Vitodens / Unico configuration

Mike T., Swampeast MO · March 2006

You could have the Unico circulator run constantly for the freeze protection. Temp going through the coil (when the fan isn't running) would be that of HCA. This won't "rob" heat from the TRVs--the boiler will just have to produce a bit more heat to keep the Unico circuit up to temp.

In other words, the heat lost by keeping the Unico coil and piping warm will create a load--the load will try to reduce the supply temp below target. When that happens the boiler produces more heat to maintain target. The TRVs will be utterly unaffected.

Have not used, but as far as I can tell, the first mixing valve (regardless of Vitodens model) is part 7133 392

Are you talking about expansion board 7134 211 ? If so, my literature doesn't show it having anything to do with a mixing valve--description is "for failure output (dry contact)" Sounds to me lik all it does is close a normally closed relay contact if the boiler should fail thus allowing some action to be taken (provided you have power for whatever takes that action). I have no idea of the exact definition of "failure". It is listed as applying only to models without a built-in circulator.

Expansion board 7134 209 provides the failure output and a secondary circulator pump output (120 VAC 2.0A max). It is listed as applying only to models with a built-in circulator.

The mixing valve controller 7133 392 provides a circulator output for the associated pump (after the mixing valve).

System Layout 3 shows the circulator for the panel circuit connected directly to the boiler.

As to the Unico circulator? Wouldn't be a problem if you didn't need freeze protection as it would only run the Unico thermostat calls for heat--thus it wouldn't be connected to the Vitodens system in any way. Makes sense with the idea of it operating as an "external call for heat". The appropriate expansion module [might] provide the necessary control for this circulator--provided it has power whenever the Vitodens is running. Otherwise use a double-pole, double-throw relay and an outdoor temp sensor to control the Unico circulator.

Simple schematic attached:

Drawn in "freeze protect mode". Once outdoor temp rises above 40° (or temp of your choosing), the normally closed contact opens and the pump stops.

When the Unico t-stat calls, it energizes the relay coil and the Unico circulator gets power regardless of outdoor temperature.

The 110VAC is regular line power--NOT from the Vitodens.

Dave_4 · March 2006

Vitodens / Unico configuration

Hi.

Warning... this is a long story :-)

First let me say that I am not a plumbing or electrical professional. I am a Software Engineer. I am working with professionals to check my work, do the gas piping (that's something I won't do) and deal with inspections. I'm not trying to be cheap, its just that I love doing it. In my next career maybe I'll be a plumber/electrician specializing in these kinds of installations.

I am in the process of converting the mechanical system of my home. The home was built in 1996 with a FHW system based on a Burnham Spirit 96K BTU natural gas boiler, a 41 gal. Boilermate, and baseboard radiators between virtually every window in the house except in the corners. There's roughly 2000 sq. ft. of living space on 2 floors. Full basement and walk-up attic.

A few years ago we wanted to get central air and start finishing the basement. We installed a 3 ton Unico system, single zone feeding the whole house, 12 outlets upstairs, 10 outlets downstairs. At the same time we decided to remove the radiators which were always in our way of putting furniture where we wanted it, and always "falling apart" if you knocked into them the wrong way. Since we were installing the Unico, I got the heating coil as a temporary measure between the time we removed the radiators and installed radiant heat on the first floor, in the basement, and in the second floor bathrooms. In addition, the original mechanical installation left exposed pipes, gas lines and boiler air/vent ducts all over the place in the basement. I was not interested in the significant amount of soffiting that would be required. I wanted the basement to look like the rest of the house. So we also decided to go with the Vitodens boiler, not only for its concentric zero-clearance ducting that I could put into a joist bay, but for its energy conservation properties as well. We also practically redid all the gas/water/drain plumbing in the basement (also added rough plumbing for a basement bath). Lots of work.

My interim solution included a tekmar 361 based injection weather responsive system (mostly because I thought I would carry this forward into the radiant system - that was before the Vitodens decision was made) for the Unico, mixed down for the radiant in one of the second floor baths (the one that I remodeled and included multicor in a mud floor under slate).

The current status: The Vitodens installation is complete. Photos at http://howieb.smugmug.com/gallery/1246569. The Unico heating coil is still the only source of heat. The pump feeding the Unico runs constantly. I thought I could get away with only the radiant heat as I mentioned previously, however my kids have been complaining on cold mornings even with the Unico, so I'm thinking I'll have to either continue using the Unico (or install some Runtal or equivalent (suggestions?)) just for early morning heating in the bedrooms, the implication being that I will have a high-temp circuit in addition to the radiant. I have recently ordered the expansion board and mixing valve kit for the Vitodens.

My questions involve the Vitodens configuration and some of the controls wiring. This is how I think the system should work: HCA, the high-temp cicuit, would always be set back (to an equal or lower heating curve than HCB). HCB, the radiant circuit, would be on during the day, and (maybe) set back at night. The Unico thermostat is currently in the upstairs hallway. If I add bedroom radiators, I would install a thermostat and zone valve for each bedroom. The Unico coil would act as a bypass if all the zone valves were closed and the pump went on (for freeze protection). I would also connect the thermostats to a relay whose NO would be connected to the Vitodens "External Change of Heating Program" X4.1/X4.2. This way, if there is a call for heat in the bedrooms or by the Unico, the boiler temp would be forced up and the pump would go on for HCA. The mixing valve for HCB would then close to adjust the temp for the radiant circuit.

