• Tag Archives 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 our 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 lessening 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 continues. 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 this adage?

    Finally, the combination of high thermal system 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 field 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.

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


  • DELTA-T ECM HYDRONICS – Redefining “The Plumber’s Playground”

    Hydronic heating comprises warming water as a medium, moving and expending its energy to warm an environment. Thus we have boilers as heat generators and radiation to convert heated water into warmth. Between these we must distribute our medium via pipes, pumps, valves and controls to meet heating demands.

    Basic hydronic system design rules of course must apply, but by and large the final product interpretation has been left to the tradesman/installer. This individualization provides a very attractive latitude of self-expression. Like an artist painting on a new canvas individual skills, styling and practice all comprise the final “picture”, with the author’s “signature” applied. Based upon our field observations we have come to refer to hydronic distribution in particular as “The Plumber’s Playground”, and with no apologies offered.

    Unfortunately the Laws of Physics apply equally to hydronic system installations as to any other enterprise. Therefore that maze of pipes, valves, circulators, controls and wiring evidenced in a “plumbers playground”, no matter how pretty, daunting or impressive is unnecessarily complex, costly and under-performs. In fact any system installed within the past three years or more not employing Delta-T ECM Hydronic Distribution Technology specifically is woefully under-performing!

    The Heating Game has changed, led by the Taco® Delta-T ECM VT2218 Hydronic Circulator and its supporting Taco® Zone Sentry Valves. We refer to it as “The Hydronic Revolution”, as it truly is! These two (2) devices, properly applied, can and do dramatically simplify the complexity and content of a conventional hydronic heating system. Again, properly applied and supported by contemporary control systems provided by an “Intelligent” System Aquastat with idealized piping (plumbing) can further enhance performance, as our work has evidenced. Our development efforts and observations are reflected within the remainder of this presentation.

    The Delta-T ECM Variable Speed, Intelligent, Multi-Temperature-Sensing Circulator is a marvel of applied technology. Its ability to sense, measure and maintain a preset temperature differential in a hydronic circuit virtually optimizes heat transfer efficiency in a single, automatic step. Further being able to accommodate varying demands from multiple zones (circuits) virtually seamlessly as we have evidenced places it as the heart of any hydronic system. Using an automotive analogy we slogan that we are putting an ‘Automatic Transmission’ on a Boiler, but doing it hydronically.

    Now pair this Taco® Delta-T ECM Circulator with a compliment of their Zone Sentry® Zone Valves and you dramatically reduce energy consumption while gaining some further fuel efficiency. As Taco® promotes we are seeing distribution power consumption drops to 11-13 watts and in another instance to 8 watts during normal operation! Compare these with 80 watts for a single Taco® 007 and 21 watts each  for a Heat Motor Zone Valve. (The Zone Sentry® uses 11 watts, and then only in a brief actuator “charging cycle”.) Hydronic heating system power consumption is virtually never considered in design, but it should and furthermore must be!

    Piping is the pride of any plumber (ourselves included) yet in so being can become a detriment to system performance. To this point we offer that hydronic convection (the natural attribute of heated water to rise, and cooler fall) is not considered as a positive contribution to system performance, but an attribute to be controlled. As we have witnessed in our design effort however, natural convection is a measurable asset, particularly when configuring piping and placement to maximize its effect. Near-boiler piping, to employ the trade term, is crucial to maximizing hydronic performance. Compacted packaging of correct pipe sizing and layout close to the boiler displays great natural (non-powered) circulation that may not only supplement but also heat at reduced levels. We had an early Delta-T Circulator failure on one of our “beta” installations that was not discovered for an estimated 2-3 days! How’s that for convection — like “paddling your canoe with the current”.

    When you fully integrate the “intelligent” Delta-T ECM Circulator, Zone Valves and Aquastat with idealized convection you come to the conclusion that hydronic system installation is no longer a process, but functionally becomes an Appliance. Our resultant “package” is contained within its boiler footprint plus minimal rear piping space. A designer need only define system capacity, number of zones, fuel type and exhausting to define the “appliance”. Further, the application lends itself to modularization, and thus to versatility by default. Not only do we significantly reduce the material content of a system, but its labor content and installation time as well.

