation the boiler merely fires to maintain space temperature, albeit indirectly via indexed temperature curve.

Without a room sensor (and there is one available as an option but let us assume none), the reset curve rules. The nearly linear relationships between ODT, IDT, HWS and radiator output work in harmony.

The continuous circulation bathes the sensor in water temperature constantly so the transition to change is smooth. With circulator by thermostat control you will see spikes. Your room temperature and the emissivity of the radiators gets a blip with every cycle.

Mike has lived with his Vitodens for a couple of years now; my relationship with the Vito is about to begin, so I will defer to Mike in this regard.

The DHW sequence if I gather your question correctly is just as you describe. The input to the heating circuit is shifted and boosted to limit to heat DHW as ASAP.

One minor point to which I did not get an answer at the Vitodens seminar last week is, why does the output signal to the radiation circulator cease when in DHW mode? This is what they told me, when the Vitodens takes control of external heating circuit circulators.

Why could the radiation circulator not continue to run and dissipate the heat while DHW is being made? So, my tack is to control the radiation circulator independently or at least constantly regardless of my girls hitting the showers.

Mike T., Swampeast MO

Not sure that I understand your "missing link".

By default the Vitodens 200 switches between space heating and DHW--it does not supply both simultaneously. During DHW mode the boiler "wants" to operate at or near full output for the duration of the DHW call. This reduces the time that it's not supplying space heating, but does require extremely efficient heat transfer from the boiler to the DHW tank.

----------------------------------------------

I know this is difficult to understand without actually seeing and measuring, but your sequence of operation is contrary the the overall design of the Vitodens.

Again, look at the LLH illustration. Note that the FINAL goal is ENERGY IN = ENERGY OUT. The boiler will vary the circulator speed to achieve this if at all possible.

Now remember that the Vitodens has neither thermostat connections nor a room temperature sensor but it does have a room temperature setting...

The ENTIRE system is based on ENERGY IN = ENERGY OUT. Do you best to forget that a wall thermostat exists!

Mike T., Swampeast MO

All I can say is to base your calculations on space temperature maintenance.

Once you've done that make your best guess as to the additional energy required to increase space temperature over a given period of time (VERY difficult by the way) and only compounded by the problem that ALL standardized heat loss calculations produce numbers that GREATLY exceed heat required to maintain space temperature. 30% - 50% excess and weighted towards the greater...

Perry_2

Not sure I want the circulator running when the system is cold

Currently I keep the boiler hot 9 months of the year - and turn it off (pilot included) the other 3 months.

During the first two months in the fall - and the last two in the spring I can go days without needing heat, or only need it a bit at night.

So assuming I get the reset curve right. Why would I want the circulator to run all the time when for months in a year what it would mostly be doing is pushing house temperature cold water arround the system? I also note that the literatur indicates that the lowest temperature the Vicodens controls to is 68 F. That's a bit warm for me (especially at night for sleeping). Why would I want to heat the house to a minimum of 68 all the time?

There has to be a way that the Vitodens can control an secondary pump. Don't they have an accessory input (output) for that? Didn't I see a reference to an accessory control card for controling another pump. I'll have to look up more stuff another time.

Perry

Perry_2

Not sure you understand my concern

Mike: This has nothing to do with the theory of operation of the LLH; and I fully understand how the DHW sequence works.

But, what I described is how it would work given the equipment connections I described. This kind of thinking is part of what I get paid for (and my trouble shooting record on understanding system interactions if really good).

I agree with you that the operation I described is contraraty to the intent of the design. That is what makes me think that there has to be a way for the Vitodens to control the secondary pump. Like turning it on and off when the house thermostat calls for heat. I do note that they advertise such a thermostat, complete with daily house temp setbacks.

As I indicated in my message above to Brad; I've got more research to do. I'd hate to think that I would have to find another control system to automate what needs to be done.

Perry

Brad White_109

Expansion Card

There is an expansion card available to do just that, run an external circulator (and for that matter up to two mizing valves if desired).

I am not suggesting you run the circulator 24/7/365. Rather, run it off of an OD sensor such as a Ranco. Circulator runs only when it is 65F or below. No one is suggesting that you circulate cold water all the time.

Constant circulation based on ODT makes things much smoother. TRV's, if you can install them, smooth out what is already a smooth road.

