The introduction to Viessmann - Service trip to a Hybrid System in Boston MA. It was reported, often, that the Weishaupt burner was locking out. Each service trip was unsuccessful in finding the actual cause of the ongoing, periodic lockouts. Thinking outside the box, it was decided to put a touch of paint on the burner control reset button to test whether or not someone was actually pushing the reset button.
As suspected, the button was being pushed, but by whom? A camera was then set up and revealed that a tenant was entering the boiler room and pressing the reset button, causing the burner to lock out.
The moral of the story, not all service calls are due to defective equipment.
The Viessmann installation included a commercial condensing boiler (Vertomat - VSB) and a gas-fired atmospheric boiler (Atola RN). The two boilers are being controlled by Dekamatik M1 (VSB) and M2 (Atola) controls.
This type of system, where two different style boilers are installed, is often considered a “hybrid” system. The Vertomat is a Stainless Steel (316-Ti) boiler and the Atola RN is a cast iron sectional boiler. The Vertomat can handle the effects of the aggressive condensate it is designed to produce the heating output of the gaseous fuel being used. The Atola is not designed to condense therefore the water temperatures it is designed to operate at are considerably higher than the Vertomat.
Boiler limitations:
Vertomat
- Maximum Fixed high limit 210*F (99*C)
- Designed for low to medium-temperature applications
- Price
Atola RN
- Requires a minimum operating temperature to avoid condensation buildup within the flue passages which will corrosion and heat exchanger failure
- Efficiency
In hybrid applications, the use of condensing and non-condensing boilers in the same system was due to a few factors, one being the cost of installation, and another being system temperature requirements. As noted above, each boiler has unique limitations.
The Vertomat was an expensive boiler to purchase, but in time paid for itself due to the energy savings available from the use of outdoor reset and the ability to condense, which would extract an additional few percentage points of efficiency. The savings achieved during the shoulder heating periods, fall and spring, where system temperatures could be below 100*F and still satisfy the heating requirements of a building were enough to make the price of the boiler worth the investment.
Note: the model number of Viessmann boilers in the early days was based on the boiler heating output, in KW (kilowatts). Conversion: 1 kWh is equal to 3,412 BTUH.
Gas-fired condensing boiler with Weishaupt burner operating with either Natural Gas or Liquid Petroleum Gas (aka LP, LPG). The original VSB boiler had sizes from 190 MBH to 3361 MBH.
VSB-05 to VSB-13 were single vessels.
VSB-17 to VSB-89 were two vessels that were put together with a silicone-type sealant between the front section (aka Nose Cone) and the main vessel. The water passed from the main vessel to the front section via a flanged connection at the bottom (Return) and top (Supply).
These models also had two return connections (upper and lower) in order to separate high-temperature return from the low temperature return in a system that had low temp radiant and high temp circuits or DHW.