The tricky part that I don't fully understand is how to ensure that whenever the Unico fan is running and there is a call for heat, that there is in fact hot water in the Unico coil. Since I have the Vitocell connected to the DHW on the boiler, the boiler will sometimes switch over to the DHW and the Unico will be cold. One very helpful contractor told me that plug #20 (L) on the Vitodens expansion board can be connected to a Taco SR504. However he laid it out such that the SR504 would energize the pump. I'm thinking that the purpose of the 504 will be to energize the fan when there is both a call for heat and the pump is on. This is not quite how he told me to hook it up, but I didn't discuss the need for freeze protection, i.e. having the pump run when there is no call for heat. I actually have no idea if the SR504 can function this way... I'm assuming that the #20 input functions as another signal required in addition to a zone input to close the end switch and energize the related zone's output. In addition, I need to make sure the pump is running when the fan is manually turned on at the thermostat (for filtering) so that the coil has at least marginally heated water. For this I introduced an SR501 that switches between the expansion board controlled pump-on and a fan controlled pump-on.

I guess my questions are, is this reasonable and correct, or is there a better way to get what I want?

This needs a picture... I uploaded a wiring diagram to the same place as the pictures. If you find this hard to read, it might be easier to download the file to your computer. Here's a direct link to the picture, and the description: http://howieb.smugmug.com/gallery/1246569/1/59995330, http://howieb.smugmug.com/gallery/1246569/1/59995332. I can also send you a .ppt (microsoft powerpoint presentation) which is much easier to read.

Thanks in advance for your help.

Dave_4 · March 2006

I didn't realize I could include attachments....

Here are a few of the items from smugmug.

Paul Pollets · March 2006

One problem...

is the piping sizes must be increased to 1" under the boiler, to the DHW tank and the LLH, per mfg. instuctions. (Often 11/4" to the low loss header)

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

Dave_4 · March 2006

Yes...

Gary Wallace pointed out the sizing issue to the DHW, which I plan to fix. Gary is local, and was recommended by the folks who did the piping design for me. He recommended I post to this forum.

I didn't know there was also an issue with the piping to the low-loss header.

Mike T., Swampeast MO · March 2006

Those drain connections for condensate, T&P, etc. are downright sexy!

The rest of the system goes "cold" during a call for domestic hot water by design. This is called "DHW priority" and is a completely intentional function. The logic is that the DHW call is rapidly satisfied by receiving the FULL "attention" and usually full output of the boiler. Since the DHW call is satisfied rapidly the house doesn't have a chance to cool to any degree.

Keeping the circulator supplying the Unico coil running constantly is somewhat of a waste as even when the blower isn't running the coil is being heated and the boiler is supplying energy to keep it heated. You really only need to run that circulator when the Unico itself is running--e.g. when the thermostat is calling for heat. To prevent a "cold air" problem when the boiler diverts itself to DHW production, I would install a simple strap-on temp sensor with switch on the supply pipe from the Vitodens (on its' side of the LLH) in series with the thermostat. That way, when the supply pipe goes cold during DHW production, the heat call to the Unico will be stopped. (There could be other ways to do this--much depends on what kind of outputs are provided by the Unico unit itself.)

Don't forget that the "real" Vitodens way uses proportional control of space heat--not binary wall thermostat operation. This makes for some difficulty or confusion when attempting to "Americanize" the operation...

Before I go on, I need to ask a few questions.

You say that the kids complain on cold mornings. Are you using night-time setback?

What type of heat transfer method do you plan to use for the radiant floors? I presume the radiant won't be in the bedrooms? Is the radiant just for small spaces like bathrooms with the transfer method you mentioned?

What are your current reset curve and sun dial settings? I presume you're not using the "external call for heat" function to operate the Unico, correct?

Dave_4 · March 2006

> Here are a few of the items from smugmug.

Dave_4 · March 2006

> Those drain connections for condensate, T&P, etc.

> are downright sexy!

>

Thanks!

> The rest of the system

> goes "cold" during a call for domestic hot water

> by design. This is called "DHW priority" and is

> a completely intentional function. The logic is

> that the DHW call is rapidly satisfied by

> receiving the FULL "attention" and usually full

> output of the boiler. Since the DHW call is

> satisfied rapidly the house doesn't have a chance

> to cool to any degree.

>

I set the DHW temp to 140. I have a thermostatic valve set to 120. We will have three full baths, and two teenagers. Usually at least two showers in quick succession and sometimes a third simultaneously. The thing is, if the Unico is blowing, the air will turn cold as soon as the DHW solenoid is enabled. The Unico is in an unheated attic, and things do cool rather quickly.

> Keeping the circulator

> supplying the Unico coil running constantly is

> somewhat of a waste as even when the blower isn't

> running the coil is being heated and the boiler

> is supplying energy to keep it heated. You

> really only need to run that circulator when the

> Unico itself is running--e.g. when the thermostat

> is calling for heat. To prevent a "cold air"

> problem when the boiler diverts itself to DHW

> production, I would install a simple strap-on

> temp sensor with switch on the supply pipe from

> the Vitodens (on its' side of the LLH) in series

> with the thermostat. That way, when the supply

> pipe goes cold during DHW production, the heat

> call to the Unico will be stopped. (There could

> be other ways to do this--much depends on what

> kind of outputs are provided by the Unico unit

> itself.)