The only "downside" is that some Warm Weather Shut Down (WWSD) programs "exercise" the circulator for a few minutes a week to prevent seizing.

And no, you do not keep the house at temperature all the time (although with radiant floors it is a good thing to do). "Setback" is done by using a downward "parallel shift" in the heating curve off-hours. I have done that for years with my Centra control system dating from 1986. Worked great.

Perry_2

That makes more sense - other heating issues

Brad:

That makes more sense. The Vitodens controls when the secondary ciculation pump runs. If there is no demand for heat in the house; then there is no need to run the pump or the heating boiler.

Note that I am distrustfull of running it based just on the outdoor temperature due to other things that affect how hot (or cold) it gets in the house and the needed heat load.

Things such as:

A) Is it sunny or cloudy? My front windows are targeted to let in UV during the winter for the heat gain - and I have a nice tree to limit it during the summer (and I could plant another nice tree to block the rest).

How windy is it? While I have greatly reduced air leakage, and will be getting more of that; the house will never be sealed like a modern house. In fact, their is not intention to get "all" the air inleakage as I don't need to create "sick building syndrom" or see no need to get to the point that I have to install air exchangers to properly vent the house.

C) Are the bricks warm or cold? While there is some insulation in my walls; it is not enough to insulate the inside of the house from the temperature and thermal mass of the bricks.

D) What is the outdoor humidity (and this relates to more than just a drizzly day. I live very close to Lake Michagan - in what we call the "lake affected zone". The result is that the weather is affected by the temperature and conditions on the lake. This is a benifit during parts of the summer and early winter, and a negative during late winter and parts of spring. 5 miles away from here and they only occasionally see the lake affect. 10 miles away and they never see it.

E) Am I cooking? Sometimes I spend most of a day cooking and put a lot of heat into the house. Filling the freezer with home cooked soups, stews, etc never hurts.

F) Do I have guest that "need" a warmer house temperature than I normally have (I tend to keep things cool as I am more comfortable in cool rooms).

Becasue of the above factors - just controlling things based on outdoor temperature would provide uneaven indore temperatures and comfort.

I will try and get the logic diagrams (or description) of how the expansion card actually interfaces with the secondary circulating pump.

I see the outdoor temperature setback curve as only defining what temperature will be used to heat the house when heat is needed.

Perry

Brad White_9

Your points have merit

but I would add that these internal loads and thermal flywheel effects are the reason that TRV's really shine. (Again, not that you intend or could install them, just a statement of principle.)

The heating curve relationship is an indirect one to room temperature, agreed. Universal control cannot take all local matters into account. However it gets the entire heating system to a managment point that is truly adaptable to fine tuning. That is really all that is left to do if OD reset is properly done.

BUT, by modulating the HW temperature based on ODT, think of how far you have gone to not only saving fuel but also in comfort? You have trimmed the fat from an unwieldy beast, tailoring the heat balance as best as anyone could.

Imagine conventional control with what you are saying: 180 degree water maintained all the time (for DHW or just because it wants to be available), then pulsing on a circulator for different periods of time to heat the house.

It will work, but with one thermostat running the circulator, how much will that care that you are roasting a mastodon in the kitchen while your western sun-baked bricks begin to radiate inward and the north winds whistle through your windows?

Your heating profile if graphed would look like a roller-coaster, spikes and bursts of heat between cooling cycles. With OD Reset and especially modulation, you are looking at a flat-line temperature gradient. Such a deal.

Now, as for boiler control of the circulator- no harm in that. In fact, the outdoor temperature likely is taken into account. Keep in mind though that at ODT's approaching 60 degrees or so, the HWS temperature will be very close to room temperature anyway. Room sensor influence can help but only in one room.

I guess my bottom line is, scenarios aside, there is a point when over-thinking happens. I go to the extremes sometimes, all of the what-ifs. But in the end, I avoid "Analysis Paralysis". The Vito concept we have been discussing does many things very well. The other parts are worth considering but I would not lose sight of what happens 99% of the time.

My $0.02

Brad

Mike T., Swampeast MO

You are very correct about other factors besides just outside temperature that affect the heating load. That's where TRVs really help as they do compensate for these factors. Yes, I realize that TRVs are impractical in your situation.

There is a room temperature controller for the Vitodens that allows room temperature feedback to modify the heating curve, but the literature recommends its use only for very low mass emitters like fin baseboard.

