• Tag Archives Delta-P
  • 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 desperately 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 never 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. Lost however was “free” natural gravity convection effect that now had to be also controlled by using check-valving 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. The inherent integral instrumentation features and operational data display of delta-t circulators also provide us with finite attribute identification and application control.

    The focus of our work has been to optimize the innate, but 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 “Neo-Gravity Delta-T ECM Hydronic (FHW) Heating Appliance™” (U.S. Patent 10,690,356, Canada to follow). We claim optimization of natural gravity convection within our boiler, near-boiler distribution piping with distribution energy requirements using a single, 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 again 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” employed high-mass cast-iron boilers with larger piping to modulate heating supply, otherwise control was particularly difficult when using solid fuel firing such as with wood or coal. Generous boiler sizing, distribution piping sizes and radiation elements gravity convection worked fairly well, and again with NO distribution power requirements!

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

    The advantage is in applying natural gravity circulation to the contemporary upgrade. We have seemingly lost all trade skills in managing or enhancing gravity convection. No consideration is ever given to pitching, compacting and minimizing distribution piping in particular. Additional gains are available in radiation layout by using properly sized and configured perimeter 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 with typical 4 GPM flow upon a 20° delta-t (adjustable) differential attainment. Compare this to 80 watts typical for each 16 gpm fixed-speed circulator or even 20 to 25 watts each for the new delta-p installs. With delta-t stabilization you can then witness circulation wattage steadily decay to half or less as natural convection contributes. We refer to this effect akin to “paddling your canoe with the current”. Takes a lot less effort ….. and power!

    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 also significantly less frequent than the systems they replace, increasing component lives and lowering maintenance costs.

    A personal cast-iron boiler observation: This author has never replaced a “cold shot” cracked or magnetite impaired cast-iron boiler in over sixty-five 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 the old adage? Commentary in the recent 2019 Annual Boiler Report would seem to support our contention. Read our “reading between the lines” blog on this report.

    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 thirty 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 prolific  system distribution piping efforts as efficiency measures they are most 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 and labor ….. or performance?

    Perhaps it is time for our engineered “appliance” approach to rein in “The Plumber’s Playground©”.

    Updated 11/28/2020 P.D.M., Sr.


  • THE DELTA-T ECM CIRCULATOR POWERED HYDRONIC HEATING SYSTEM

    You have undoubtedly noted the creep of computer technology into most everyday home appliances. Everything has digital displays, clocks, menus, etc. that allow varied cycling options. These purportedly provide finite control over the appliance function (and yet another clock to blink 12:00 forever or to be reset after every power failure).

    The exception is your heating system. Home appliances are typically “closed-loop” systems, i.e. they execute a task in a contained environment.  However, if there is a digital display on a boiler, it is of temperature, operation status and failure modes as applicable. Furthermore these appear predominantly on gas-fired vs. oil-fired boilers. Why? They indicate boiler control system conditions only, not the performance of the total system, and they can’t.

    Hydronic (hot water) heating systems are comprised of three elements, a hot water generator (boiler) delivering through a distribution network to radiation (baseboards, radiators, heaters, etc.) that may exhibit infinite characteristics and combinations under varying climatic conditions and demands. Try to specify a boiler for any existing distribution network as a replacement item and you quickly realize that it is virtually impossible to “get it all right”. Reviewing our other blogs you will note the amount of effort given to remedying distribution network issues, particularly on existing installations. Headaches!

    Each zone (task) in a hydronic system must be supplied with the correct flow rate (gpm) of heated water for best performance. Currently this can only be done only with a properly selected circulator for each zone. The multi-zoned circulator distribution system is therefore the contemporary, preferred option.

    But what can be done with single-circulator, multiple zone valve systems? The short answer is that they by design can do nothing well. Their attraction has been initial cost offset by energy, performance and maintenance costs over system life. In fairness though, on smaller two (2) to three (3) zone systems they can perform respectably, if not perfectly. Hidden is the innate penalty of energy operating costs.

    Ironically, the direction to an efficient, reliable and cost-effective hydronic heating can be the single-circulator, multiple zone valve systems we just scorned — but with a very different circulator and very different zone valves!

    First and foremost a hydronic (hot water) boiler must be sized (capacity) to match and at worst case nominally exceed the heating demands of the total structure. (Refer to our blogs again.) This value must be determined through measurement and with the use of a Heat Loss Calculator. This value and this value only can determine the properly-sized hydronic boiler for your application. (Note: We specify and use Weil-McLain Ultra Series products exclusively, but we are terribly biased!)

