• Tag Archives Natural Convection
  • WHAT IS A GRAVITY HEATING SYSTEM? – Gravity Convection Heating Revisited

    The three (3) basic elements of hydronic heating are heat generation (boiler), distribution of energy (pumps) and conversion to area warmth (radiation). Of these hydronic distribution is typically the least understood, generally misapplied and needs revisiting.

    What is a Gravity Heating System? A century ago all water-based hydronic heating (hot water and steam) employed the natural gravity attributes of heated water and water vapor (steam) to distribute energy. NO DISTRIBUTION ENERGY WAS REQUIRED! These were effectively single-zone systems that could only be modulated by varying the energy input of the boiler and the radiation outputs using register dampers or steam radiator vents, respectively. Natural (gravity) convection of heated water underlies all hydronic distribution, yet is not considered in contemporary practice. So, check-valving is installed to negate its less desired effects.

    The introduction of electric circulation pumps in the 1920’s enabled forced hot water heating (FHW) and changed hydronics forever. Gone was the large, pitched piping and radiators, replaced with zoned heating and finned radiation. The heating market never looked back, and justifiably so. Underlying this however remained the natural gravity convection effect that had to be controlled using check-valving as noted within the system.

    Early electric circulation pumps (circulators) were large, power consumptive and constructed of discrete components, i.e. motor to coupling to pump. We “old-timers” have vivid memories of failed couplings of varied types, seized and leaking pumps and smoked motors. The advent of wet-rotor circulators was like manna from heaven, reducing circulator issues with greater longevity and reduced power consumption benefits.

    Now the evolution and introduction of particularly Delta-T (differential temperature sensing) ECM Circulators projects hydronic distribution management to an entirely new level. Integral instrumentation and operational data display of these circulators provide us with finite attribute identification and application control.

    The focus of our work has been to optimize this hidden contribution of natural gravity convection as both a distribution energy saver and a selective fail-mode feature in hydronic heating. As such the Delta-T ECM Circulator has been the crucial tool in the development of our “Delta-T ECM Hydronic Heating Appliance”. We claim optimization of natural gravity convection within our boiler, near-boiler distribution piping and distribution energy requirements using a dedicated Delta-T ECM Appliance Circulator. Citing an automotive analogy, we refer to it as “putting an Automatic Transmission on a Boiler™”. This intelligent, variable speed circulator is effectively a hydronic CVT (Continuously Variable-Speed Transmission) in practice.

    Let’s go back to that old gravity hot water heating system of a century ago. By comparison, contemporary hydronic heating systems have smaller piping with multiple zones for heating flexibility. The old “gravities” necessarily used high-mass cast-iron boilers to modulate heating supply, otherwise control was particularly difficult when using solid fuel firing as with wood or coal. With generous distribution piping sizes and radiation elements gravity convection worked fairly well, and with NO distribution power requirements!

    Properly pipe a contemporary FHW system using a dedicated “Delta-T Mode” system circulator with complimentary low-energy ball-type zone valves vs. flow-checks yields great results! Transpose this configuration onto the old gravity system layout and you functionally emulate its performance as in the following figures.

    The advantage is in using natural gravity circulation in this contemporary upgrade. Today we have somehow lost the trade skills of enhancing gravity convection. No consideration is given to pitching, compacting and minimizing distribution piping in particular. Additional gains are available in radiation layout by using properly sized and configured series and/or split radiation loops. The 45° elbow fitting as an example saves 30% of piping and reduces head pressure significantly over a 90° elbow run. All this increased pipe volume and head pressure reduces the natural gravitational convection effect, not to mention increasing materials, labor and lifetime operating costs of the system.

    Our Delta-T Mode Circulator measures this head effect well via its wattage indicator. All of our single, dedicated system circulator Beta Site installs to date exhibit an 8 to 13 watt distribution power consumption upon a 20° delta-t (adjustable) differential attainment. Compare this to 80 watts typical for each 16gpm fixed-speed circulator or 20 to 25 watts each for the equivalent delta-t or delta-p install. With delta-t you can witness the wattage steadily decay to half or less as natural convection contributes. We refer to this as “paddling your canoe with the current”.

    A secondary effect of gravity convection seems to be radiation heating profile modification, smoothing demand amplitude variation and increasing comfort. Some of the extended fuel savings we observe and the delta-t manufacturer claims seem to be due largely to this radiation profiling effect. Another contributor is the lowered system operating temperature effect of using a very high mass cast-iron boiler vs. contemporary low-mass units. Burner operation cycles are significantly less frequent and briefer than the system it replaced.

