Viessmann RS/WS Option

Perry_2

If you do anything - get the RS, and not the WS. The RS is the one that can feedback room temperature. I use one on a Cast Iron baseboard application and it works well. What it does is shift which curve is being used - up to a point. It will also shut the boiler down if things are really getting to warm.

If you have a radiant floor heat system. An RS can be tied to the zone mixing valve - and then it only controls that zone and not the entire boiler (wiring/system diagrams are in the literature).

Perry

rumn8r

The Vitodens has been purring along nicely now for several months without any indoor feedback. Tweaking the heating curves has resulted in excellent temperature maintenance for day and night setback except for 3-4 degree overshoot due to solar gain on bright clear days.

The question I have is - if I add in the RS or WS stat what - exactly - happens to the weather responsive part of the built in boiler control. Does the curve shift, does the offset temp adjust, is it ignored entirely?

Can anybody from Viessmann (or a Viessmann fanatic) jump in and explain what I should expect to happen if I add that option?

The system is a combination of standing iron with TRVs, underfloor, and infloor. A Taco RMB and manual mixing valves handle the cooler zones. Obviously with the Taco RMB in the mix all I could hope to accomplish for those zones is to starve the RMB for inlet temp on sunny days.

Thanks to anyone who can explain the inner control logic of this wondeful machine.

ALH_4

parallel shift

The WS/RS put a parallel shift on the heating curve. Whether this would eliminate your overshoot depends on the mass of your system. It sounds as if you are medium to high mass, and Viessmann does not recommend indoor feedback with this type of system.

It sounds as if you have your system well dialed in, and things are working pretty well. The TRV's are already giving you some indoor feedback. I'm not familiar with the details of the RMB, but depending on what type of radiant floors you have and the mass of each, indoor feedback might not make much difference.

I would say your system is working very well.

-andrew

rumn8r

Thank You

Thank you for the response Andrew. I'll have to find out what it costs but it might be worth it to me to give it a shot just to see if I can correct the overshoot on those days.

Scott

jp_2

over shoot?

Is the entire house overshooting or just a couple rooms, like the southern exposed room?

on second thought: certain conditions can't be controlled. as in my cabin, solar gain can solely heat the place, inside temps go from 45F to 70F on a sunny 20F day. so sometimes the only way to control over shoot is to open windows or cool the room. the boiler can't control these situations. temp controlled window shades would work.

embrace solar gain! Its free heat!

ALH_4

In this case

The Taco RMB is controlling the zones that do not currently have indoor feedback (TRV's). Viessmann does not recommend the RS on high mass systems such as concrete pours. Given that the Viessmann motorized 3-way was not used to control the reduced temperature radiant floor zones, I do not see how either the RS or WS will affect the temperature in any of the zones.

If the Viessmann 3-way was used, the WS would be more appropriate than the RS for those areas with high mass radiant floors. With Thermofin radiant floors, or equivalent, the RS could be used in my opinion. In this case, the RMB really negates any effect indoor feedback to the boiler would have. I do not know if there is an indoor feedback option on the RMB.

See page 33 of the TDM Vitodens 200 24/32 Technical Data Manual

Also, if the Comfortrol display is remote-mounted, it can be used for either WS or RS operation. I am not a big fan of this method, because it makes service more difficult.

-Andrew

EDIT: For some reason I have been thinking it is the radiant floor zones that overshoot, but that may not be the case. If the radiator zones are the ones that overheat the RS may help or may not since TRV's are already used. The price of the RS is just a bit more than a good thermostat if I remember correctly.

Mike T., Swampeast MO

Is the 3-4 degree overshoot throughout the house as a whole? or only in the non-TRVd areas? or only in a "sun space"?

Ron Gillen

Anyone know why the RS can't be hooked to the heating circuit without mixing valve? I posted a picture of my system a while ago. ICF home, all radiant, Staple up with plates for main floor of walk out bungalow. Southern exposure. 70 degrees up and down. Upstairs can go to 75 on a sunny day and I wondered if the RS would help. Just using outdoor now.

rumn8r

Thanks to all for your input

To clarify further: The situation is a bit unique currently as the house is wide open internally - 4 floors no doors and large open rooms. Outside walls are 20% glazing on average with no window coverings currently. I'm llocated in south central Wisconsin.

The basement has the in-slab, the kitchen on the first floor and the bathrooms on the 2nd floor have the underfloor. 8 of the 12 radiators have local TRV's installed. I have yet to get around to installing the RA2000 valves with motor operators at the basement manifolds for the other 4. I went that route with those 4 because my wife would like window seats over them someday and I didn't want the capillary tube running up the wall to a remote sensor.

The in-floor and under-floor all runs off the RMB and each has it's own ESBE manual mixing valve. The intent is to try it manually for a while and if the temperature regulation isn't adequate then add the motor operators to those as well.

So - all that said this may be a "temporary" problem. But my temporary problems often turn into long term problems given the pace of my work so I thought maybe the RS option would help in the menatime and also prevent hotter-than-needed boiler temps on those sunny days.

Because of the open design of the house and the fact that even in places where there will eventually be doors there are none now the temperature differences between rooms aren't even noticeable - except between the basement and upper floors.

I appreciate the feedback greatly. I've got an email in to our "local" Viessmann fellow and am waiting for him to get back to me with a price for the RS option.

I don't believe the RMB has any provisions for indoor feedback but if someone knows otehrwise I'd love to know.