>

Agreed. Ideally not only would the pump for the Unico only run when there is a call for heat, but also when the fan is on for filtration (more likely during transition periods, but even more likely for filtration all year round once the radiant is complete). When the fan is on, and there is no call for heat, the Vitodens would run at the OAT controlled temperature with a curve equal to the radiant curve. To provide comfortable air, but not heating. That's why the complex wiring... I think it fulfills all my requirements.

> Don't forget that the "real" Vitodens

> way uses proportional control of space heat--not

> binary wall thermostat operation. This makes for

> some difficulty or confusion when attempting to

> "Americanize" the operation...

>

Yes. I feel unclean :-) installing thermostats for the bedroom radiators (if I indeed go that route). However, the way I look at is that this allows the Vitodens to spend much more time at a lower curve, rather than the higher curve required by the radiators, even if the radiators are used only 1/10 of the day, and potentially at unpredictable times. Does that make sense?

> Before I go on,

> I need to ask a few questions.

>

> You say that

> the kids complain on cold mornings. Are you

> using night-time setback?

>

I am. My wife has allergies that often turn into chronic sinusitis and brochitis. She cannot live with the Unico running at night. I have it set back to about 65 (not that low actually) so it hardly ever runs at night. Goes to 70 at about 5:30am (I moved it 30 minutes earlier because of the kid's complaints), 68 during the day, 70 in the evening, and 65 at night.

> What type of heat

> transfer method do you plan to use for the

> radiant floors? I presume the radiant

> _I_won't_/I_ be in the bedrooms? Is the radiant

> just for small spaces like bathrooms with the

> transfer method you mentioned?

>

The entire first floor will be radiant, staple up with thermofin and thinfin, 6" OC. The basement will be radiant, 12" OC custom plywood and plates. The second floor has two bathrooms, one has radiant in a mud floor, but it is currently not connected, and the master bath will be remodeled after the basement is complete, probably also with tubing in a mud floor. There will be four manifolds. One for the basement with a zone valve to prevent overheating. Two for the first floor, one for the thermofin area, and one for the thinfin area, and one for the 2nd floor bathrooms, for which I think I'll have a manual three way mixing valve to keep the temps proportionally lower.

> What are your

> current reset curve and sun dial settings? I

> presume you're not using the "external call for

> heat" function to operate the Unico, correct?

Well, currrently, since all I have running is the Unico, I'm on a 2.0 curve. The sun dial is centered. Once the radiant is in, I'll be on a curve that tops out at about 125. Is that like 1.0, or 1.4? I'd have to look a the book.

Thanks.

Mike T., Swampeast MO · March 2006

I'll elaborate more later, but here's the first recommendation:

Your wife's allergies (I've been fighting that EXACT same problem all of my life) will LOVE an OVERSIZED TRVd radiator!!!

Your Unico heating coil need not go to waste--even though high-velocity air = low volume.

Considering your ultimate plans, I believe the Unico can be used for a relatively fast recovery using that dreaded "external demand for heat" function. To do this however the REST of the system needs to be the "Viessmann Way"!!!! You've purchased all of the needed Viessmann components--you just need to implement some more of the "grand plan". You can do this in stages, but you won't realize the best economy until everything is complete. The key is to use the Unico ONLY when you REALLY want or need it. But I will say that the more you use the Vitodens way they less you'll need your Unico for heating...

Mike T., Swampeast MO · March 2006

One other thing:

You'll find the cost of a TRV in a new installation HIGHLY competitive with a zone valve and wall thermostat! Even at US pricing where we pay a premium because of low utilization of TRVs! Multiple zone valves and binary (I've been corrected NOT to call them "digital") thermostats create absolute CHAOS for a modulating boiler. Modulating boilers want (dare I say "need") balance. With modulating control of the emitters, modulating boilers create their own balance from the chaos of the world. Their ONLY flaw is their inability to understand the changing desires of the occupants while simultaneously giving the utmost efficiency.

Dave_4 · March 2006

I'll wait patiently for your elaboration :-)

Consider - a trv'd radiator without a wired thermostat will require that the Vitodens run at a higher temperature so that the hot water is available when you turn the knob, yes? I would think that's bad, unless the heat loss is so insignificant when the radiators are off as to make the actual cost of running at a higher temperature insignificant? It would certainly reduce the cost of the install.

Mike T., Swampeast MO · March 2006

Not just the DHW. Even though ALL connections are 3/4" you're well behooved to increase the pipe size as soon as possible once you're away from the cluster-f#(* of the four connections.

Dave_4 · March 2006

> once you're away from the cluster-f#(* of the four connections.

Not sure I understand what you mean... how do I get away? Oh, you mean don't get 3/4" thread to 1" sweat, but transition to 1" further away from the boiler?

Mike T., Swampeast MO · March 2006

Oh, you mean don't get 3/4" thread to 1" sweat, but transition to 1" further away from the boiler?

Exactly. Depending on the layout a short section of 3/4" with perhaps a pair of 45s might give you a bit of needed clearance right near the boiler.

Mike T., Swampeast MO · March 2006

The elaboration is the answer

Your present problem is that you're recovering from setback while you experience peak domestic hot water demand.

Peak demand is currently high so use the DHW timer to raise the storage temperature considerably before you begin recovery from setback.

This should solve the current "cold air" situation.

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

Install your panels for the 2nd floor with TRVs in a separate circuit. Size them for about 160°F average water temperature at design loss using manual-J based calculations. You can oversize panels to achieve a trump over response in the rest of the circuit. Keep your trump card at ¼ or less than the total loss.

