Viessmann: The Principles of Comfort and Savings
Weather-Responsive Controls and Low Temperature Boilers
Once all this data is factored in, a total heat loss is calculated in British thermal units per hour (Btuh). As an example, let's assume that a 3,800 square foot house has a heat loss of 150,000 btuh. That means that on the coldest night of the year, with a temperature outside of either zero or minus ten degrees, you will need a boiler that will produce 150,000 btuh at 180 degree boiler water to make up for the heat that leaks out of your home.
Simple enough right? Not necessarily. Consider what happens on all the other nights that are not the coldest night. The average outdoor temperature through the entire heating season is 48 degrees F. When you turn up your thermostat on one of these average days, that 150,000 btuh boiler kicks on and starts pumping 180 degree water around. Two minutes later, just as you feel that first wave of heat rolling toward you, the boiler shuts off. Because the boiler is sized for the worst case day (and then some) it is way too big for the building at 48 degrees outside. It heats up much faster than the baseboard or radiators can distribute the heat to the house. This causes 'short-cycling' which wastes fuel and leads to unnecessary wear and tear on the heating plant. Rooms can overheat and radiators and baseboard can make strange ticking or moaning noises. It is not the best situation.
As you can see from the chart below, the vast majority of our heating hours have temperatures well above freezing. The design conditions occur less than .3 percent of the heating season (approximately 20 hours out of 7,300). This chart is based on actual weather data over the last 65 years and reminds us that the vast majority of our heating hours are at temperatures well above what your boiler was sized for.
Now everyone wants a boiler that can heat up the house fast. Right? Not really. If fuel were free and people didn't mind large temperature swings every time the thermostat came on it would be OK. But fuel is more and more expensive and people are always more comfortable with an even temperature. The problem is that your boiler is actually too big for your house 99.7% of the time. The warmer it is outdoors, the more oversized your boiler becomes. Like a car with a way too big engine, an oversized boiler waster a lot of fuel dollars. If you are interested in saving a sizable portion of your heating budget every year and be more comfortable, there is a solution to this problem.
Outdoor Reset Controls
An outdoor reset control essentially adjusts the size of your boiler to match the necessary heating output based on outside temperature. It doesn't physically change the boiler size of course. It does adjust the boiler's output by changing the boiler's water temperature. The direct relation between the outdoor temperature and how hot your boiler needs to be is illustrated below.
Weather responsive controls (reset controls) are an electronic energy management system that uses a tiny computer chip to balance boiler water temperature with outdoor temperature. By constantly measuring outside temperature they determine the optimum temperature needed to heat your home. It is a brilliant yet simple control strategy. These controls have a sensor on the North side of your home and a sensor mounted at the boiler to sense water temperature. Some use a third internal room sensor to provide additional information to the control. This room sensor can detect inside heat gains from solar, fireplaces, cooking or people or extreme heat losses from wind chill.
The benefits of reset controls are many:
One factor is energy savings. For every three degrees that the building's water temperature can be lowered, there is a 1% fuel reduction. If the system was firing at 180 degrees and now is averaging 130 degree water, the savings will be at least 15% (180 130=50 divided by 3 = 16% savings).
Another factor is comfort. Because the output of the radiators or baseboard is now precisely matched to your home's heat loss, there is always just enough heat being radiated to keep your house warm. You keep up with heat loss, versus trying to catch up. Radiators don't get hot and then cold, they always give off just the right amount of heat. Weather responsive controls leads to long on cycles and long off cycles on the boiler. This provides constant room temperature, extremely quiet operation and reduced water and tear on the heating system components.
Another factor is equipment stress. Without reset controls your radiation cycles on and off constantly. Just as your baseboard has cooled down, the boiler kicks on and pumps scalding hot water back through it. This can cause ticking or banging as everything expands from sudden temperature change. These 'on and offs' are rough on every part of the system: boiler sections, pumps, burner, motors and piping. Imagine a car that did not have a gas pedal but only had an on switch and a brake. You would constantly have to switch from full speed to brakes to achieve a safe speed. Imagine what that would do to your car and its efficiency and you can see the stress that a high temperature on/off system endures.
Viessmann Boilers and Reset
Viessmann is the only boiler on the market today fully able to utilize all of the advantages and energy savings that a reset control can provide. Most oil-fired boilers cannot operate at low water temperature. Due to their traditional design, when their water temperature is below 140 degrees F, the combustion gases actually condense on the inside of the combustion chamber. This condensation causes several serious problems. Foremost is a condition called plugging up or "blow back". The wet faces of the boiler sections attract soot from the burning oil. The longer the boiler operates the more layers of soot build up until the efficiency drops or until the sections are plugged.
The second problem is that when the flue gases condense on the inside of the standard boilers they produce sulfuric acid on the boiler sections and cause premature failure. That is why these type of boilers are factory equipped with burner controls with minimum settings of 180 degrees F. The graphic below shows how much of the heating season demands a boiler that will operate at water temperatures below 140 degrees to achieve the highest heating efficiencies. In over 97% of the heating season, standard boilers are simply not able to utilize even a small part of the advantage provided by an outdoor reset control.
The Viessmann Advantage
The Viessmann Vitola biferral is very different. Its unique (and internationally patented) design allows it to operate at even the extremely low temperatures that a reset control can ask for. It utilized sandwiched heating surfaces: inside cast iron outside steel. The ring shaped cast iron elements with the radial fins always maintain higher temperatures than the steel surfaces, thus effectively preventing flue gas condensation and the sooting and corrosion problems that a standard boiler is subject to. Just as a thermopane window eliminates condensation, the sandwiched heating surface provides trouble-free combustion. Another Viessmann boiler, the Atola Renox has a special return distribution tube that also allows lower temperature return water to a sectional boiler.
The Viessmann boilers also have high water content. The average capacity for the Vitola Biferral is thirty gallons. Standard boilers have average water content of eight gallons. What does it matter?
During every startup phases of a firing cycle (approximately 1 to 4 minutes) an increased amount of unburned hydrocarbons and carbon monoxide are generated. By decreasing the frequency of firing cycles, the number of poor combustion periods are reduced resulting in overall higher seasonal efficiencies and drastically reduced harmful emissions. Think about the smoke from the tail pipe of any engine when it first starts up.
By simply increasing the water content, the total number of on and off cycles is reduced from 30,000 to 10,000 which translates to a 60% cycle reduction 20,000 fewer times that the burner fires! This will also mean less frequent heating cycles, which will reduce wear and tear on control and burner components and subsequent equipment failure. By insulating the pressure vessel with 3" of high R-value insulation (versus 3/4 " for standard) the boiler standby heat loss is minimized resulting in excellent yearly efficiency.
For the home or business owner interested in achieving the highest levels of heating comfort, overall heating efficiency, rate of return on investment and lowest operating costs, Viessmann boilers are the best value. No other boiler company has taken such pains to produce what we consider to be the finest heating equipment on the market today. High efficiency heating equipment is the only purchase that can pay for itself with better equipment and peace of mind. An automobile doesn't, a vacation doesn't S only heating equipment. The heating heart of your home is an investment over 20 to 40 years...