As I understand the Vitodens, there is no need for it to control the secondary circulator in your situation. Merely use the wall thermostat to control the circulator. As long as there is no secondary flow when the circulator is off (the Super Brute has integral flow checks), there won't be any heat leaving the LLH. With no heat leaving, there's no need for the boiler to supply heat.

Your goal is to establish a reset curve that allows for long calls for heat from the thermostat. Please believe me when I say that with even reasonable insulation and weatherization that it's quite possible to establish a heating curve that closely maintains the sun dial setting regardless of weather conditions. In moderate weather when load is below the minimum modulation level, the burner will cycle at minimum fire rather like a normal boiler (the cut-in and cut-out points do not [appear] to be fixed however).

You'll then set the wall thermostat at the level you desire. If daily setback is used, I would highly recommend the use of the built-in 7-day, multi-event timer as opposed to using the wall thermostat. If you find that recovery from setback is too slow you can use less setback and/or set back for shorter periods and/or increase the sun dial setting.

If you want the ability to rapidly and significantly raise space temperature via the wall thermostat you will increase the sun dial setting. Note however that you can do the exact same thing by going to the boiler and increasing the sun dial setting only when you want this ability and putting it back to normal when such is no longer needed. The former is more convenient, the latter significantly more efficient for those times that you don't need the ability (likely most of the time).

During moderate weather when you just don't the heat to run and don't mind the house getting a bit cool, merely turn down the wall thermostat significantly.

You operational sequence is reasonable BUT 4) Heat loss in LLH cools off water. Vitodens controller senses low temp point and starts boiler and sets boiler temp as per curve. Boiler circulator pumps circulates some water through house radiators heating houase--even when not called (and manybe when not needed due to warm day). house warms up some... (even if only a little). This will NOT occur! The boiler circulator is incapable of moving water through the secondary side of the LLH and the flow checks in the secondary circuit prevent "ghost" flow.

Consequently, #5, #6 and #7 will not occur either. The worst thing I can imagine is that the boiler would give an occasional "pulse" (a 2-3 second fire) as the water in the boiler and LLH cools significantly below reset target.

While I doubt this is truly needed, you could probably use a relay connected to the thermostat to shut down the boiler when the thermostat is not calling for heat. I can see at least two ways to do this, but am not certain of the effect on DHW production.

Perry_2

Real life limitations on Flow on the Secondary Side

Mike T supplied the basic equations for modeling how a Low Loss Header works and provided some theoretical calculaitons that make the temperatures reasonable.

I built a spreadsheet to model the boiler response to make the Low Loss Header work; and in it I inputed an assumed value of 15 gpm for my secondary side, and 5 GPM for the Vitodens 200 (6-24); with secondary side inlet temperature of 140 (return and boiler outlet mixed)and return temperature of 120.

This outputed a needed boiler outlet temperature of 180 F.

A variety of assumed flows and temperatures could be inputted and it all seems to work... OR DOES IT?

I knew that the spreadsheet was missing something - so I added a section on the heat load, and boiler rise - and bingo.... It doesn't work under the inputs I mention above - because the boiler would have to be outputting 148,100 Btu/Hr - and my current system cannot do that.

Changing the secondary flow to 10 Gpm at least theoretically works for my existing boiler at 98,760 Btu/Hr (I have not yet modeled radiator output - which will give me a better idea of how my current system is working - and a better idea of the actual flow in my system).

Just looking at the temperaturs are not enough; you have to pay attention to heat load and boiler rise. Since the boiler flow will be fairly constant based on the head loss of the piping and LLH; I have run a varitey of scenerios from 3 GPM to 5 GPM primary flow: I can see how it would work - as long as I have the right flow in the secondary loop.

So how much secondary loop flow do I currently have - and need? I'll keep plugging along...

I have attached the spreadsheet for those who want to play. I am sure that Viessmann and other boiler Mfr's have similar software.

Oh, the "E" in me took over and I checked how accurate the heat load calculations are because we are using assumed "constant" values that in reality change with temperature. The heat load calc is within 3% of actual.

Perry

Eddited to add: The forum downloads the spreadsheet file as a "cfm" file. Save it, then change it the file type to "xls" to get it to run as a spreadsheet.

Mike T., Swampeast MO

A variety of assumed flows and temperatures could be inputted and it all seems to work... OR DOES IT?

