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  • HYDRONIC (FHW) HEATING OPTIMIZED – “Going Back To Nature?”

    A primary tenet of Industrial Engineering is: To properly justify a process change you first optimize the existing process, then define the proposed process and make your CBA’s (Cost-Benefit-Analyses) for both. From weighing these you will then derive your best course of action. Speaking from painful experience as a Manufacturing Process Engineer, you will make this mistake only once. Somewhere in a dark corner of a semiconductor facility (or hopefully a scrap pile) lies my personal ill-advised, sophisticated process equipment humiliation!

    The makings of similar embarrassments are appearing within the hydronics heating industry. Hydronic component suppliers can be placed into three primary groups: boiler, distribution and radiation providers. They correspond to the three basic elements of the hydronic heating process. Component suppliers define the scope and applications of their products within a heating system, but that’s all. History and physics now become excellent teachers.

     A century ago there were two competing water-based energy heating methods, Gravity Hot Water and Steam. Both were based upon the natural (gravitational) convection attribute of water in the liquid or the vapor state, respectively. Energy distribution from a boiler to radiation required no external energy, only variation of the fuel supply ….. more heat, more fuel. Powered burners and thermostats were added for control. Pumps (circulators) doomed gravity water by adding zone management while reducing costs. Thus the modern hydronic heating system evolved.

    I’ve had the benefit of “playing with pipes”, beginning as a teenager within our family heating business for over 65 years while pursuing a paralleled hi-tech engineering career. (You can’t raise ten kids even on an engineering day job.) So while doing hydronic work “on the side”, so to speak, hydronic evolution followed me. My “engineering hat” always questioned why natural convection shouldn’t be an asset rather than a flow-checked nuisance. The old “gravities” were so simple!

    Post-engineering “non-retirement” provided time to aggressively play with hydronics. My “motor head” also makes me analogize heating systems with automobiles, i.e. the boiler being a pure “heat engine” with air, fuel and ignition for example. So when the delta-t circulator came along, there’s the “automatic transmission”. Now what can we do with the drive-line (distribution)? Can we re-evolve the Model T Ford car as a hydronic “Model Delta-T Appliance” by incorporating natural gravity convection into delta-t distribution? Well, we can and we have …..

    The old Gravity Heating System featured a large boiler, proportioned larger piping and radiation, typically all cast iron and pipe. They were skillfully defined and installed, used no distribution energy and lasted almost indefinitely, a tough act to follow. Its modern contemporary uses a much smaller (albeit more efficient) boiler, features multiple, circulated zones with smaller piping and radiation. Arguably it trades off fuel efficiency and comfort convenience for some increased distribution energy and “sophistication”.

    The sophistication referred is almost entirely within the distribution element of hydronic heating systematization.This is the consequence of a component-driven marketplace, as prior mentioned. The contemporary build-in-place method of system installations relegates hydronic interconnection of boiler to radiation in particular as “The Plumber’s Playground” wherein there are few rules and little consequence. Every system differs in a similar application, and therefore all perform differently in practice.

    If the objective is to provide overall hydronic system energy efficiency including electrical power consumption, freelancing must be both qualified and quantified in practice. Redefining near-boiler piping to optimize natural (gravity) convection with the boiler and integrating a delta-t circulator to refine hydronic delivery dramatically reduces distribution material and energy usage. Our now-patented “appliance” exhibits a typical 8 to 13 Watts total distribution energy usage while heating, over 90% reduction depending upon the contemporary configuration. Coupled with a high-mass, cast-iron boiler to enhance gravity operation, it also exhibits a thirty-plus year economic and operating life, twice or more that of low-mass, condensing units.

    Further gravity convection enhancement is available within the appliance-to-zone interconnects. The “level & square, pipes everywhere” approach does not fly in a gravity world. Minimized, pitched piping to simple series and split perimeter radiation loops are ideal. Full port valving if necessary and fewest 90° fittings further contribute to minimizing head pressures and thus distribution energy consumption. It won’t win a beauty contest, but it will win the race.

    Our 2,700 sq. ft. personally built (1970) raised ranch home has been our gravity test stand. An indoor wood boiler was convection-coupled to the cast-iron, flow-checked supply and circulator returned 3-zone “oiler” back in 1975. Multi-mode, multi-fuel operation also permitted completely unpowered, manually adjusted flow check wood gravity convection heating. As an example some years ago up here in “Frostbite Falls, NH” we were powerless from a severe ice storm for 10 days. A mere inconvenience for us ….. just feed it wood and adjust the valves.

    We currently have a series of up to six-year installed appliance “Beta Sites” that have now aggregated over twenty-five years service with no system-related calls! Two oil-contamination incidents did occur and last year a power line short-circuit blew out every control on a system. Our appliance is comprised of all standard, domestic trade components, so it was restored within the day.

    Our “appliance economics” haven’t been mentioned but are profound. Very significant complexity, material/labor content reduction and extended operating life vs. traditional architecture eclipse contemporary materials and methods. This observation was similarly but subtly affirmed in the 2019 Annual Boiler Report by several contributors opining that in effect it’s still hard to beat the economics of a well designed and installed cast iron boiler system. Their commentary and our natural (gravity) convection appliance development experience confirm that the existing, i.e. the “pre-condensing” process has yet to be optimized, to our potential peril. But try to find trade journalism and process development efforts to the contrary!

    So, is history due to repeat? That is, will a hydronic “Model Delta-T” displace this industry’s “Carriage Makers”, or will there be yet another technical “skeleton” in my closet?


