|Economical and easy to upgrade||Using multiple condensing boilers for large input systems is an economical and easy way to upgrade older, inefficient boiler plants to attain outstanding energy savings. Also, in new construction, these boilers provide buildings with the highest heating system efficiencies possible. The smaller size of the IBC wall mounted condensing boilers means that in most cases the boiler room equipment can be moved into place and installed without special equipment, using the mechanical contractor’s in-house staff.|
|Incredible "turn down" capability||
Multiple IBC modulating condensing boilers give the boiler plant an incredible “turn down” capability that can respond to any building load condition imaginable.
Example: Four IBC 80-399 boilers allow load matching from an input of 80,000 BTU/h all the way up to 1.6 million BTU/h. This “right sizing” to building load increases energy savings dramatically. It is common to see fuel savings of over 30% in retrofit situations.
|Redundancy||Individual boilers can be taken off-line for service without impairing the operation of the rest of the boiler plant.|
|No extra controls are required||IBC’s SL and VFC modulating models are set up for staging without any extra controls – all that is needed is a 2-wire twisted pair connection between controllers, and simple control settings using the touchscreen. One “master” unit acts as the server, with the other subordinate units switched via the network connection.|
The roof is recommended for vent termination, doubly so with multiple units where steam plumes can be that much larger than from single units.
For sidewall applications, ensure a “sterile” wall is readily available (no windows, close neighbors), and ensure that, should condensate drip from vent terminations, it will not have adverse effects (including freeze-up) on objects or structures below.
For roof top penetration of multiple boiler sets, options are to group all intake terminals together for a common penetration through a custom cap, or to place them in close proximity, using commonly available pipe flashing. Alternatively, these boilers are certified to be installed using indoor combustion air (adequate combustion air to the boiler room must be provided by other approved means).
Ensure the following:
- Group the exhaust pipes and place the 2 separate groups (intake and exhaust) at least 3' apart. Make the closest intake and exhaust pipes 36" or more apart.
- The outdoor combustion air intakes are down-turned using 1 or 2 x 90° elbows.
- Exhaust termination pipes are 24" minimum above the intake elevation, whether roof or wall mounted.
Flue gas condensate is mildly acidic; therefore, use condensate neutralization when disposing condensate into drainage systems containing cast iron or copper pipe and fittings. Also use neutralization in locations where condensate is drained directly into a septic system.
Use a Primary/ Secondary piping configuration; a typical configuration is illustrated below.
Primary / Secondary piping is also strongly recommended for all SL series boilers. Note that a parallel multi-boiler piping arrangement, where system water runs through all boilers regardless of whether they are firing or not, may invite damage to components by overheating.
Parallel piping temperatures in the sealed boiler cabinets of dormant boilers rise to the system water temperature, whereas with primary / secondary piping, flow is always accompanied by fan operation that maintains cabinet temperature within the proper limits. In parallel piping, damage to the boiler or site is not covered by warranty.
For optimum efficiency, and smooth operation in staging, we require multiple IBC boilers be placed in a manifold piping arrangement so that all units receive the same (cool) return water temperature. Use check valves to prevent induced circulation through “off” units.
There are three basic methods for controlling a multi-boiler set:
- Fully Autonomous: involves designation of a Master boiler which will receive all sensor and dry contact call-for-heat signals, manage the secondary pump(s) and, via BoilerNet connection, coordinate firing of all subordinate boilers. This fully autonomous approach utilizes IBC’s internal heat regulation and boiler management software.
- Semi-autonomous involves a remote analogue signal to the Master boiler’s External Control terminals. This signal corresponds to a target set-point temperature, with the range scaled according to the programmed min-max temperatures. IBC’s multi-boiler heat regulation algorithm still determines which boiler fires, throttle levels etc., but to an externally determined operating temperature. Call-for-heat to the Master can be conveyed via a 2.1+ VDC signal on the External Control terminal, or a dry contact boiler enable with the 0-10VDC input for target temperature.
- Classic-DDC control, involving separate dry-contact calls and throttle control signals to each boiler from external DDC. (Not generally recommended.)
The majority of IBC multi-boiler applications use the full autonomous method above, and the remainder of this topic focuses on this method.
IBC boiler networks are designed for single load applications and certain two-load systems. Three- or four-load sequential management strategy, popular on single boiler residential systems, do not typically scale up to larger multi-boiler applications. Large systems imply significant thermal masses which generally cannot change temperature quickly.
The IBC controller can control up to four load pumps that are zoned for the same temperature. However, for multiple-temperature applications, use external mixing valves or injection control for cooler demands, or IBC’s “Opt-out” strategy. See the Benefits of the domestic "opt-out" option.
Inter-boiler / network connection:
- Use polarity-sensitive twisted 2-wire leads (CAN bus standard) to join one boiler to the next (to a maximum of 24 boilers). Connection is made between the “Boiler Net” terminals near the base of the TB2 terminal strip. Wiring between boilers needs to be a sequential “daisy chain” approach. See the wiring diagram below.
- Controllers must be powered off during boiler net wiring. Network wiring should not run in parallel to any nearby line voltage wiring.
When three or more boilers are networked, removal of a circuit board jumper (as illustrated below) is necessary.
To remove jumpers:
- Turn off power to the boilers.
- Remove the control board covers from each intermediate (non-terminating) boiler in the array.
- Locate the jumper clips at the bottom right of the circuit board. There are two of them. The jumper for configuring multi boiler operation is the JA02 shown in the drawing below.
- Pull this jumper clip straight away from the two pins on the circuit board, and store it somewhere safe in case it might be needed in the future. Common practice is to place it so that it hangs onto the bottom pin only.
- Replace the control board covers, and restore power to the boilers.