With a known flow rate and delta-t (e.g. output) on the secondary side, I believe there is only one combination of flow and delta-t on the primary side that allows boiler output to equal emitter output.

I didn't go through the regression in the example--just "homed in" by trial-and-error. Fortunately, I only had to make one guess and one re-calculation from the original trial.

6 gpm is plenty of flow to unload 90,000 btus and requires a quite reasonable 30° delta-t. "Reasonable" at least for radiators of nearly any form but perhaps too high for radiant floors and likely unachievable with bare-tube staple-up in real-world situations at high load as the 15° drop in average temp will have a significant affect on output ability.

Head loss in the secondary piping does of course reduce this flow abilility so that alone can require the use of the low-loss header even if the system can be satisfied with a max of 6 gpm or so.

What I'm 99.99% certain you will find is that the greater the fixed flow rate of the secondary exceeds 6 gpm (with correspondingly lower delta-t), the higher both the return to the boiler and supply from the boiler will climb in temperature. These higher temperatures will result in lower efficiency.

Sorry to keep repeating myself, but with your diverter tee system you will find that using the lowest possible secondary flow that maintains reasonable temperature balance in the home will result in the highest possible efficiency for the system as a whole.

When doing these sort of calculations you will find it MUCH, MUCH easier to work from the basis of "space temperature maintenance" where energy in is in close concert with energy out" and space temperature is steady. The Vitodens is DESIGNED AND BUILT to do just this. TRVs/FHVs and variable secondary flow or "direct drive" using only the built-in circulator are a significant aid to this goal, but not absolutely required.

If you work from the assumption of "turning the heat on and off to maintain a thermostat setting", these simple calculations are garbage as you've NEVER approached balance between boiler output and structure load.

Efficiency with a mod-con is ALL ABOUT achieving this balance and then modulating the flame as accurately and smoothly as possible to maintain the balance regardless of changing load (either from external or internal sources). Unfortunately this balance doesn't happen over night--nor does it happen in even a single solar cycle. Fortuntely with the Vitodens however, the very nature of the burner [appears] to be an aid to this goal.

Once you've achieved and maintained this balance you can further optimize a system using the LLH by keeping the secondary flow as close as possible to the primary.

Mike T., Swampeast MO

If you try similar (using the low-loss header concept) with fixed flow on BOTH primary and secondary side, I believe you'll find it impossible to achieve the sort of balance I speak of--even with a modulating burner. You won't be able to maintain a steady average temperature on the secondary side while at the same time matching boiler output to load.

Perry_2

I understand the concept - but I have to work with my existing

Mike:

I understand the concept of using the lowest water temp as reasonable and the lowest flows as reasonable on the secondary side. My point was that just looking at temperatures is not enough - you have to be looking at heat loads of those assumptions and comparing it to what the boiler load is under those assumptions.

The flow through the Primary boiler circuit will be essentially fixed once you pipe it up.

The secondary system needs a certain flow as well to work properly (sufficient flow to create the head losses in the diverter T's for them to work); and there will be a low flow limit for them to work.

What my modeling - using heat output and boiler rise as well shows is that my initial assumptions of 15 GPM (or more) through the secondary side has to be wrong. Now it might be 10 - or it might be less (but I doubt that it is less than 5 GPM due to the pump curve).

By paying attention to the total heat output you can see if your assumptions work or not. I have in fact played with a number of other scenerios - assuming 10 F drop in the system and other flows that may be more typical of a system that is on modulating boiler output.

As I see it, the modulating boiler output will only apply consistenly during the 4 coldest months of the year. The other 4+ months the boiler will cycle on and off because its lowest firing rate will be more than the required heat load. In this case, the boiler will essentially need to be controlled by thermostat. Letting it run at minimum and continued heating of the house way beyond comfort levels (or am I supposed to open my windows) is not realistic. (truth be told - it would be much better in my case if there was a Vitoden 3-12 model); and I installed two of them (or some other back up heating source for really cold days).

I will be doing some modeling on what the radiators put out and see how it matches my memory of how the system temperaturs cycled (I had thermometers on it for about 4 months).

That will give me a better outlook.

I have no doubt that this system can be converted, and converted in a way that greatly increases efficiency. But we need to understand how the existing system actually functions now in order to ensure that the modification works.

I should also mention - that knowing that the current system flow has to be less than 15 GPM, allows the corect sizing of the LLH.

