NABCEP SHSI key terms

A device that absorbs incoming solar radiation and transfers the captured heat to a fluid, usually water, glycol mixture, or air, for later use in space heating, water heating, or pool heating.

A solar collector with a flat absorber plate under a transparent cover and behind insulation, suited to moderate temperature rise; common in domestic hot water and space heating systems.

A collector in which absorber tubes sit inside vacuum-sealed glass tubes, reducing heat loss so the collector performs well in cold or windy conditions and at higher temperature differences.

A surface treatment on the absorber that absorbs a high fraction of solar radiation while emitting little infrared radiation, raising efficiency by reducing radiative heat loss from the collector.

The fraction of incident solar radiation that a surface absorbs rather than reflects or transmits; a high value on the absorber improves heat capture in a solar collector.

The ratio of infrared radiation emitted by a surface to that emitted by a perfect blackbody at the same temperature; low values on absorbers reduce heat loss from collectors.

The projected area through which solar radiation enters a collector, excluding frame and mounting; used with irradiance data to estimate the solar energy input to the system.

A factor that adjusts collector efficiency for the angle at which sunlight strikes the glazing, since performance drops at steep incidence angles compared with perpendicular irradiance.

The maximum temperature a collector reaches when fluid is not moving and useful heat is not being removed; a design limit that drives component selection and overheat protection.

A no-flow condition in which the collector loop stops circulating, often because the storage is fully heated or power is lost, causing high temperatures and possible fluid degradation.

The liquid that carries heat through a solar thermal loop, commonly a water and propylene glycol mixture chosen for freeze protection and high-temperature stability.

The percentage of propylene glycol in the heat transfer fluid, which sets freeze protection and boiling point; it must be checked and maintained against the manufacturer's specification.

A design and operating strategy that prevents water in a solar loop from freezing, using glycol, drainback, or recirculation so pipes and collectors are not damaged in cold weather.

A solar thermal design in which the collector loop drains by gravity into a reservoir when the pump stops, leaving collectors and exposed piping empty to avoid freezing and overheating.

A vessel in a closed solar loop that absorbs the volume change of the heat transfer fluid as it heats and cools, limiting pressure rise and protecting components from overpressure.

The portion of a building's total heating or hot water load supplied by the solar system, expressed as a fraction or percentage and used to size collectors and storage.

The calculated heating or hot water demand a system must meet under specified design conditions, forming the basis for sizing collectors, storage, and heat exchangers.

An insulated vessel that holds heated water or fluid for later use, buffering the mismatch between when solar energy is collected and when the building needs heat.

The layering of water by temperature in a storage tank, with hotter water at the top and cooler water at the bottom, which improves usable capacity and collector efficiency.

A device that transfers heat between two fluids without mixing them, such as from a glycol collector loop to potable water in a storage tank or load-side circuit.

A solar thermal circuit in which the heat transfer fluid circulates repeatedly without contact with the atmosphere or the potable water supply, typically using glycol for freeze protection.

The circulator that moves heat transfer fluid between the collectors and storage, sized to provide adequate flow while overcoming pipe, fitting, and heat exchanger pressure losses.

A control that turns the solar loop pump on when the collector sensor is sufficiently hotter than the storage sensor and off when the temperature difference falls below a set threshold.

A probe, often a resistance temperature detector, mounted at the collector outlet and in storage to report temperatures to the controller for pump switching, protection, and monitoring.

A target value programmed into a controller, such as the storage temperature at which the solar loop stops or the temperature difference that starts and stops the pump.

A safety device that opens automatically to release fluid or vapor when loop pressure exceeds its setting, protecting tanks, piping, and collectors from overpressure damage.

The angle at which a collector is raised from horizontal, chosen by latitude and season to maximize useful solar gain for the intended heating application.

The compass direction of the sun's position, measured in degrees from north, used to orient collectors and to assess shading from buildings, trees, and other obstructions.

The moment when the sun crosses the local meridian and reaches its highest point for the day, producing peak irradiance and the shortest shadows for collector placement checks.

An evaluation of obstructions that block sunlight from collectors during critical hours, using solar path data or site measurements to confirm acceptable solar access.

A deliberate load or radiator that sheds excess solar heat when storage is hot, reducing stagnation temperatures and protecting the heat transfer fluid from degradation.

A dry pocket installed in a pipe or tank that holds a temperature probe so it reads fluid temperature without direct contact or leakage risk, and allows probe replacement.

The process of pushing clean fluid through the solar loop before charging it, removing debris, solder residue, and old fluid that could clog components or degrade performance.

Removal of trapped air from the solar loop during filling and commissioning, since air pockets stop circulation, cause noise, and can damage pumps through cavitation.

A commissioning step in which the loop is filled to the specified pressure and observed for a period to confirm no leaks before the system is put into service.

The documented process of verifying that an installed solar heating system operates as designed, covering filling, purging, controls setup, performance checks, and handover to the owner.

The volume of heat transfer fluid moved per unit time through the solar loop, which must match collector and heat exchanger requirements for efficient heat transfer.

The loss of fluid pressure as it moves through pipes, fittings, valves, and heat exchangers; pump selection must overcome the total drop at the design flow rate.

A handheld optical instrument used to measure glycol concentration in a fluid sample, confirming that freeze protection meets the design specification during service visits.

Scheduled inspection and service of collectors, pumps, controls, fluid, and safety devices to keep a solar heating system efficient and to catch faults before they cause failures.

A safety procedure that isolates energy sources and applies locks and tags so equipment cannot be energized or started while workers service or repair it.

Clothing and gear worn to reduce injury risk, including gloves, eye protection, and fall protection, selected for tasks such as handling hot fluid and working at height.

The risk of scalding or contact burns from hot collectors, piping, and stored water, managed by isolation, warning labels, temperature limits, and appropriate protective equipment.

Practices for working on roofs, including fall protection, ladder placement, load limits, and weather checks, to prevent falls and injuries during installation and maintenance.

A passive solar water heating design in which heated fluid rises naturally from a collector to a storage tank mounted above it, eliminating the need for a circulation pump.

A pipe inside a storage tank that delivers cold incoming water near the bottom, preserving thermal stratification and preventing mixing with hot water at the top.