A Systematic Approach to Hydronic Design: the 4 Essentials

Modern boilers are effective primary heat sources by themselves, but can also be used as backups to higher-efficiency systems such as geothermal or solar-based heating. When installing or adding a boiler system, designers, engineers and building owners should adhere to hydronic design essentials that favor a total system approach to design and implementation. By applying the following four hydronic design essentials, a boiler system can be built that will provide years of reliable and efficient indoor heating.

The Four Hydronic Design Essentials

1. First Cost

First cost or initial investment is the amount of money that must be spent on hydronic equipment that forms the basis of your heating system. This usually refers to spending on whole systems, but can also include components or features that boost efficiency or performance. Granted, the first cost of a hydronic heating system can be high, but modern technology has produced a range of options that can be combined to lower overall costs while boosting efficiency. For example, rather than buying a large-capacity modulating condensing boiler, a smaller unit can be combined with a non-condensing unit to achieve good results at a lower cost. The modulating condensing unit can handle low-temperature water during start-up and circulation, while the non-condensing unit can provide standard heating once water is heated to operating temperatures.

2. Life-Cycle Cost

Life-cycle cost refers to how much it will cost to operate the hydronic system over its expected lifespan. For most boilers and related components, this lifespan can be several decades. Life-cycle cost usually includes consideration of the first cost as well as fuel expenses, maintenance, repair and electricity. When calculating life-cycle cost, adjustments must be made to future costs to ensure the total is realistically converted to allow comparisons in current dollars. Life-cycle cost provides one of the most important pieces of information derived from hydronic design essentials: the payback period. This lets buyers know when savings from efficiency improvements or other benefits of the new equipment will equal the initial amount spent on the equipment. When this point is reached, the equipment will have paid for itself. All performance thereafter can be assessed as part of the benefit of using high-efficiency systems.

3. Annual Efficiency

Efficiency remains a primary consideration when installing hydronic equipment or any sort of HVAC system. Boiler efficiency is indicated by the unit’s Annual Fuel Utilization Efficiency, or AFUE, a number assigned by government-standard testing. AFUE indicates how much of the energy in the fuel used by the boiler is converted to usable heat. An AFUE 90 percent boiler, for example, will turn 90 percent of the fuel used by the boiler into heat, while the remaining 10 percent is lost. Currently, gas-fired boilers must carry an AFUE of 82 percent for hot water and 80 for steam. Oil-fired boilers require an AFUE of 84 percent for hot water and 82 for steam. Boiler efficiency can be improved even further by adding features or components such as modulation or staged firing. Multiple boilers of a lower capacity can be more efficient in total than one large boiler.

4. Value Engineering

Value engineering refers to assembling a boiler system according to hydronic design essentials that, in total, provide the greatest level of efficiency and value. Under this concept, boilers are properly sized to provide exactly the amount of heating capacity needed to meet the temperature demands of the building’s occupants. This is known as “heating load,” and affects the type and capacity of hydronic equipment that can be used. Boilers installed to take best advantage of value engineering concepts usually include proportional-integral-derivative (PID) controls that can respond effectively to changes in conditions such as outdoor temperatures, overall heating load, and operating stage of the boiler.

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