Perry

Mike T., Swampeast MO

I'll shut up soon--hard to stop when I get going...

Many may think that the point I'm trying to make about matching boiler input to load as closely as possible is impossible with "minor" points like trying to keep secondary flow as close to primary and keeping daily setback to an absolutely minimum unnecessary.

Granted, my information comes mainly for a single converted gravity system with TRVs and Vitodens without LLH, but it's not operating in the twilight zone and I have added radiant floors as well--just currently small ones.

What I have found is that the closer I get to the ideal system where energy in = energy out, the more the individual measures reinforce each other to keep the system in balance.

I improved my heating system for over 10 years before finally replacing the boiler. Typically oversized semi-modern cast iron replaced with a Vitodens. By the time the Vitodens was installed the rest of the system required no modifications. What I had found was that each improvement I made did help some, but not as much as it should. Why? Because each of the improvements had a corresponding efficiency "hit" on the boiler. While I was certainly reducing weather adjusted seasonal fuel consumption, boiler efficiency was actually falling!

As best as I could estimate, I was operating with a seasonal and SYSTEM efficiency of only about 43% with the old boiler and fully "improved" system.

With the Vitodens and optimizing its operation the seasonal system efficiency appears to be about 95%!!!

If I ever get solar integration to the system (my own design), I expect 98+% percent seasonal and system efficiency PLUS reduction of overall fuel consumption for space heating by 20%-40% depending on the weather. As a bonus fuel consumption for DHW should easily be reduced by 75% compared to the current stand-alone 90-gallon gas fired heater.

All of this, including a planned and much larger radiant floor, will be accomplished with just the single circulator built into the Vitodens plus a TINY circulator for the solar panel to HX coil loop.

Impossible for me to calculate cost-benefit other than to say "quite good" and "very good" if the starting point is an old two-pipe gravity system in substantially original condition.

Mike T., Swampeast MO

The flow through the Primary boiler circuit will be essentially fixed once you pipe it up.

No. The Vitodens will vary the speed of the circulator to achieve the flow rate required to meet the current supply target while meeting the final goal in that LLH illustration. Namely, "energy supplied by boiler = energy consumed by system". This is inherent to the operation of the system when the circulator is in "boiler circuit mode". The lower the primary temperatures required to achieve this, the closer you get to energy consumed by the boiler = energy consumed by the system.

The Vitodens [appears] to be unique in this regard. You simply cannot think of the Vitodens in normal terms. The only way I know to truly understand it is that it's designed to achieve the impossible as closely as possible.

If you begin by assuming that it has achieved the impossible, namely energy in = energy out, then you'll find three main routes for inefficiency and also see the ways to reduce such to the highest possible degree given system design PLUS see how all three interact...

1) The first route for inefficiency is flue loss. This is minimized simply by operating at the lowest possible supply/return conditions in the boiler with preference given to minimum return.

2) The next route for inefficiency is deficiency of the emitters. They must be capable of instantly absorbing the whatever output of the boiler is required while maintaining space temperature in the coldest weather using a BOILER temperature that CANNOT exceed 167°F (75°C). Most emission systems won't have a problem with this--most problematic will be bare tube "staple-up" or suspended. This inefficiency is reduced in two ways: decreasing the average required emitter temperature by increasing the size of the emittter and increasing the ability of the emitter to liberate heat from the water (e.g. putting that bare tube in highly conductive heat transfer plates). "Oversizing" radiators does the same thing. The lower the required operating temperature and the higher the heat flux, the more opportunity you have to further reduce #1 (flue loss) by operating with less and less flow and more and more delta-t. TRVs/FHVs do this automatically.

3) The third major route for inefficiency comes through on-off operation of the system during periods when heat can be supplied constantly at just the required level to maintain interior conditions. Replacing 400,000 lost BTUs over 10 hours as they are being lost is significantly more efficient than replacing them in say four batches of 100,000 btus. Why? Because those batches MUST be supplied at higher temperatures because you are supplying them in excess that REQUIRES A HIGHER EMITTER TEMPERATURE. This certainly impacts 1) and can easily impact 2) as well by exceeding the capacity of otherwise perfectly suitable emitters! Again, TRVs/FHVs are a WONDERFUL way to solve this problem as they will vary the system flow to maintain the emitters at the lowest possible temperature to just replace the BTUs being lost. Without TRVs, you MUST optimize the supply temperature such that any thermostat(s) remain "unsatisfied" by staying within their hysteresis range as much of the time as possible.