    Now there is both a trade and consumer option, a virtual Hydronic Heating Appliance with a fixed cost and defined, superlative performance. Our work to date has been developing a “Package Delta-T ECM Hydronic (Oil) Heating System” that achieves its higher performance by incorporating Delta-T ECM Hydronic Distribution Technology with a high-mass, lower operating temperature boiler for optimized performance. But also recognize that Delta-T ECM Circulation will work on any fueled hydronic application, putting an “automatic transmission” on ANY boiler. This obviously reduces the size, content and complexity of the “Plumber’s Playground”, but to a net performance advantage in doing so.

    To summarize, a “Hydronic Heating Appliance” is in our near future, defined by technology and necessitated by the market, like it or not. Its Performance Specification will virtually determine system performance, unlike the potpourri of present practice. Our publicized contributions are documented on our website www.BoilersOnDemand.com.  Please note that our current and following product offerings are under Intelligent Property Protection (Patent Pending). We look forward to “Boilers On Demand” in the new “Plumber’s Playground”.


  • THE “DELTA-T” FHW HEATING ADVANTAGE

    Whether you’re replacing an existing boiler or installing a new Forced Hot Water (FHW) Heating System, the procedure is the same. A plumbing/heating guy moves in with a service truck full of parts and tools, a supply house truck arrives and drops the boiler and sundry parts. Then the game begins …..

    The old boiler (where applicable) is removed by whatever means required, the ensuing mess is cleaned up, and the new boiler is moved into the area. Locating and positioning the boiler is the first task and directly determines the effectiveness of the entire installation. The preferences, methods, materials and the heuristic judgement of the installer prevails. Thenceforth the building of the “Erector Set” continues, pipe by pipe, wire by wire, device by device until the task is finally completed. It’s a slow, costly and inefficient process …..

    All tradesmen develop their own methodologies, reflecting their pride and workmanship in the resultant. Unfortunately the customer pays a premium for this both initially and throughout the lifetime of his system ….. knowingly or not! We cynically refer to boiler installations as “The Plumber’s Playground”, that last vestige of “free expression” removing us from the daily tedium of “fixing leaks and squeaks”.

    Installing or replacing a boiler should be no different than a dishwasher or a water softener, with a few more pipes and wires attached ….. and it can be! Problem is we plumbing/heating guys (ourselves included) continually lag technology. We “Old Dogs have to learn New Tricks”, and brother we have!

    Recent technology now allows us to configure a FHW (Hydronic) Heating System as a true appliance! All heating system functions excepting radiation can now be integrated into a “packaged unit”, engineering it for peak performance and value in the process. “Delta-T” (Differential Temperature) Circulation Technology is truly an evolutionary and revolutionary improvement. Developed in the “high-tech” process world, it has now become both practical and economical as applied to Residential Hydronics (FHW Heating).

    Mercier Engineering via its website www.BoilersOnDemand.com is the introductory leader of Residential Delta-T Hydronic Heating. The question is not if Delta-T Circulation will out-distance conventional Fixed-Speed Circulation, but when. Evidence the following Pictorials and Details for comparison.

    Identically Configured Oil-Fired FHW Installations          

    Conventional Oil-Fired FHW System   “Delta-T” Oil-Fired FHW System
    Typical Plumber Boiler Install - 18 hrs DTO-100T2(Exp)H4-4X6

    Features Comparison Table

    Attribute"Conventional" System"Delta-T" SystemComments
    Boiler TypeWelded Steel Plate (Example Unit)Cast Iron "Triple-Pass"15 years +/- vs. 30 Years +
    Boiler Weight270 Lbs.625 Lbs.Very High Mass - Durability
    Oil Burner TypeVarious OfferedBeckett NX (Pressure-Fired)Flexible, stable operation
    Gas Burner TypeFixed, Appliance-SpecificCarlin EZ-PRO (NG/LP) (Pressure-Fired)Appliance-Specific Interchange
    CirculationMultiple Fixed Speed Circulators onlyA Delta-T Variable Circulator w/ Intelligent Zone Valves>/ 15% Fuel Savings
    >/ 85% Electrical Savings
    Piping/FittingsCopper (Typically)All Iron & Cast ConstructionSuperior Strength/Durability
    Indirect Water HeaterVarious Mfrs. & TypesAll Stainless Steel OnlyA Lifetime of Service
    Floor Space UtilizationInstaller-dependentOptimized Package DesignMinimum Space Requirement
    Energy PerformanceInstaller-dependentOptimized Energy DesignPeaked Hydronic Efficiency
    Component SourcesU.S./Foreign Mix (Typical)"All-American" (US/Canada)Quality and Serviceability
    Installed Cost (Oil example shown)"Over $10,000" (Oil, as shown)$7,000 (Oil, as shown)Price, Performance, Value

    Notes:

    1. Estimated service lives are from our and our collaborating serviceman’s actual field experience.
    2. Fuel & Electrical Energy Performance per Taco, Inc. published testing data.