    Link http://www.weil-mclain.com/en/assets/pdf/UltraSeriesBrochure.pdf

    It should be readily apparent that the objective is to supply the ideal amount of heated water to each zone, appliance or storage tank according to its current demand. This can now be accomplished by delivering the varying demand of heated water through an “intelligent” circulation system.

    There are two (2) variations of these, employing different principles:

    1. The Delta-P Method (Δ-P) where P = Pressure: Employs a full-demand capable conventional circulator pump configured within a by-pass loop containing a mechanically variable Pressure By-Pass Valve. Operationally the pump operates continuously and at full capacity providing a preset pressure delivery while returning the excess delivery to the boiler. We recently installed one of these systems. Works well so far, but additional pipe-fitting and valve required with continuous, fully powered circulator operation.
    2. The Delta-T Method (Δ-T) where T = Temperature: Employs an “Intelligent” Circulator on the output of the boiler that infinitely regulates delivery by maintaining a preset temperature differential between the supply and the return sides of the distribution system. Two (2) Temperature Sensors strapped to the supply and return lines near the boiler control the circulator speed (delivery rate). Taco Delta-T ECM Circulator found at this link: http://www.taco-hvac.com/uploads/FileLibrary/100-68.pdf

    Note: We strongly favor the Delta-T Method and thus the impetus for this blog.

    The other half of the Intelligent Hydronic Heating System is the Zone Valving that should be mounted beyond the System Circulator, after the air eliminator/air scoop at the end of the supply manifold. We strongly recommend and use only the new Taco Zone Sentry® Zone Valve Series found at this link: http://www.taco-hvac.com/uploads/FileLibrary/100-82.pdf. They feature:

    1. Well ported ball valving to minimize flow resistance.
    2. Quicker actuation.
    3. LED status indicator lamp.
    4. Very low energy consumption.
    5. Manual over-ride capability.
    6. High reliability.
    7. Low cost.

    Let’s define the specifics of the common system scenarios:

    1. New System Installation – Configure exactly per our prior discussion and details.
    2. Full Existing System Upgrade
      • Resize and replace boiler with a correctly sized and configured unit.
      • Replace all existing circulators with an intelligent “Delta-T” Technology Circulator.
      • Replace any zone valves with the specified “Zone Sentry” Valves.
    3. Partial Existing Zone Valve System Upgrade
      • Resize and replace boiler with a correctly sized and configured unit.
      • Replace individual zone circulators and valves as viable.

    System Design Notes:

    1. Intelligent Boiler Systems necessarily use “Cold Start” Hot Water Only Boilers. Immersion-style DHW Coils cannot be accommodated and therefore Indirect Water Heaters are typically used for domestic water generation efficiency.
    2. System Circulators employed by design in Condensing Gas and Multiple Boiler Systems must be retained! The Intelligent Circulator must be added to the distribution supply line outside of the “Boiler Loop” that maintains through-boiler circulation. READ AND FOLLOW YOUR BOILER MANUAL SPECIFICATIONS!
    3. Delta-T ECM Circulator selection is crucial not only for thermal flow capacity to match the boiler output, but for head (effective resistance) of the total system. Larger, multi-level systems need particular attention in this regard. Nominally over-sizing a Delta-T ECM Circulator will incur little penalty due to its innate efficiency and flexibility. However, under-sizing it will quickly exhibit a performance penalty.

    The Delta-T ECM System by design provides controlled, heated water within a preset, adjustable range to all distribution elements of a hydronic system. Moreover it does this irrespective of the number, size, duration and function of the distribution elements and their infinitely variable demand patterns. In so doing it becomes in effect a “self-balancing” system, eliminating hydronic noise (whistle) from over-driven zones while minimizing heating lag resulting from under-driven (lazy) zones.

    Note: The Delta-T ECM Circulator with its built-in controls is about three times that of a conventional one, but you need only one.

    The value of a Delta-T ECM System as a diagnostic tool, particularly as a replacement system upgrade should not be under-emphasized. If it doesn’t fix or improve existing distribution issues, it surely will point out any other deficiencies and isolate them for correction. As a radiation assessment tool in particular you can now properly balance rooms using the radiation dampers, and if not identify and supplement radiation as necessary.

    To summarize, it’s a terrible system:

    1. Terribly simple
    2. Terribly efficient
    3. Terribly inexpensive

    We encourage you to view our Packaged Delta-T ECM Hydronic (FHW) Heating System (Patent Pending) on this site for additional detail.

    Ed. Note: Updated 03/27/2017