There is a fourth major cause of inefficiency--THE USER. Unfortunately this cannot be "controlled" but it CAN BE EDUCATED! A new generation of control may be forthcoming that automatically allows the system to maintain the highest possible efficiency while allowing the highest possible versatility given the nature of the emitters and of the shell. Cross your fingers--I'm working on such...

Perry_2

\"Heating\" system efficiencies

Mike:

I did not confuse and equate energy in versus energy radiated out by the system. What I equate in my spreadsheet is that boiler energy out = heating system energy.

I fully understand that more fuel energy is used - and the sources of the losses.

If this were a 2 pipe system I think some of the issues I see would not exist. Instead I have a 1 pipe system - and it nor the cast iron radiators isn't going to be changed.

The other problem is that dispite the attemps at better matching the boiler load to needs - that it may well be that the Vitodens 200 - even in it's smallest size is substaintially oversized for my house. I believe it was Brian who estimated that my real mid winter heating load was in the range of 30,000 to 40,000 Btu/Hr. Thus, much of the year my neads may well be below the lowest firing level of the Vitodens and require the boiler to cycle just like the current boiler (and a number of other Mod boilers I have looked at; only the Muchkin goes lower - but not that much). Of course the extra capacity makes DHW supply easy.

Yet, I believe that the Vitodens 200 (or something similar)is probably the best way to go (as long as it does not cost a lot of extra money). At least I get a modulating boiler for the coldest time of the year when the most heat is used, and the boiler can fire at its lowest rate for cycling operations.

With a larger house - and a larger heat load things would be easier. I mistakeny previously listed my house as 1700 Sq Ft (typo). In reality, its about 1300 Sq Ft. I've also done a lot to seal up leakage - and believe that I can seal up another 10,000 Btu/Hr in the next year or so.

Too bad there is not a Mod-Con that fires down to 10,000 or 12,000 Btu/Hr.

Perry

Jed_2

What if

"Do however imagine what happens when secondary (emitter) flow greatly exceeds primary (boiler) flow. Delta-t through the secondary will decrease as flow increases--thus more and more return water mixes into the supply stream. The internal temperature of the boiler will have to increase to maintain target at the LLH sensor location. This will somewhat reduce efficiency compared to a situation where secondary flow is closer to that of the primary. This is why I suggested the "Super Brute" or similar and to first try the lowest possible speed."

Mike, what if that secondary (system) circulator was a variable speed delta T circulator, as in the taco 00VS set up to maintain delta T, based on system emitter output and SWT? You would now have a balance between the boiler modulation and system return temp/flow balance. With or without TRV's, system flow will ramp, even on cold system start, coupled with the Vito's reset curve and immediate response, to maintain the boiler return temp requirement.

Jed

Perry_2

Missing Link - Secondary Flow issues Resolved

Now that I have seen a few of the manuals for the Vitoden 200 - and how it is connected to a Low Loss Header.

In a case like mine: with a single heating loop (monoflow T's) with a single secondary circulating pump...

The Vitoden controls the secondary circulating pump directly using an expansion board, and connector cable, in the Power Supply Module.

The Vitoden monitors room house temperature through the WS remote control unit - and fires and circulates, or idles, as necessary to control house temperature in the cases where heating load is less than boiler output.

The WS control unit also handles automatic daily house temperature setback as programmed.

Simple - when you can finally connect all the pieces.

I note that it is also possible to connect a second lower temperature circuit with a boiler expansion board, control valve and other pump (controlled by a RS controller) to the set-up above.

I'll hold this second circuit in reserve for basement heating if I ever need it (I figure I have at least 40 Sq ft of steel radiator in the basement - from the 1 1/4 piping and 1/2" branch piping (uninsulated) in the basement ceiling. No wonder it never gets cold down there in the winter.

Perry

Mike T., Swampeast MO

Jed:

I sincerely cannot answer that question.

My gut instinct however is that constant delta-t is a poor way to modulate a variable speed circultor in space heating applications.

Mike T., Swampeast MO

Perry:

You're trying to turn the Vitodens into a "traditional" boiler by using controls that will not take advantage of your generously sized cast iron baseboard.

This [mainly] seems because you are stuck in the ways of your current thermostat control strategy.