Supply the underfloor via your mixing valve and accessory circulator.

Set your curve to barely maintain the minimum acceptable temperature via the panels and floors.

The high-velocity air system becomes an external call for heat. Much like a call for domestic hot water you can use the external call to temporarily divert output. The TRVs and the mixing valve will both divert the heat not required to maintain their setting to the Unico. You'll be able to raise air temperature with relative speed.

Best of both worlds.

Dave_4 · March 2006

a little confused...

Changing the timer was the very first thing I tried, and that helped. Of course, nothing prevents additional DHW production, and cold air, during shower recovery. This is more likely to happen on colder mornings. This morning for example, the OAT is about 27, Unico started at 5:30, and now at 6:45 (shower time) the temperature is only 67 on its way to 70. This is a temporary problem though, and will mostly disappear at least at this time of day when the radiant/radiators are installed.

The thing I'm confused about is the "directly connected" radiators. I think you are saying that the HCA curve should be high, while the HCB curve should be correct for the radiant. Otherwise I'm not going to be running temps any higher than 125 through the radiators. If the HCA curve is high, then I'll have to set the timer for that curve such that heat is available anytime someone might turn the TRV, meaning that the Vitodens will generally be running at a higher temp, whether the TRV is on or not?

Mike T., Swampeast MO · March 2006

What time did you schedule the DHW boost and to what temperature?

Check out System Layout Five in the Technical Data Manual.

The panels (WITH TRVs) are directly connected to the boiler and operated by the built-in circulator. This will be your high-temp circuit, but if you follow the suggestion to size the panels for 160° average water temp based on a Manual-J loss calculation, your "high temp" circuit won't really be very high--particularly if you carefully set the curve so that you just barely maintain the minimum acceptable temperature in the space with panels.

The underfloor connected via the low-loss header, mixing valve and dedicated circulator. Considering your heat transfer method it will be runnning at a lower temp than the panels. Again, you'll want to set the second curve for this circuit to just maintain the minimum acceptable temperature.

Use VERY little setback or no setback for both the underfloor and TRVd circuits. This way, the boiler will be operating at the minimum possible temperature with the maximum possible efficiency to provide your "base" level of heat.

Pipe in the Unico circuit (with its' own circulator) AFTER the low-loss header, but BEFORE the mixing valve.

Hook up the Unico so that it makes an "external call for heat". With an external call, the boiler fires to a fixed supply temperature of your choosing--I believe you can even go above the normal high-temp limit up to 180°F using the external call.

Use the Unico in the morning or at other times when you want a relatively quick boost in room air temperature. The TRVs of the panels will just close themselves further to compensate for the increased supply temp produced during the external call. The mixing valve [should] still modulate to produce the curve of HCB. (Verify that with Viessmann--I'm not 100% sure about that.)

Because the Unico is hooked up after the LLH but before the mixing valve it will have access to the fixed hot water temp produced by the external call.

Prior to a call by the Unico, the boiler will be purring along at modulation (or cycling in moderate weather) to just maintain the minimum acceptable temp in the house.

When the Unico calls, the burner will jump to full fire to increase the temp. The difference between the prior (maintenance) level and full output will be the boiler power available to the Unico. While I don't know the outputs of your Unico nor the incomplete portions (RFH and panels) of the system, I would imagine that this difference will be sufficient in much? most? weather. IF the difference is not great enough, you can have it disable the underfloor circuit circulator when it runs--this will divert even more power to the Unico, but since the underfloor has been maintaining conditions and the Unico is only used for a relatively short air temp boost, the floors shouldn't cool appreciably.

This is what I meant by "best of both worlds". You can operate the underfloor and panels for exceptional efficiency and maximum condensation then (without any intervention other than turning up the Unico thermostat) get a relatively quick boost of air temp. While efficiency will drop when you're doing this, it always drops when you raise space temp. BUT you won't have to use higher-than-necessary curves (to allow rapid response for the floors/panels) during the great perponderance of time that the Unico is NOT calling.

Of course a call for DHW production while the Unico is running will still cut off the heat to the rest of the system. With careful adjustment of the DHW timer and DHW setpoint I believe you can eliminate this problem in most cases.

p.s. If I had physical room for the heating module in my Unico setup, I probably would have done very similar in my own system. Instead I used a heat pump for the Unico.

Mike T., Swampeast MO · March 2006

Still Need an Answer

You only gave me half of the heating curve--the slope.

What is the current shift setting? It should display in degrees Centigrade.

Dave_4 · March 2006

Sorry...

The shift is 0, i.e. there is no shift. I thought shift was something you adjusted after the system was in use. I guess I thought I wouldn't bother until the system was completely up and running.

Mike T., Swampeast MO · March 2006

No apology necessary!

So, your target this morning was around 150F. VERY high by my measure but perhaps low considering a hydro-air system recovering from setback...

Where are you located?

With the present system you [might] want to set your Sun dial VERY high and time it JUST for the morning "rush".

Once your final plan is instituted your base temperature requirement will PLUMMET!!! The slope will be much more shallow, but you may well have to add some shift.

Dave_4 · March 2006

Couldn't stand the depth...

So I replied to the first post...

Mike,

I live in Massachusetts.

I don't want to appear impertinent, but there are a few things I still don't completely get.