Thanks again,

Scott

Perry_2

The problem is system response time

A high mass system - such as radiant with it huge amount of tubeing and the water in it, and the mass of the floor, responds to slowly for the RS to be effective if applied to a very large area. The results would be quite noticable overshoots.

It does work on individual zones.

It is a perfect match for baseboard or other radiator heating systems that have a lot less water volumn than radiant heat.

Perry

jp_2

look before you leap!

I strongly suggest, before you add more controls, make sure you know exactly why your problem exists.

suppliers are happy to sell controls, the suns going to heat up spaces no matter what control is on the boiler!

read my post again, 45F to 70F on a sunny winter day, no other heat source. the sun has a lot of power and I'm probably 200 miles north of you.

edit: Ok, you may not be able to stop the rise in temp but i suppose you can stop the boiler from sending heat to that area.

Simply Rad_2

On the Contrary

I have had good luck with the RS control and remote mounting the comfortol with indoor feed back with high mass systems. One system in particular has suspended floor with 4" of pured concrete on 2 levels the system is within one degree of the set point all the time. I know Viessmann say not to do this because of inersia but I can say that is does not hurt to try. Here is what I have been doing. I mount the comfortrol in the great room(largest heat loss area) using it for indoor feedback and continuos circ-no control valve just indoor feed back. Then the rest of the zones use either TRV sytel control for zzone actuators. I have been using Oventrop non electric valves for flow modualation on the radiant floors and the system works great. I'd say try. I do cover my butt and install a control wire or conduit for the constant cir zone if the system does not work then I can set it up with a zone control.

Here is a picture of my last system.
Good luck Jeffrey

ALH_4

mass

When you say staple-up with plates, do you mean extruded aluminum plates? If so, I consider this installation method to be very responsive, and in my opinion the RS is a good match for this type of floor. The mass is relatively low, and the response time is short, two of Viessmann's criteria for effective use of the RS.

-Andrew

Ron Gillen

Plates

I have Wirsbo extruded plates and all oak or tile flooring. The manual says "the remote control will be assigned to the mixing valve circuit". How would you assign it to the high temp circuit? I assume it would need to be wired differently or is there something in the programing that I haven't found?

ALH_4

high/low

If you do not have a mixing valve, the RS shifts the boiler heating curve.

If you have the mixing valve, the RS can only provide feedback to the low temperature circuit. I think this is because using indoor feedback on the boiler circuit could potentially starve the mixing valve circuit of water warm enough to heat those zones, and Viessmann has provided for only one indoor sensor.

Mixing valves can also be controlled by the Dekamatik HK-1 which has the option of indoor temperature feedback. Tekmar zone controls could also be used though there is no interface between the Tekmar controls and the Vitodens.

-Andrew

Ron Gillen

Thanks Andrew

I don't think starving the basement circuit would be a problem. If I'm understanding this correctly, the only way to control upstairs is by moving the comfortrol which I don't want to do. I have heatlink headers, perhaps i'll add zone valves as high limits in the two warmest rooms.

Eric_6

Sweet piping job Jeffrey. Hey, you were suppose to be out working at 9:41 a.m. Have you started the Viessmann solar install yet ?

Best Regards,

Eric

Mike T., Swampeast MO

Almost sounds like the four rads without TRVs are "stacked"--one on each floor (perhaps in a bay)?

If so, I have a feeling that most of the problem will disappear when the TRVs are added to these rads. Only 4°F of overshoot on very sunny days with 1/3 of the radiators without TRVs makes me believe that you've adjusted the boiler curve VERY well.

Viessmann literature doesn't seem to say much about how the RS affects the boiler curve. The main thing I see about the RS is that it isn't generally recommended for higher mass/volume systems. The troubleshooting information in the Start-up/Service Instructions gives a clue:

Remember--both the WS and RS have "sun" and "moon" settings, just like the Comfortrol™. Above about 64°F the resistance value of the "sun" setting increases faster than the "moon" setting. I suspect that the boiler uses this to produce a supply curve boost in certain conditions. Say the current room temp is 65°F with "sun" setting on the RS also 65°--you then raise the "sun" setting to 70°. The boiler target will be then be equivalent to about a 75° "moon" setting. Once the indoor temp approaches the "sun" setting, the target may well shift down to the "normal" level.

Unfortunately, I have no idea how it handles overshoot. I suspect however that it merely shifts the reset curve down by the amount of overshoot--e.g. if room temp is 4°F above the "sun" setting, the curve will shift as if the outdoor temperature had risen 4°F. Note no "extra" shift as appears to happen if there is an undershoot!

In your sytem that will mean that the supply temperature available to EVERYTHING will be reduced similarly.


Your boiler curve already seems nearly ideal such that the non-TRVd rads only need the TRVs to compensate for solar and occupation gains--otherwise the curve is essentially perfect. Reduce the curve for the ENTIRE SYSTEM during overshoot and you might upset what sounds to be an ideal curve.

TRVs on the remaining rads is likely the best solution. I would consider the RS in the interem if the TRVd rads all or nearly all go CONSIDERABLY cooler than the non-TRVd rads during periods of high solar gain. If most of the TRVd rads are just a bit cooler than the non-TRVd, the WS might throw off the balance that you've already achieved by effectively starving the rest of the system for the sake of four rads that only slightly overheat. This sets up a viscious cycle whereby the boiler has to ramp up and down with greater magnitude than the load. The Vitodens certainly is a "wonderful machine", and it appears to be most wonderful when providing heat at just the rate it is being lost.