You can turn the Vitodens into a fairly "dumb" boiler and even defeat the 75C limit but such is completely contrary to the design as the Vitodens does its best to maximize SYSTEM efficiency.

Perry_2

I'm trying to figure out

how not to overheat the house when the heating loads are below 22,000 Btu/Hr.

At 50 F outside air temp according to the charts with a reasonable guess for the curve - this thing is just going to keep heating the house by circulating 100+ F water -contstantly.

What drives it to shut off - Apparently only the outside air temp going up.

If its a sunny day in the spring or fall with the sun out - I won't need much (if any) heat due to the thermal gain from the front windows during the day.

But, it seems that the Vitoden could care less and it will keep pumping heat out through the radiators (remember I do not have RTV's and am not retrofitting them due to the design of the baseboard): It dosn't know about how much solar gain I'm getting.

So how do I keep from overheating the house in cases where I don't need much heat load? Really.

I know- I'll open the windows!

Opps... I may have forgotten to mention that I can't due that due to my asthma the the idiots with the wood fires in their backyards in the area.

Sorry folks; but I'm not trying to defeat the base function of the Vitoden 200 where it only supplies the needed water temperatures to heat the house when it needs heat. I'm trying to figure out how to shut off the heat when it is not needed (especially when the heating requirments are well below minimum boiler load).

Can anyone tell me how to do that without just shutting the heating portion of the boiler off?

Perry

Perry_2

Design of Vitodens Vs Conventional Retrofit - An Issue

I woke up in the middle of the night with this realization:

VITODENS 200:

The Vitodens 200 is set-up to work on a system where most - if not all - the radiators are individully controlled by TRV's. As such, the Vitodens or the secondary loop circulates appropriate temp water that is used, or not used, as needed based on the temperature in the room. The TRV's prevent rooms from overheating due to their built in thermostat.

The night setback, vacation mode, freeze protection all works because the TRV's are wide open calling for more heat in the rooms - so that a properely set curve allows the Vitodens to lower the house temperature by just using the setback curve temperature water in the heating loop.

A properely adjusted Vitodens circulates water (constantly) based on the setback curve programmed.

If you do not have TRV's installed on your radiators - there is no way to limit the room temperature; and there is not a conventional thermostat feedback to the Vitodens 200 system (or at least I have not found one - yet).

CONVENTIONAL SYSTEM:

Thermostat controlls the circulation of warm water through the radiators. Boiler fires based on return loop temperature and min temperature setting for boiler - but only if the circulator is running. I.e.: No call for heat - no need for the boiler to fire.

CAST IRON BASEBOARD:

Cast iron baseboard may - or may not - be easily adaptable to TRV''s depending on design and installation. The ones that are floor level - have covers over the ends so the piping and throttle valve - have inlet/outlet piping on the bottom connection (hugging the floor) may be difficult to adapt to RTV's.

Higher cast iron radiators - with supply piping extending up from the floor - may be relatively easy to adapt to RTV's.


MY SYSTEM - Retrofit Possibilities:

My house has low CI Baseboard. I've now opened and pulled off the end covers on one of the units. The existing inlet throttle valves are threaded into a 1/2" NPT (female) - 3/4" NPT (male) adapter at floor level. Not saying that it could not "theroretically" come appart - but; I'd not want to bet on it given that these things were assembled over 50 year ago. Something goes wrong and you are digging into the floor and the cieling and walls below... Not sure how you install a TRV and reinstall the covers over the ends (and there is nice molding arround the top of the radiator and cover: It would look really bad to just toss out the end covers).

I did find out that a number of the throttle valves are frozen in position; which I doubt is full open. That may be the ultimate root of my very cold weather heating problems (a issue I will take up with the heating contractor to see what can reasonably be done).

Also, I do believe that the Monoflo system needs to have flow throught the radiators in order to maintain normal system head. Installing RTV's that shut off radiators when things were warm might prevent proper heating on the rest of the system where needed as the pump deadheads. This issue may not exist for 2 pipe systems.

Thus, it appears that my system is best controlled by a thermostate.

Either the Vitodens 200 can be somehow tied to overall thermostat control - or it can't be. I have no problem with it circulating lower temperature water as per a setback curve when heat is needed. I can see the benifits of modulating firing with the setback curve. But, how do you control and limit room temperature without RTV's: especially on low or no heat needed days due to solar gain.

Perry