I think that the radiator usage will be unpredictable. They could be required at various times during the day, but overall probably a very small percentage of the day. In order to satisfy a potential radiator demand, I will have to run a higher curve on HCA than on HCB virtually all of the time. The Vitodens will also turn on the Unico pump whenever it thinks HCA needs heat (according to the timer, OAT and supply temp? or just the timer and OAT?) w/o Unico demand, bleeding off BTUs unnecessarily (into the unheated attic).

On the other hand, if the radiators are on the same "demand only" circuit as the Unico, then the boiler will run at a higher temperature, albeit a fixed higher temperature, only when required. The downside to this approach is that there is no curve, but is there really a downside to a fixed higher temperature? The upside is that there will never be a temperature so low as to not allow the radiators to function properly. In either case, the boiler will modulate based on the delta-T. If the demand involves only one radiator on a moderate day, then the delta-T will be low. If the demand involves all the radiators on a cold day, the delta-T will be higher, the boiler will work harder, but still modulate. In either case though, won't the boiler still find it's sweet spot during and based on the demand? Or will the demand disappear before it can?

The installation cost is higher for the zone valves and thermostats, but I think the "comfort level"... heat when I want it, might be higher.

UNLESS you think it's really just fine to run the boiler at potentially 40 degrees higher than it needs to be most of the time. Do you?

Thanks.

BTW, I really wanted some feedback on the wiring and if it will accomplish what I wanted, whether or not we actually end up there :-)

Howie

Unknown · March 2006

Mike, why size for a 160? With panel radiators, you could size for 140, 120, 110, 100... keep it "one temp" systemwide and be happy, oh so happy, la la la..

Unknown · March 2006

I'm still not understanding the assumption of high temp operation for the radiators. Size them properly and you will not need to go high temp. Set the TRVs, forget setback, and let them go.

Dave_4 · March 2006

OK

Assuming I can make it all one temp (except for the unico), can I just put the radiators on the same circuit as the floors? (only because I have really limited space right now for a takeoff before the LLH.)

In the second floor bedrooms, my heat loss (I think) is between 2900 and 3600 BTUs depending on the room. If we want to size it to 120, how big are we looking at? I was hoping to do verticals less than two feet wide, preferably 18" wide. Any brand recommendations?

Mike T., Swampeast MO · March 2006

I don't take that as impertinence--more as healthy curiosity.

I did give a wiring solution to your current problem in my original reply. I'm sure there are other ways. I'm not certain what (if any) leads are provided by the Unico heating coil. But, the circulator feeding the Unico should ONLY run when you want heat. I would imagine that there is a low-voltage lead from the Unico that goes "hot" during a heat call. Use such to operate a relay to turn on the pump. If you don't want to blow cold air during a heat call when the boiler diverts to DHW, things get a touch more complicated. Does the Unico unit not have a built-in function that will stop the fan if the heating coil goes cold and re-start the fan when it again heats? Very similar to a hot air furnace where the blower doesn't start until the HX is heated and continues until it's cool? If it doesn't you can replicate this function with an adjustable "strap-on" temp sensor with a single-pole switch. Best if you sense the supply temp on the boiler side of the low-loss header. Run the red "heat" lead from the thermostat through this switch. If the pipe is above the setpoint, the switch closes and the Unico gets its' heat call. When it goes colder, the heat call is interrupted until it again heats. You'll still be able to use the "fan" switch for air circulation if desired.

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

For the rest, I'm sincerely trying to give you a highly efficient "German" system with "American" adjustability and response at the lowest possible cost. You have nearly all the components you need--you just need the radiator panels (with TRVs) and the underfloor heat.

You may not understand thermostatic radiator valves (TRVs). Heck, a lot of heating pros don't understand them either...

A TRV is merely an adjustable valve with a built-in feedback mechanism--most usually the room air temperature. While a typical "zone valve" is either fully open or fully closed, a TRV is almost always somewhere in between.

Once the TRV is doing its REAL job--maintaining your desired room temperature--it admits just enough water to keep the radiator at just the right temperature to prevent the room temperature from either rising or falling to any significant degree. This is called modulating control.

If the water coming into the TRV is significantly hotter than needed to maintain your room temp setting the valve automatically closes further--thus reducing flow. While the temperature drop across the radiator changes, the average radiator temperature stays the same!

For the utmost efficiency you supply the TRV with a temperature just barely able to maintain your room temp setting. Since the amount of heat required to maintain the setting varies inversely with the outdoor temperature, supply temperature reset (outdoor reset in the case of the Vitodens) is used.

Supplied this way (with a barely adequate temperature) the main purpose of the TRV is to reduce heat--like when you're getting heat gain from the sun--or from a lot of people--or from cooking--or from a lot of incandescent light.

As long as you don't change TRV settings regularly, this "near starvation" curve will produce the highest possible efficiency with a condensing/modulating boiler because the supply temperature is always minimized.

But there's a problem if you want to RAISE temperature with any degree of speed. Why? Because the supply temperature was barely adequate to begin with. The solution is to use a supply temperature higher than required to merely maintain--it has "headroom" so it can raise heat with reasonable speed. The price of this headroom with a condensing/modulating boiler is reduced efficiency due to higher temperatures. With TRVs, the flow just reduces but the boiler STILL has to produce higher temperature--this reduces efficiency even though it's still producing the same amount of heat!

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

For your system:

Install panels (even cast iron radiators if you want to go "retro") on your 2nd floor. Use TRVs on ALL. Follow System Layout 3. The panel circuit will have its' own circulator. Size the panels similar to my recommendation of 160° average panel temperature at your Manual-J based MAXIMUM heat loss based on the design conditions for your area and whatever you consider "normal" room temperature.