    Reviewing our Comparative System Photos will will confirm many of the suppositions in our “Features Comparison Table” above. The immediate impression is one of excessive plumbing and space consumption of the Conventional System. In fact the “Delta-T” System occupies 1/3 of the space, uses 1/2 of the near-boiler piping (with no copper), with only one (1) Circulator, fewer valves and fittings ….. and with optimized hydronic flow and distribution performance! Flow is so idealized in fact that under certain component fail modes “gravity induced circulation” will continue to provide heating at a reduced level! (Patent Pending)

    Arguably a high-mass (heavy) “Delta-T” System will outlast two (2) Conventional FHW Systems with a higher Hydronic Total System Efficiency at 1/3 the “life-cycle” cost.

    So when your potential FHW Heating System Installer comes calling, ask him first about “Delta-T” Circulation. If it draws a blank stare, send him home to call Taco, Inc. — and that another “Old Dog” told you to do so. After all, you the customers are deserving of all the “New Tricks”!


  • OUR UNPOWERED FORCED HOT WATER (FHW) GRAVITY HEATING SYSTEM

    Yes, we have an oil-wood (or coal) central heating system in our home that can fully function without ANY electrical power through outages and uses less power in normal operation as well. How? Gravity induced convection heating. It was initially installed in 1975 and been incrementally improved to date.

    We are unabashedly Weil-McLain Heating System Designers and Installers. This does not mean however that we kowtow to the heating fuel suppliers and pay-as-we-go! Living in rural, frosty New Hampshire our economic fuel options are limited to oil and wood only. (Propane is a substantial premium and Natural Gas is not available.) So it is not surprising that many of us use wood or a mix of fuels to survive economically. Therefore, wood, wood pellet, coal stoves and wood boilers.

    Particular evidence of this heating trend is the recent popularity of external wood boilers (Metal Storage Sheds with a smokestack sticking up out of them) that occupy many rural yards, next to a large woodpile. (Not to mention the well worn path from the house to the wood boiler!) As a facet of our enterprise we mention interfacing our Weil-McLain FHW Boilers and converting our Steam Boilers to accommodate them. Not surprisingly we get inquiries by sometimes frustrated users to assist in making the wood boiler work well with their central heating boiler. The stories can be a bit humorous, in fact.

    Let us first describe our subject system with the intent to provide you with the principles and applications we employed and from which you may benefit in your application(s).
    We have two (2) single-fuel boilers, centrally located in the basement level of a large split entry home that we built in 1970:

    1. A Weil-McLain Model 568 Oil-Fired Boiler, installed in 1995 and subsequently “tweaked” for performance.
    2. A 1935 Vintage National Heating Co. Economy No. 64 Wood Burner. Found, reconditioned and installed in 1975. A museum-piece that still runs very well.
    3. A 40 gallon “Hot Roc” Stone-lined Storage Tank coupled to the Old National that prevents a boil-off if it is overcharged with wood or used (carefully) for extra hot water (heating) storage.

    These boilers are commonly coupled to an overhead supply manifold and on-the-floor piping between return manifolds, physically separated by ten (10) feet. This layout provides for a simple, pure convection loop between them. NO CIRCULATOR IS REQUIRED!

    There are three (3) circulator driven heating zones off the Weil-McLain manifolds. These are FloChek Valved off the upper supply manifold with circulators on the return manifold.
    The two (2) upper (main) level Living and Bedroom Area Zones are of Split Loop Configuration (reference our recent subject blog for detail) and the lower level Office and Garage Loops are a Split Perimeter and Unit Heater configuration, respectively.

