This month’s editorial calendar features boilers, so I’m going to touch on some of the issues and concerns with the design, installation, and commissioning of these units with a focus on the condensing variety. You might want to stop reading this column and pick up your handy 2020 ASHRAE Handbook, HVAC Systems, and Equipment, to refresh your knowledge of boilers by reading Chapter 32, Boilers. The chapter’s table of content provides a series of important topics, but, surprisingly, the chapter doesn’t address boiler combustion air, ventilation, servicing, troubleshooting, maintenance, or commissioning of the equipment.
Here is a list of things to do when designing condensing boilers for a heating and ventilating project application:
1. Identify the optimum boiler for the job.
Boiler manufacturers offer a wide variety of units. Each type has appropriate applications dependent on its design intent as well as whether it’s a water or steam system. “Selection Parameter,” on page 32.5 of Chapter 32, gives the designer a lot of selection considerations as well as considering engineering the optimum boiler configuration, e.g., lead-lag, three boilers at 50% capacity so the third boiler is standby, etc.
2. Focusing in on the condensing boilers, the design engineer will have a lot of flexibility with this type of application because these boilers can operate at lower hot water heating temperatures and are considered highly efficient equipment.
Condensing boilers can be specified to be firetube or watertube to meet the design intent. This equipment doesn’t require the more demanding and costly boiler breeching and chimney stack that other types of boilers require for combustion air exhaust.
3. A useful design consideration when laying out a boiler room is to create an access walkway around the boiler(s) for maximum servicing. Consider it a service technician’s highway. In addition, a floor drain should be provided adjacent to each piece of equipment for draining water when servicing it.
Caution is needed when accommodating the condensate expelled from a condensing boiler because it is acidic with a pH between 3 and 4. The acidic nature of the condensate may be corrosive to cast-iron plumbing, waste pipes, and concrete floors but poses no health risk to occupants.
4. Boiler rooms should have a means for combustion air and ventilation air to ensure the space will be under an equal or positive pressure.
It is not recommended the room be under a negative pressure. Often, this equipment can be installed with directly connected outdoor air duct or PVC pipe to the boiler-burner section so that cold air is not drawn through the room before reaching the burner section, especially during the heating season.
5. For hot water systems, the engineer should decide during design to specify a chemical treatment workstation that includes an eye-washing device to protect the technician while maintaining system chemical treatment level.
All too often, the design layout of the boiler(s) and associated pump(s) are void of maintenance features and “serviceability” that makes the equipment difficult to maintenance.
6. Coordination is required with every boiler installation.
The electrical design engineer will want to know the electric data and whether emergency power will be required. The plumbing designer will want to know if a floor drain is required adjacent to the boiler(s), will there be a means to control the acidic condensate draining from the unit, what are the city water requirements, is a backflow preventer present, and is gas pressure relief piping available to the outdoors. The structural engineer will want to know if a housekeeping pad is required.
7. Consider whether redundancy will be required.
As a rule, redundancy is always a good thing, even though service companies have quick access to replacement parts.
Next month, I will follow up on this discussion by asking Alexa to please manage my boiler plant.