HVAC DESIGNERS' CONUNDRUM
HVAC Engineers today are confronted with the daunting task of designing systems to perform at maximum capacity that can also excel at part-loads. But, under existing design practices and the current state of technology for system piping networks [hydronics]; favoring system Water-Mixing conditions, that is not possible. Water-Mixing in system hydronics arises from the encountering of boiler(s) hot-water supply with system colder-water returns. Increasing Temperature in resulting mixed-tempered-water is the major threat to boiler performance operation, while poor system Thermal-Mass, Mixed-Water temperature signaling and their effect on boiler soft/short-cycling are the real culprit of overall system efficiency [AFUE]. Boiler cycling is not a simple phenomenon and it arises from the interactions that take place between two or more of the processes described above. There are system conditions that arise from optimal performance of the heating system’s terminal units and/or Domestic Hot Water [DHW], and there are system conditions that are optimal for efficient boiler(s) performance. Under the current state of technology, these two set of conditions are rarely, and perhaps only accidentally, the same. What is optimal for the former is usually not optimal for the latter, and vice versa. Attempts by designers to accommodate the needs for the boiler when designing system hydronics can; and often do, compromise the performance of their systems. Ignoring the needs of the boiler creates short-cycling, and the energy lost from it often serves to undo the gains made by state-of-the-art system designs. A designer must acknowledge that in reality there are two systems being designed – the building heating system and the boiler plant – and that their requirements are always different, usually different enough to make that difference almost irreconcilable.
The Split Buffer Tank [SBT]; and the Zero Mixing concept it encompasses, articulates the mismatch on water-supply and water-return temperatures in interconnecting system loops. SBT acts as the perfect decoupling/coupling loops point where both flows boiler(s)-supply high-temperature-water and building-return low-temperature-water can confluent and be diverted into the right path. In system hydronics; this change alone, allows boiler(s) to consistently run at Steady States Efficient operation while providing building terminal units and the DHW with the optimum heat input for occupant comfort and units performance.
On industrial sites; dependable on batch process heating, water mixing elimination removes heat capacity bottle-necking, boost heat-plant-output and improve production quality, greatly impacting the business bottom line.
Same Zero-Mixing concept and SBT-tank integration can be introduced to chiller-plants with the same energy saving advantages.
DBBS new technology moves away from the LOW - TEMPERATURE - DIFFERENTIAL concept very common on existing condensing boiler plants/chilled water systems and apply a more efficient model based on “ZERO MIXING and HIGH - TEMPERATURE - DIFFERENTIAL” concept.