Adjust the curve of heating circuit "A" to JUST maintain your MINIMUM acceptable room temperature. Considering the general overstatement of Manual-J, I'm willing to bet that your supply will NEVER need to be 160° saving extended periods of extreme cold well below the outside design temperature (and such happens only RARELY!--that's why it's called "design temperature").

This curve will define the efficiency of the boiler as it will be your "high temp" circuit. "High temp" here is relative. Relative to what? Your underfloor circuit which will need even lower temperature! Again, sized similar to my suggested and with the heat curve adjusted as mentioned, the supply temperature will NOT be very high except in the most extreme weather!

Then install your underfloor heating circuit via your mixing valve. Adjust the curve heating circuit B to again barely maintain your MINIMUM acceptable room temperature. This curve will be "flatter" and lower (less shift) than the heating circuit A.

Adjusted this way, you will have the highest possible efficiency and the lowest possible fuel consumption. Use VERY LITTLE (if any) daily setback! (This does presume you have at least reasonable insulation and infiltration control but it doesn't require "super insulation" or exceptionally tight construction.)

If you notice, I keep re-stating "MINIMUM acceptable room temperature". This does NOT mean a DEEPLY SET-BACK TEMPERATURE similar to what you're probably using now!!!! Depending on personal taste, I'd say somewhere in the low- to mid-60s.

You can even get quite "fancy" establishing your MINIMUM acceptable room temperature. If everyone is typically gone during weekdays but home on weekends, you can use the 7-day timer to your advantage. Have the boiler operate at the moon dial setting during the week and at a higher sun dial setting during the weekend--this gives you two different "MINIMUM acceptable room temperatures"!!!

What I've effectively described here is the "German way". Yes, I know they often use daily setback of supply temperature but this is NOT the same as setback of room temp! Considering their typical construction (solid masonary with exterior insulation), what they really get is the feeling of heat when the boiler is operating at the sun dial setting...

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

Now to "Americanize":

The Vitodens isn't designed to "turn on" the Unico. In fact, it's not designed to turn on anything! Its' purpose is provide the heat being lost by the system--it does this by varying its firing level to achieve the desired target. It has ZERO idea what's connected to it and it doesn't even need to know! It only needs to know how to provide the heat being lost--a job that it does with admirable accuracy.

Your so-called "high-temp" circuit supplying the TRVd panels will be WAY too low to operate the Unico in most conditions! If it is high enough then I'd be willing to bet that the boiler is operating at quite high output already and there won't be enough remaining capacity to operate the Unico unless you somehow manage to supply ONLY the Unico with heat!

You MUST remember though that the house is NOT COLD! It's ALREADY being maintained at your MINIMUM acceptable temperature!

All you have to do is "top off" the air temperature--say during the morning rush and perhaps once in the evening around the time you sit down and relax for dinner. Perhaps twice if the kids are home early and they complain that it's too cold... Here, you'll use an electronic "setback" thermostat to control the Unico, but ONLY FOR SHORT PERIODS OF TIME! While you're away during the day and sleeping at night, the thermostat controlling the Unico should be set low enough that it will NEVER turn on. If you've gotten fancy with your weekday vs. weekend MINIMUM acceptable room temps, the Unico thermostat setpoint will also be low enough on the weekends that it will NEVER turn on unless you intentionally raise the thermostat.

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Again, the Vitodens cannot "control" the Unico, but if you size, pipe and operate the system similar to the way I have described, you can use the Unico to control the Vitodens!

How?

Via the "external demand for heat" function. Don't forget that the Unico fan will be operating at a SINGLE SPEED! This means that the temperature of the air it produces is nearly a pure function of the supply temperature provided by the boiler. In other words, ther cooler the water, the cooler the air blowing from the Unico.

This is where the FIXED supply temperature produced during an "external demand for heat" can be used to your advantage. You will adjust the temperature during the external demand such that:

1) The air from the Unico is at least acceptably warm.

AND

2) The air from the Unico is warm enough to raise the room air temperature with the desired speed.

You will pipe the Unico (with its' own circulator) as the first circuit after the LLH. This gives the Unico access to the FULL supply temperature produced by the external call.

The control wiring for the Unico will still be the same as suggested at the beginning of this terribly long post... The only thing you have to do is provide a DRY contact closure to the Vitodens to initiate the external call for heat whenever the Unico is running.

What happens when the supply temp goes high during the Unico call, you ask?

1) The boiler will initially ZOOM to full fire to produce the MUCH HIGHER target.

2) The TRVs on the panels will simply reduce their flow to MAINTAIN the same average temperature of the panels! The panels will STILL be producing nearly the same heat output.

3) The underfloor circuit operating after the three-way valve can be handled different ways by the boiler depending on how you code address 0C5. MANY options! You can shut down the underfloor altogether. You can have the mixing valve continue to produce the curve of heating circuit B. (There are other options, but these are the only two I would consider.)

DO NOT FORGET THAT MODULATION IS INHERENT TO THE OPERATION OF THE VITODENS!!! Even during this "external call for heat" with its' fixed target, the burner will STILL modulate! While it will zoom to full fire, it will STILL modulate down to supply the Unico load!!!

If the load required to satisfy the Unico is greater than the difference between that required to MAINTAIN heating circuits A and B and full output, then the boiler will not be able to achieve target. Should this condition occur and the air from the Unico is objectionably cool, I would shut down heating circuit B during the Unico call.