Wire each boiler’s primary pump to that boiler’s primary pump harness lead. The image below shows the primary pump leads (yellow and white wires) located in the wiring box behind the control.
Bring all thermostat, sensor and secondary pump leads to one unit – to be declared as Boiler 1 (Master) in the software settings stage (below). See Benefits of the domestic "opt-out" option for exceptions.
- Outdoor Sensor -- For Reset Heating functions, connect one of the supplied outdoor sensors to the Master boiler only at the “Outdoor Sensor” terminals. There is no need to link up the other boilers with the outdoor sensors supplied with those boilers (unless configuring an Opt-Out load for Reset Heating).
- Secondary loop sensor – connect to the master boiler. Place an immersion or strap-on sensor on the building loop, downstream of the injection point from the boiler plant into the system piping loop. Use either IBC part P-216 Secondary Loop Sensor with Well Kit, IBC part 240-033 Secondary Loop Sensor, or use a Type II 10KΩ sensor such as the tekmar 071. A secondary loop sensor is a primary control requirement for coherent management of a multiple boiler set.
- DHW sensor – connect to the master boiler only if the boiler plant will be dedicated entirely to DHW. Connect to the opt out boiler if the opt-out option is to be used (see Benefits of the domestic "opt-out" option).
These outputs for a 4-20mA variable speed signal are typically not used: see Boiler Status memo for more details.
To establish a network using the master (lead) boiler's touchscreen controller:
- Tap the Standby screen.
- On the Main Menu, tap the Installer Settings tab, and tap the Multi-Boiler tab.
- Tap the entry box next to Boiler ID, and from the keypad select 1 to set the default value from 0 to 1.
- Tap the entry box next to Master Boiler, and tap Yes and then OK (for Master boiler only – leave all other boilers set to No).
- Tap the entry box next to Staging Delay, and from the number keypad, set the minimum delay time before the next boiler comes on line (must be at minimum equal to time for closed-loop water to complete one full circuit of system. For large mass systems, allow for two or more loop times).
- Tap the entry box next to Rotation, and tap On and then tap OK. This balances the run time on each of the boilers. There is a 48 hour maximum allowable runtime difference between boilers.
If you are prompted to Restart, tap Cancel, and go back to the Multi Boiler Settings screen.
- Tap the entry box next to Fixed Lead, and tap On, and then tap OK. When set to On, the Master boiler is always the first to answer a call for heat. In the “Off” state, the boiler with the least runtime is the first to answer a new call for heat. Note: This feature is over-ridden when Rotation is On (treated as Off).
- Tap the entry box next to Firing Order, and tap First On / Last Off and then tap OK. "FirstOn / FirstOff" promotes more balance run times while First On / Last Off allows for wider turndown ratios when a smaller model boiler is chosen as a master of larger model boilers.
Tip: To speed up confirmation of system operation, move the Staging Delay to 1 minute to witness proper operation of the call up of other units.
- Tap the Save button to save the changes.
- Go to each boiler:
- Follow steps 1-2.
- Tap the entry box next to Boiler ID, and assign a unique ID address. For example, 2, 3, 4 etc. (up to 24 units allowed).
- Tap OK.
- Tap the Save button.
The controller prompts you to approve a restart. After restarting you can confirm network programming was successful by returning the Master’s Installer Settings / Multiboiler menu and scrolling to the bottom. The Boilers Online number should show the number of boilers networked.
- Leave loads in subordinate boilers set to Off (see Opt-out section for exceptions).
- Setup & configure heat loads on master boiler only. Use the Installer Settings menu to specify:
- A set temperature (Setpoint) or
- A Reset Heating curve.
Boiler will supply the Design Supply Temperature on the coldest days of the year (as defined by the Design Outdoor Temperature appropriate to your locality; see your heating wholesaler or contact IBC if unsure of this value). Target temperature will be continuously modified according to the outdoor sensor inputs.
- An External Control signal (default 0-10 VDC) is being sent to the External Control terminals.
In all cases be sure to reassign the Water Temp From (Water° From) parameter to Secondary Loop.
For more information on load settings, see the V10 touchscreen controller manual.
The domestic opt-out function allows individual indirect storage water heaters to call up a single boiler to turn on a DHW boiler pump, divert its fluid flow and heat production directly to the tank, while turning off the boiler pump that injects heat into the heating mains, therefore bypassing the system piping.
This operation all but eliminates piping losses. As a further benefit, when the boiler plant is operating in heating mode, the DHW boiler(s) can “opt-out” of the heating load, allowing the rest of the boiler plant to continue the heating task uninterrupted. If optout boilers are in the process of making DHW when a setpoint or heating demand is received by the master boiler, the remaining boilers will switch over to that load leaving the opt-out boilers to make DHW. If a DDC system or other external control is used to operate individual boilers the DHW opt out feature is unavailable.
DHW opt out is still available when external (remote) setpoint control is used.
Good design practice for an opt-out system dictates that the heat exchanger for the indirect tank be capable of transferring the full output of the boiler at high fire. This will result in fast recovery of the tank so that the boiler can return to the heating load quickly, and will allow the boiler to heat up the tank at lower delivery temperatures, enhancing condensation of flue products for maximum efficiency.
DHW “opt-out” boilers cannot be configured as the Master boiler without DHW operation disrupting the boiler
Opt-out loads are programmed on the opt-out boilers only. As long as the opt-out load is active that boiler will not be available to the network. The boiler will switch on the opt-out pump directly. Any pump being directly switched by an IBC control board must draw less than 4A. On set-up of opt-out load, for Boiler Pump select Off.
The screen will prompt for confirmation that a pump will provide flow through the heat exchanger.
Either a DHW sensor or aquastat can be used to generate call for DHW for an opt-out boiler. The call for DHW goes to each opt-out boiler separately as shown in Figure 7.