    Gravity Hot Water Central Heating has been around for over 150 years but was never too popular due to its restrictive design attributes. It is functionally a single zone, single level system where building characteristics allow. There is significant lag in response to a temperature change demand and if boiler control is not absolute, temperature control suffers as well. Nonetheless, where and when you can employ convective heating it can be beneficial from a distribution energy perspective (or a lack of it available).

    Our Split Loops are fed by 1” center tapped supplies and returns that feed conventional series 3/4” radiation loops on each halves. The loops are configured with conventional 1” FloChek, manually controllable seat, opening valves on the supply manifold taps. These FloChek Valves are always included in a hydronic (hot water) system to prevent natural continuous convective heating. If one fails you have continual heating in degree regardless of thermostat setting. Note: FloChek valves may also be incorporated within a supply side circulator.

    So we can use natural convective heating to our advantage. By employing a modest upward pitch to our Split Loop supply and return lines we augment gravity convection (hotter water rises, cooler water sinks) and opening the FloChek valves we have a “controllable” energy-free heating zone. The adjective “controllable” has to be qualified by trial and error settings over varying indoor and outdoor temperature demands.

    Let’s go through the four (4) Operational Modes available in our system:

    1. Powered, Oil-fired FHW “conventional” heating only.
    2. Powered, Oil and Wood-fired dual fuel heating.
    3. Powered Wood-fired heating only.
    4. Powerless Wood-fired heating.

    Powered, Oil-fired FHW “conventional” heating mode is conventional in all regards. There is an “open on rise” aquastat (adjustable) on the wood boiler that performs two (2) functions:

    1. Inhibits the oil burner boiler primary control when the wood boiler temperature setting is reached.
    2. Opens a motorized valve to enable the inter-boiler convection loop to operate.
      “Set it and forget it” applies.

    Powered, Oil and Wood-fired dual fuel heating is enabled when the wood boiler aquastat engages and disengages the oil burner and the convection loop valve as wood burning proceeds. There is a second aquastat on the wood boiler supply pipe that “closes on rise” as water temperature approaches the boiling point (set at 200F). It opens a zone valve that initiates a second close-coupled convective loop allowing room temperature (or above) water in the “Hot Roc” Tank to temper the boiler water temperature. So if you overfill the wood boiler and walk away there is no consequence. Works beautifully! This feature is referred to as a “Dumping Zone” – getting rid of the excess energy.

    Powered Wood-fired heating only operation is similar to the oil and wood mode excepting the oil burner is fully disabled by moving the wood boiler aquastat to its lowest setting nearing ambient room (and therefore water) temperature. We have another option on our particular oil burner primary control of a built-in switch-off feature. (A common switch could also be employed to open this wood boiler aquastat to primary control circuit.)

    Powerless Wood-fired heating is merely emulating the operation of the powered mode while adjusting FloChek Valves on your heating zones and maintaining your wood boiler temperature range. In fact you can strike a boiler charging pattern that can free you from full-time babysitting the “dragon”. Our Samson 5D (Expansion Slug Type) Boiler Controller will maintain a temperature setting reasonably well on the Old National excepting when you seriously overcharge the beast — then things start happening! When the pipes start banging you have to “expeditiously” open the “Dump Zone” Tank Valve manually to temper it down. You learn this lesson in a hurry!

    To summarize, we used the wood only mode (powered and powerless) continuously for nine (9) consecutive years, providing full-home corner to corner heating and providing our domestic hot water for our large family. (The summer season requires a little lifestyle scheduling.) Annual wood consumption was four (4) to four and a half (4-1/2) cords per year.

    Since that time our lifestyle changes have precluded wood-only operation, but it’s there if we need it. Evidencing a severe ice storm a couple years ago that crippled most of New England for over a week, it was a mere inconvenience to us.

    Unfortunately gravity convection heating has little applicability to the current external wood boiler rage. They require electrical power for operation. The internal wood boiler is another matter, such as is employed in our case. Hopefully some of our experience can be used in configuring your system or trimming a little operating cost from it.

    Author’s Update: 05/12/2017

    We have incorporated our gravity heating experience into what we believe to be the first, practical, efficient and affordable Pre-built “Delta-T ECM Hydronic (FHW) Heating APPLIANCE”. Non-Provisional Intelligent Property (Utility Patent) Protection is in process in the USA & Canada. Check it out at www.BoilersOnDemand.com.