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Sorry if I'm repeating myself Howie. I just keep adding more and more detail. If you think me single-minded, you are correct. There are other options, but they would all betray my philosophy and I do my utmost to maintain a consistent philosophy both at "The Wall" and in my work.

Mike T., Swampeast MO · March 2006

Please don't take this wrong, but you may be getting in over your head unless you do a LOT more study. I'm mainly a homeowner/DIYer myself so have ZERO problems with such, but I've dedicated an enormous amount of time, research, observation, measurement and thinking over years of time.

Yes, it's certainly possible to size your panels such that they have the same design temperature requirement as the underfloor. BUT, it's nearly impossible for them to operate with the best efficiency under the exact same heating curve. You already have the [expensive] mixing valve and controller--use them! That way you get two different curves for your two grossly different types of heat transfer. You already have the [expensive] means to get a relatively quick boost in air temp--the Unico--use it for just that purpose!

GREAT that you're thinking "vertical panels". Put them in view of outside walls/windows! You'll maximize radiation while minimizing convection! Just like the heated floors on the lower level this allows for higher comfort at lower air temperature settings.

Have you checked "Find a Contractor" here? I bet in your area that you'll find some exceptional people. You'll certainly have to pay well for their expertise, but someone will likely work with you to contain costs via your DIY.

Go to www.hvac-calc.com and buy the "one use" heat loss program. EXTREMELY easy to use! Don't use "guesstimates"--MEASURE ACCURATELY!!! GIGO after all...

Do the job well and this alone will both save you some $$ and, more importantly, demonstrate your abilities to a good contractor.

Dave_4 · March 2006

Excellent... excellent post

Thanks!

It's a pleasure to talk with someone who knows the Vitodens as well as you do. Reading the manuals carefully is one thing, but you are confirming all of what I've read and thought I understood, which makes me happy.

Are the radiators piped in parallel off a manifold in the boiler loop?

My last question is the same as nrtRob's. Why not (over)size the radiators for the same maximum temperature as the floors. Would they be too large, or not function properly?

Oh wait, not my last question... recommendations on brands of radiator?

Thanks again,

Howie

Dave_4 · March 2006

You beat me to it....

we're crossing posts now.

What do you mean by "in view of an outside wall"? I take it you mean "don't put it on an outside wall".

I've been working with NRT... they put the design together for me, but the installation so far has been all me (and I'm sure will continue to be), except for the gas.

Howie

Mike T., Swampeast MO · March 2006

On interior walls where the panels "see" the outside walls and windows.

Vertically oriented panels are IDEAL for such an installation. At least twice as tall as they are wide.

Search here or on the web, and you'll find a scientific (European) study of such panels. Proportional control (e.g. TRVs) are ASSUMED as ONLY proportional control will guarantee that the heat loss of the space is being maintained via the lowest possible average panel temperature and, consequently, the highest possible potential for radiant heat transfer. The vertical orientation retards convection--putting the panel in view of the exterior surfaces (which "want" to be the coldest) further enhances radiation.

At least reasonable insulation/infiltration control are REQUIRED for such installation. Otherwise cold air will "pool" at the floor and the low level of convection will lead to "cold foot syndrome".

Dave_4 · March 2006

pipe size?

The house is well-insulated... 6" framing with blown, dense, cellulose. There is minor infiltration where the windows close, but without that the house wouldn't breathe all that well.

Since you guys have told me I need to repipe the boiler ciruit to 1", I assume this means running 1" pex to the radiators?

Mike T., Swampeast MO · March 2006

Thank you!

Excuse my arrogance but I understood the Vitodens before it existed!

You have two options for piping the panels. "Home run" to manifolds or traditional two-pipe mains with individual branches to each radiator. TRVs negate the need for reverse return when using traditional mains. Use reverse return with manifolds--not because they're really needed but because it's just standard (good) practice.

Sorry, but I can't help with brands of panels. I've never used such and have only felt them in London. My familiarity is standing iron radiators.

If you go "retro" either use two-column or tube-type radiators. I'll still insist that US Capitol tube radiators with their bell curve design are exceptional at dispersing general radiant energy while at the same time giving focused lines of concentrated energy.

Dave_4 · March 2006

home run?

If I use manifolds, I'll either have to add a bypass directly between the manifolds, or on each radiator? I have to guarantee flow since this is the boiler circuit, yes?

Mike T., Swampeast MO · March 2006

You can size the panels to operate at ANY temperature you want. BUT, they can get awfully big and expensive if you go really low.

The sizing recommendation I have (160F average panel temp at Manual-J design) was carefully chosen. Not only from my own experience with cast iron raditors, but from the experiences reported here using modern panel radiators with the Vitodens.

Sized this way I seriously doubt that your SUPPLY temperature (let alone the average radiator temperature) will approach 160F in any but extended periods of weather WELL below design temp.

Manual-J already has significant "fudge factor". When you're using proportional control this only means that emitters will operate at temperatures significantly lower than you expect. Trust me--you can go too low. When that happens you loose your apparent source of heat unless the weather is quite cold!

Mike T., Swampeast MO · March 2006

In this case you won't need a differential pressure bypass.

Why?

The low-loss header IS your bypass.

Mike T., Swampeast MO · March 2006

Absolutely not! You will size the branches to the radiators based on their proportion of system requirement while still ensuring that the residual of the built-in circulator is not exceeded.

