Boiler Efficiency Options - High Performance HVAC wants to help you understand your next boiler purchase better. To do this we want to break down all the different types of boilers and components, and various options and features that you may find when making a purchase.
Typically, you want to find a like replacement for the boiler you currently have installed, or if you are buying a new boiler, you want a system that will handle the load and is durable. The most important feature of the new purchase is usually the fuel efficiency simply because the cost of running the new system will give you pay back over time for the new purchase.
Boiler Efficiency Options - Automatic Flue Dampers
There are usually options you can get with a boiler that will make it more efficient for example…..an automatic flue damper. The automatic flue damper will automatically open up when the boiler fires and automatically close when the burners shut off. This automatic flue damper holds heat inside. Without an automatic vent damper, the heat will rise up the flue contributing greatly to heat loss during the off-cycle of the system.
Since the system usually cycles based on the temperature inside the boiler heat exchanger the longer you can keep the heat inside the heat exchanger the least the burners will cycle to heat the heat exchanger up to the aquastat setting temperature.
The boiler aquastat controls the boiler burners and typically the circulator pump for the zone or zones in the piping system. Note that an automatic vent damper does not apply to condensing gas or oil boilers as the condensing gas or oil boiler utilizes the maximum amount of heat that the boiler produces. The flue pipe for condensing gas or oil boilers is typically PVC pipe but the heat loss experienced with a condensing gas or oil boiler is usually very minimal to nil through the flue pipe.
Boiler Efficiency Options - Outside Ambient Temperature Reset Control
A boiler reset control is a device that will adjust the upper limit set point on the boiler as the outside air temperature changes. If it is colder outside, the boiler will operate at temperatures to 100% of design limits based on the reset temperature control for a boiler. When the temperatures are milder or warmer outside this set point on the boiler will be lowered automatically by the boiler reset controller.
Changing the set point on the outside air temperature will help you save energy when the weather is not so cold outside and continue to keep you comfortable even on the coldest nights by raising the temperature the boilers operate at for a water temperature set point.
Typically, outside air temperature boiler resets are sold as an optional component. High Performance HVAC recommends to consumers who purchase boilers that they have the installation contractor install an outside air temperature reset controller.
It will cost you an additional fee, and sometimes this can be negotiated when you are negotiating for the boiler installation costs. A few boiler manufacturers automatically provide outside air temperature reset controllers with their boilers so make sure you ask about this feature.
Boiler Efficiency Options - Condensing Boilers
When deciding to purchase a boiler, you should consider a condensing boiler as these boilers are the most efficient boilers you can buy. Efficiency is especially true in modern times with the high cost of fuels for heating systems. Getting the most out of the fuel you purchase is important, and condensing boilers offer higher efficiency ratings than the typical boilers. Give extra attention to condensing boilers over conventional boilers when making a boiler purchase.
A condensing boiler has two heat exchangers. The primary heat exchanger absorbs the bulk of the heat from the combustion process while the secondary heat exchanger removes more heat from the combustion gases before they are vented up the flue. In most situations, the amount of heat removal by the two heat exchangers is so great the excess flue gases need to be forced out.
They need to be forced because a lot of the heat was removed from the gases. The heat these gases need to rise up a flue and be dissipated into the atmosphere. It also causes moisture in the gases to condense any moisture. Therefore, a drain is needed to drain the excess moisture from the system. A non-condensing boiler has a single heat exchanger, and the gases rise naturally because of the heat contained in them.
The heat helps the gases rise out of the flue and into the atmosphere. That is not the case with a condensing boiler because it utilizes much of the heat before it is ejected into the atmosphere.
Boiler Efficiency Options - Zoning
Zoning offers another efficiency option for a boiler installation. The hot water boiler loop piping arrangement can be designed in such a way as to allow branches of the loop to be zoned. In addition to the piping, you need zone valves and thermostats for each zone. The boiler controls are also different in a zoning arrangement. Individual rooms can be zoned to accommodate their very own thermostat.
In unoccupied rooms, you can set the temperature to a lower setting, so heating is only needed when the room is occupied. The theory is that you only need to maintain minimum temperatures in unoccupied rooms while the occupied rooms are heated to comfortable temperatures.
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