    A personal observation: This author has never replaced a “cold shot” cracked or magnetite impaired cast-iron boiler in over sixty years of hydronic and steam installations! Perhaps a discussion for another day, but have we also “thrown the baby (cast-iron boiler) out with the bath water” to cite an old adage?

    Finally, the combination of higher boiler thermal mass with enhanced gravity convection extends selective fail-mode heating continuity substantially. Recently and four years prior our Beta Site #3 experienced a fail-safe circulator interruption. The latter an over-current condition from a voltage surge “fail-safed” its operation. In both instances the condition was not discovered for an estimated 2 to 3 days, despite significant heating demand. Neither living area heating nor indirect DHW generation were affected. Second level heating reduction was eventually noted, as it was prior. The customer called and we reset the power switch over the phone to resolve. It is also noteworthy that we have had no system related service calls in over twenty aggregated operating years on our multiple Appliance Beta Sites!

    In closing, the contemporary excesses and misapplication of hydronic distribution are troubling to this author. If tradesmen are promoting their excessive system distribution piping efforts as efficiency measures they are sorely misdirected and possibly even deceitful. Witnessing customers proudly showcasing excessively installed systems or trade supplier contests for the “prettiest system” installation pics are also particularly disconcerting. Trade practices and hence consumer perceptions need challenging. Are we selling parts ….. or performance?

    Perhaps it is time for an engineered “appliance” approach (as ours) to rein in this “Plumber’s Playground”.

    Updated 08/23/2019 P.D.M., Sr.


  • DELTA-T ECM HYDRONIC DISTRIBUTION – Really “Raising The Bar”!

    Heating and moving water (hydronics) is recognized as the most efficient method of creating and distributing warming energy. From the Roman Baths to Gravity Piped Hot Water Systems of a century ago natural convection of heated water provided a simple, if seemingly temperamental solution.

    Adding pumps (circulators) to heating water distribution has forever improved comfort an flexibility. However, their application has been less than ideal, utilizing only fixed-speed/capacity circulators, typically poorly applied to residential heating in particular. Using a “one size fits all” approach and swapping sizes to effect results has been a thorn to the trade suppliers.

    Applying switchable, multi-speed circulators has provided an interim solution to poor matching options. Further, measuring actual circulator zone supply and return temperature differentials with an infrared thermometer while selecting speed(s) has provided a more efficient solution. It’s still a less-than-ideal result, with a cost premium.

    The Delta-T (Differential Temperature Sensing) Variable Speed Circulator has been around for some years now, providing the idealized solution to heating distribution flow management. It has arguably fallen far short of its potential, burdened by high initial cost, audible operational “whine” and low speed “growling”. Occasional high load torque stalls further contributed to its unknown nature.

    Enter the ECM (Electronically Commutated Motor), the latest iteration of the “intelligent” Delta-T Variable Speed Circulator. The “heir apparent” is whisper quiet yet powerful, dramatically reduces power consumption with no “torque stalls”, displays great functional data and at a palatable cost. Taco® Comfort Solutions of Cranston, RI also claims up to 15% fuel savings along with an 85% energy drop with their 00e Series VT2218 ECM Circulator, pictured.

    Author’s Note: We former High-Tech Process Engineers were applying “Stepper Motors”, the ECM predecessors to Machine & Process Control over 40 years ago. Finally, the Heating World is getting some real tools to work with!

    The Delta-T Circulator is and has always been marketed as an enhanced replacement for a fixed or multi-speed circulator. Have a zone performance issue? Substitute a Delta-T and “tweak” it in. Problem fixed, within the constraints of the zone design and a 3X cost premium of course. This latest (and supplier exclusive) Taco® VT2218 is being very well received, breaking the “Cost-Performance Stigma” of its predecessors and counterparts. We love it!