Search here for one of my series of posts regarding sizing a TRVd system with a variable-speed circulator. If you absolutely can't find, let me know and I'll post the link.

Mike T., Swampeast MO · March 2006

Just my best guess for a balance of efficiency with economy of installation. See other posts (not just in this thread and not just by me).

Mike T., Swampeast MO · March 2006

BAD MISTAKE ON MY PART!!!

Please read!!!

That's a flat plate heat exchanger in System Layout 5--NOT A LOW-LOSS HEADER!!!! ARGGH! Sorry, sorry, sorry!!!! I feel like a complete fool! Was trying to figure out why there was a 2nd expansion tank then saw my absolutely stupid error!!!

You'd use something similar to System Layout 3 where EVERYTHING is isolated via the LLH.

I will however still highly recommend TRVs on your panel circuit. You'll still be able to use the "external call" to power the Unico. The TRVs will still throttle down. You'll still be able to either maintain heating circuit B's curve for the underfloor or shut it down completely when the Unico calls. Only real diference is that the panel circuit isn't directly connected.

While you could use individual zone valves and wall thermostats for the panels, you'd loose the regulation ability of the TRVs. When thermostat(s) call while the Unico is running, the panels will "rob" much of the heat that you want to go to the Unico. The panels will heat rapidly--but they'd overheat in most weather and the Unico air could well go cool. If you utterly insist upon zone valves and wall thermostats for the panels, you'd need a second mixing valve and controller for the panel circuit, similar to Layout 4. I believe you'll find that the TRVs will cost less than just the Dekamatic HK-1 required to operate that 2nd mixing valve--not to mention the zone valves & thermostats.

(I'm going to edit previous posts so eventually this correction won't be needed.)

Dave_4 · March 2006

Oh no! I just finished installing it!!!

Just kidding. Glad you caught the error :-)

So you convinced me not to go with zone valves on the radiators. I think the change implies I want to have separate pumps for the radiator circuit and the Unico. However there's a problem with that...

If I have separate pumps, I can slave the radiator pump to HCA at plug 20, and the Unico pump to a call for heat from the thermostat. But then I lose the freeze protection on the Unico pump, which is really where I need it. If I keep one pump, then the Unico will rob BTUs from the radiators just by being part of the circuit.

This wouldn't be a problem with zone valves, because then I'd have the radiators and the Unico on the same pump. The Unico would still rob BTUs, but only when the radiators called for heat.

So given those choices what do you think? Unico robs BTUs all the time (and I get freeze protection) or some of the time (and I have to rig up something else for freeze protection). It *is* likely that we'll insulate the attic within 5 years.

A second mixing valve accessory (I hear) is big bucks. I don't want to go that route.

On a related topic, I was looking through my latest acquisition (the mixing valve kit and expansion board). It seems like the expansion board is uncessary? I don't get a "plug 20" out of that. Do I need the expansion board *and* a power/pump kit/board? Do you know the part number for that? Oh wait... I just checked the part numbers. Looks like I got the one for the WB44 and up, which doesn't control a pump. I wondered why the picture in the instructions showed some stuff in the boiler that I don't have. I guess if I get the correct expansion board, I should have a "plug 20".

Paul Pollets · March 2006

3/4 x 1\" increasers

We increase the piping directly under the boiler as the first fitting.

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

Nick S · March 2006

Freeze protection

You could use an aquastat strapped to the piping near the Unico. Set it to turn the pump on at a pipe temperature of 40 degrees or so to provide freeze protection. Set the differential as high as it goes to keep the pump from short cycling. Why waste energy heating the Unico when all you need is to keep the water above freezing.
Nick

Dave_4 · March 2006

Thanks for all the fish...

First, I would like to thank everyone who responded, especially Mike. I wanted to let you know what I decided to do, much of it based on the good advice of Mike and the other folks on this board.

Im planning to use two SR501 relays and an SR504 to ensure that whenever the Unico fan is running, the heating circuit pump is running to provide more comfortable air. If there is DHW production *and* a call for heat, the fan will not run. If there is no call for heat (just fan-on), the fan and the heating circuit pump will run. In this situation there may not be heated water if there is DHW production, but since theres no call for heat, it doesnt matter that much. If the fan runs long enough with unheated water to trigger a call for heat during DHW production, the fan will turn off. What I want is a hands-off system that does the right thing, and I think this will do it. I also have a third SR501 to ensure that the fan does what its supposed to do when the thermostat is switched from Heat to Cool.

As for freeze protection, the only way to achieve that independent of the Vitodens is to put the Unico on a separate heating circuit from the radiators, i.e. add a pump, a relay, and an outdoor sensor for freeze protection. This doesnt seem to make much sense to me, since I already have the outdoor sensor and freeze protection logic of the Vitodens, albeit at the expense of running hot water through the Unico coils even when there is no call for heat from the Unico. Overall probably a small price to pay until the attic is insulated. The heating coil does have some insulation out of the box.

The HCB curve will be set for the radiant floors, and the HCA curve will be set for the radiators. The Unico thermostat call for heat will trigger an External Changeover of Heating Program to 180 degrees.

The Vitodens with control the radiator/unico pump for HCA via the expansion board (209) for my WB6-24.

The only thing left to verify is that the mixing valve will close as necessary during the external changeover of heating program.

Thanks Ill provide more pictures when Im done.

Howie

Vitodens / Unico configuration

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