Viessmann Vitodens 200 setup

Canecreek

I need help understanding how the best ModCon on the market operates. I have read al of the manuals and am still unclear how to call for heat with their system plans. Mt current system is a Smith cast iron oil unit that has a simple setup in that the thermastats call for heat by activating 24v relays to start the circulating pumps on 2 separate zones. Once the water is flowing the boiler fires based on the return temp across an aquastat.

Viessmann does not show a plan for 2 heating circiuts with no mixing valve. The current system pumps through the boiler with 2 B&G 100's with a B&G air separator and expansion tank just out of the boiler supply. I would prefer to pump away but the 2" supply runs about 20' before teeing off into 2 11/4" lines which will involve a lot of tear out and plumbing to change this configuration. My plan to overcome this problem as well as other issues is to install a LLH with a boiler circulator and replace the B&G's with VFD's. I can easily control the VFD's with the current relays and have pretty good control over the system by installing the Viessmann LLH sensor to control the boiler output. This plan will cut out a lot of the control I would have over night time setback and several other nice functions of this boiler. I have no need to have separate control of the 2 existing circiuts but do want to have even heat from both circiuts.



Questions



1. How does this boiler normally call for heat? Is it through the outdoor reset?

2. Will my system function ok with the system circulators on the returns or will the LLH take care of this problem? I know that this was common practice years ago in order to have the lowest heat possible across the pumps.

Total1

call for heat and outdoor reset ..

I can answer how the boiler calls for heat -  when 3 and 4 on terminal x4 close the boiler starts . I have 3 and 4 connected to my end switch on the zone valves .  So the thermostat calls for heat , zone valves get power , when they open , the end switch closes . firing the boiler and the pump start that is connected to the X3 terminal .  the outdoor reset just adjusts the boiler firing with regard to the outside temp .

  

Paul Pollets

Vitodens 200

I don't know if you're a homeowner or contractor, but the Vitodens 200 needs to be piped exactly the way the schematics show in the various examples given in the installation manual. The boiler works by sensing the outdoor temperature and the outdoor sensor is fully capable of running the system without a thermostat, providing the heat emitters have been sized correctly. If you have radiators, change the valves to TRV's while the system is drained down.

The boiler can be operated by either of 2 Vitotrol thermostats offered. Both can be configured to give feedback to the computer, if needed or desired. Conventional thermostats cannot be connected to the 200. The new models can be configured to an iPhone app.

The pump between the LLH and the boiler is usually a 15-58 Grundfos or equivalent and the system pump should be variable speed. I use the Alpha pumps. Pipe size is dependent upon required flow rate to the system. Without a heat loss, it's guessing to say the 2" main is oversized.

Your description of the existing system is from the late 1940's or 50's. Bringing the system into the 21st century requires a thorough understanding of how it works and how to pipe it correctly. If you take shortcuts, expect problems. If you do it right, it will deliver amazing efficiency.

Canecreek

Viessmann Vitodens 200

Thanks Paul,

First let me say that it is very generous of the pros on this site to be so willing to help a novice understand the vast complexity of boiler science. Thank you.

I agree with you the system should match the Viessmann layouts. I plan to combine the 2 current zones to one circiut with the system circulator exactly as it should be. I am thinking the addition of trv's with a variable speed circulator will balance the system pretty good. I will obtain the correct Viessmann separator and sensor to match the boiler and system. I am not interested in cutting corners. I would like to avoid unneeded work. That being said I am concerned about my pipe sizing.

Here is a little more back ground on the system. I have done a heat loss 2 ways. First I went through the slantf fin program and got it as close to my house as possible. I have a unique house with 2x6 walls, 1 1/4" plaster and 1" thick pine siding that is very tight (no loose or lifted boards, no cracks or air inlets). Wy windows are all single pane casements but are very tight. I have insulated curtains on all windows. The slant fin came in around 30. I have a 28,000 btu unvented gas heater I have used in the early and late heating season so I calculated my gas usage against degree days and got a heat loss of 22. I split the difference to 26. I am heating about 4200 sq ft so about 110,000 btuh should do it. I have 1800 sq ft of radiator based on 2.5' per section of 4 tube 23" tall radiators giving me a max heat load of about 60 btus per ft. I calculate that I will need a max temp of 125 - 130 deg making a good mod con a great choice. I plan a 20 delta which will require a system flow of around 11 gpm. A good variable speed system circulator should do a good job maintaining the delta. The Viessmann LLH with temp sensor will protect the boiler from the higher flow rate of the system and maintain the correct fire modulation. I may get the Viessmann remote if only to provide actual inside temp feedback to the boiler control to compensate for solar gain and wind loss but perhaps not before I see how it performs with out it.



Having said all that my concern now is about your comment that my pipe may be over sized. I am a professional and when I am unsure of my knowledge I look for other pros who can straighten me out. I look forward to hearing about where I screwed this up so I can revise my plan.



Thanks again for your generous help.

Tom

Paul Pollets

Pipe size

I'd connect to the system side of the LLH with 11/4" pipe with 11/4 circ flanges on Alpha pump. You could use 1" piping if you're confident of correct flow rates. If you do the TRV's, system balancing will be very easy. Place any Vitotrol thermostat in the ambient area. If the Vitotrol sensor is enabled and the room has a radiator with a TRV, the TRV must be left at "5" or fully open, or the thermostat will not respond accurately, nor will boiler water temps be as low as they could be.

SWEI

Boiler sizing

That heat loss is lower than the maximum capacity of the smallest mod/con boilers currently available.  The important figure to consider in this case is the boiler's MINIMUM modulation rate.  The new B2HA 19 has one of the lowest (12,000 BTU/hr.)

Canecreek

Boiler sizing

Did I do my math wrong? I got heat load of 109,000 btuh

Canecreek

Pipe size

Most of the system pipe is 1 1/4" the supply is 2" for about 20' then reduces after the tee. The return expands to 2" after the tee. Altogether about 25' of 2" that will be reduced to about 18' by relocating the boiler. Will the flow be adversely affected to reduce the supply and return to the same size as the branch piping?



Tom

SWEI

My sincere apologies

I read 28k there!  B2HA 35 will do the job with aplomb.

Canecreek

Boiler sizing

I thought that was what you had seen. No offense taken I assure you. I am very greatful for your willingness to share your knowledge with me. Any thoughts on my pipe size issue?

SWEI

Pipe sizing

If you run the radiators at a 30ºF ∆T, you would need to move 7.3 GPM through your secondary (distribution) loop.  1" Type L copper will handle that easily (7.5 GPM at a velocity of 3 FPS.)  At 9.0 GPM you would be pushing 3.5 FPS with a 24ºF ∆T (on the coldest day of the year.)



Taco Bumble Bee?

Canecreek

Pipe sizing

My existing system has a 2" supply and return which branch to 1 1/4". No zones just 2 branches on a 1 pipe system with diverting tees.