    VT2218+ZV ultra-oil-1 HTPSuperstor

    As “High-Tech” Process and Manufacturing Engineers with a Heating Discipline we (Mercier Engineering) have further projected the Taco® Delta-T ECM VT2218 as a Dedicated System Circulator, the acknowledged INDUSTRY FIRST to do so! Reviewing its Technical Specifications the VT2218 is ideally suited to residential/light-commercial heating system applications, given that operational attributes can be accommodated. These are namely:

    1. Providing uniform heating performance under normal multi-zone demands.
    2. Simultaneously servicing an Indirect Water Heater (IWH) to optimize both domestic hot water (DWH) and heating water generation.
    3. Prioritizing DHW generation within varying area heating demands.
    4. Accommodating differential temperature branching such as radiant zone(s).
    5. Satisfying both current and future (planned expansion) demands without an efficiency penalty.
    6. Providing beneficial System Service & Reliability projections.

    Over the past fifty (50) years we have installed and monitored “conventional” hydronic (FHW) heating systems, focusing on component selections, their performance and service levels. This continual qualification process has yielded a set of Premium American Components with “zero-fail” histories, at the expense of other NAFTA, Euro & Chinese products.

    Recognizing the potential of Delta-T Hydronics Distribution as previously noted, about five (5) years ago began a concerted effort to select and qualify the dedicated system circulator application. Our independent work using three (3) successive iterations of Taco® VDT, HEC and VT/00e Products has yielded not only a viable, but a superlative Packaged Delta-T ECM Hydronic Heating Appliance™. Its performance is principally based on our Proprietary Near-Boiler Piping System that constitutes the basis of our Non-Provisional Intellectual Property Protection Submission (Patents Pending – USA & Canada).

    So what began as an “evolutionary” effort to apply a newly available “tool” in the resultant has approached a “revolutionary” one. Our Packaged Delta-T ECM Hydronic Heating System™ is actually a FHW Heating Appliance, an industry first! Placing the Delta-T ECM Circulator into a full hydronic (FHW) heating system we slogan as“Putting an ‘Automatic Transmission’ on a Boiler”. Coupling “intelligent” Taco Zone Sentry®valving (pictured), a “high-mass” boiler (Weil-McLain UOpictured)and an integrated IWH (HTP SSU45– pictured)dramatically reduce complexity and idealize hydronic system performance.

    In our introduction we referenced the “natural convection” (gravity heating) used by the Romans, et al that prefaced our “modern” hydronics. Our optimized Delta-T ECM System exhibits exceptional gravity convection qualities, continuing heating upon circulator disablement or with zone valve manual operation. Short of a full electrical outage significant gravity convection heating continues, providing a useful fail-safe protection feature.

    Now let us really “Raise The Bar”. Here is performance data taken from two (2) similar “beta test sites” in our grouping.

    100,000 BTUH System, Oil-Fired, 3-Heating Zones + IWH

    Attribute “Conventional” System Delta-T Hydronic System Comments
    System Efficiency (Est.) 87% (Boiler Only) 90++% (Aggregate) Combined Hydronic Efficiencies
    Mean Operating Temperature > 145°F (Est.) 132-140°F (Observed) Normal Heating Operation
    Distribution Power 165 Watts (Est.) 11-12 Watts (Observed) Equates to Taco® Claims
    Distribution Fuel Efficiency  N/A – 15% Consumption Per Taco® Claims
    Natural Convection  Minimal to Moderate Very Significant (Observed) Very Installation Dependent
    System Footprint < 35 Sq. Ft. 12 Sq. Ft. (Actual) Very Installation Dependent
    Construction/Life Low-Mass C.I. or Stl. + Copper High-Mass C.I. & Stl. Only  10 to 20 vs. 30+ Yrs. (Est.)
    Complexity/Maintenance/Skill Higher/Annual/Specialized Low/Bi-Annual/Standard Standard Controls Only
    System Installed Cost (Est.) $10,000+ (Est.) $7,500 (Quoted) Southern NH Region

    This is the new “Bar Height”.

    We challenge ANY Tradesman or System Installer to raise it.

    To Summarize:

    1. Delta-T ECM Hydronic Distribution is singly the most significant and cost-effective contemporary heating advancement.
    2. This technology is applicable to any fueled hydronic heating system with substantial packaging and cost benefits.
    3. System configuration using a Dedicated Delta-T ECM Circulator further reduces physical and technical complexity while idealizing hydronic performance.
    4. Our Packaged Delta-T ECM Hydronic Heating System™ is the first, true Hydronic Heating Appliance, considering its intrinsic architecture, performance and as-installed economics.
    5. This is the new Standard of Measure in Hydronic Heating.

    Author’s Note: Updated 06/12/2017