    Optimization of heating efficiency first requires determining your specific requirements. In general terms there are two or more distinct heating energy uses:

    1. Area Heating – Warming occupied areas fully, or selectively as living habits occupation or use may demand.
    2. Domestic Hot Water  (DHW)– Heated, potable (drinkable) for baths, showers, laundry and personal consumption.
    3. Special Uses – High temperature power washing, sanitizing, etc. (Refer to prior blog.)

    All of these requirements can ideally be met by using a hot water boiler system as a single, central source but the question arises of how to accomplish this efficiently. Specifically, varied heating demands that may range from continuous (?) DHW to very occasional (seasonal?) and selectable area warmth can become a challenge, particularly economically. However occasional demands can “lighten your wallet” to execute and maintain. Let’s address this problem systematically.

    Arguably the most important decision has to be your heating fuel selection. We cannot overemphasize this and the use of a Heating Cost Comparator to define your choice. (See our other blogs.) The standard unit of measure is the “Cost per Million BTU” expressed as a dollar figure. We use the NH-OEP Calculator for our area usage, but similar ones are available online. Use your current or projected new heating appliance efficiencies (AFUE) to get an accurate calculation. New Gas (Natural or LP) AFUE’s are typically 95% for top end (condensing) boilers and 87% for Oil Triple-pass boilers.

    The current and foreseeable heating fuel choices have become quite obvious in the northern climates:

    1. Natural Gas (where available) is the accepted baseline. But BE CAREFUL! Natural Gas is a “distributed fuel” (through a pipeline). Your actual bill will be considerably higher due to service and distribution costs added to your actual therm usage. Get a billing estimate from your gas provider first! (Our local multiplier is up to 2.0 or 100% added for your actual natural gas billing costs.)
    2. Heating Oil is the predominant fuel where natural gas is not available.
    3. Liquid Propane (LP) Gas is another option along with oil where natural gas is not available. LP has been used predominantly for domestic cooking and somewhat for DHW generation. As an area heating and DHW fuel it has traditionally been up to a 100% premium over oil. It is a heating option of choice in our experience.

    Note that solid fuels (wool, coal, peat, waste, etc.) have been purposefully omitted from this discussion. Insurers typically disallow continuous firing fuels using interior combustion equipment. External or “outdoor boilers” are “zero pressure” and require a “plate exchanger” interface with an internal power fired system to assure continuous heating maintenance. Verify these statements and weigh potential penalties for your particular situation.

    Consumers predominantly identify their area heating options as Forced Hot Air (FHA) Furnace or Forced Hot Water (FHW) Boiler Systems. Similarly DHW options as Electric, Gas or Oil stand-alone Water Heaters or from an immersion coil within a boiler. So therefore we usually find the typical FHA System with a stand-alone DHW Heater as a combination. FHW Systems usually provide DHW from an internal Immersion Coil, as previously noted. Currently we are seeing the emergence of the Indirect Hot Water Heater, supplied by a boiler as the efficiency choice.

    But in fact our heating options are more extensive. They include:

    1. Air Handler– A FHA Furnace without a fuel-powered heating source. Instead it has an internal large radiator (heat exchanger) that is externally supplied with energy from a FHW source (boiler).
    2. Unit Heater– A radiator with fan, typically found as an overhead heater in a garage, warehouse, etc. There are also variations of these with provisions for attaching ducting – otherwise similar to an Air Handler.
    3. Plate Heat Exchanger– Basically two (or more) mutually integrated radiators allowing the interchange of heat from varied sources. Source variation attributes may be pressure, temperature, flow rate(s) and composition. Their composition may be aqueous (or not) and adjusted for properties such as freezing and/or boiling resistance.

    Utilizing these latter devices allows us to employ higher efficiency or lower cost hot water generation sources (or both) for all our area and DHW heating requirements. We respectfully suggest that where a single, efficient energy source is desirable or necessary for continuous demand a FHW boiler should be employed. Further, that this source then be applied to all your structure’s heating demands with all the resources detailed within.

    The unmentioned physical fact is that utilizing water as an energy conductor is inherently and significantly more efficient than air. Thus an HVAC System (air heating/cooling) is less efficient than a hot water boiler (heating) coupled with an air handler (cooling) combination. This can be witnessed in their assigned AFUE values.

    So, let us wrap it up by considering some common scenarios for our FHW boiler system source:

    1. A Central HVAC (Heating,Ventilation & Air Conditioning) System Upgrade.

      • Upgrade the existing FHA Furnace with an Air Handler, if desirable, or
      • Install a FHW Heat Exchanger (radiator) into an existing FHA Plenum, plumb and rewire as necessary.
      • Install a “Chiller” in the Hydronic System to provide an A/C source.
    2. Existing or planned FHA System Upgrade – Same as 1. without A/C.
    3. FHA installation into a seasonal, incremental, unheated area or as an expansion.
      • Install an Air Handler or Unit Heater variation to suit.
      • Where freezing protection is desirable, employ a Plate Heat Exchanger with anti-freeze as necessary.
    4. Use a Plate Heat Exchanger to couple “incompatible” secondary heated water sources such as exterior wood & coal boilers, solar & geothermal loops, etc.
    5. In all cases, move to an Indirect Water Heater for efficient DHW generation.

    By the way, these new high efficiency boilers do not necessarily need a chimney. Condensing Gas Boilers typically use PVC pipe for venting and Triple-Pass Oil Boilers with Pressure-fired Burners can use a direct exhausting vent kit.

    Have we run you out of options yet?

    Last Edit: 10/18/2018 pdm