• Tag Archives Hot Water
  • HEATING A CHURCH – Warming Up The Congregation

    Heating a church is seemingly always a challenge. Whether it’s the structure’s physical attributes, the climate variations, the occupancy schedule and warmup demands, no two are alike nor can they be treated as such.

    Oh, to turn back the clock a few centuries when most churches including the Great Cathedrals of Europe were unheated! Shivering through a lengthy sermon must have certainly tested the faithful. However, we have become sensitive to our comfort in modern times including group participation in religious activity. “Passing the plate” to pay the fuel (heating or cooling) bill is particularly noteworthy to the congregation and usually a topic of comment.

    The scope of our discussion will be limited to and focus upon improved heating of a church (or similar structure) via enhanced air handling. In our experience most congregations have focused on cooling enhancement by adding ceiling cooling fans and employ them to more aggressively circulate air with or without air conditioning. Now revisit a church during the heating cycle ….. and the fans are still! Why?

    Heated air warms people, and eventually the structure. Seat yourself on a cold pew bench or metal chair when it seems that the air around you is reasonably warm and you will get the message. Add the practice of doing temperature setbacks between occupancy to conserve fuel (customary in churches and meeting places) and you aggravate the warmup process. Some of this can be alleviated with the use of Programmable and WiFi Thermostats, but even these cannot address the underlying issues of efficient heated air distribution, our topic.

    As simple and as obvious as it may seem, heated air rises! Any contained structure, heated or unheated, exhibits a higher temperature at its top vs. its base. Whether it’s a fully “vaulted” cathedral or an arctic igloo, the effect is measurable. No complaints from the choir loft in a cathedral, by the way! An extreme can be found in a high-bay warehouse where seasonal upper temperatures can reach above 140°F, an immediate personnel health endangerment. It must therefore become obvious that we must turn on the fan(s) to advantage the heating situation, but how and when?

    Virtually all structures employ perimeter heating, i.e. placement of heating radiation or air registers around the exterior walls and usually somewhat positioned under windows where feasible. Heating radiation and heated air registers induce “convection” or natural rising and circulation of heated air and diffusing it with the cold air emanating from windows and exterior walls to eliminate their cooling effects. This heated and “mixed” air rises toward the centered ceiling or higher “cathedral ceiling” area creating natural convection and diffusion. Depending upon the individual structure attributes and aggressiveness of the radiation delivery there is always a level of lamination at the center/peak that can be advantaged by forcing it downward to mix and accelerate the heating process. The following pictorial is offered:

    Figures 1 & 2 above depict natural temperature lamination and convective flow of a perimeter-heated structure.

    Heating elements are purposefully placed against lower exterior walls to induce thermal convection while diffusing (mixing) with cooler air off the exterior walls for greater comfort. However, lighter heated air rises and accumulates at the ceiling levels, stratifying the air mass above. Cooling uppermost air gradually sinks and diffuses with lower, forming a midway convective path as depicted. Natural convection is never complete and the structure’s air mass is always significantly graduated temperature-wise from bottom to top.  The “vaulted” or “cathedral” ceiling in Figure 2 accentuates this condition, as coloring depicts. We must use forced convection (blowers or fans) to advantage ourselves.

    Our contention can be readily proven by switching on your present summer cooling fan(s), rotating to force air downward and adjusting until a modest air movement is felt. Turn on your heating thermostat and you will note a significantly quicker time-to-temperature resultant. The initially laminated air mass is diffused and then mixes with newly heated air to approach a more uniformly heated air mass. Ideally you should leave the fans on during the occupancy period, irregardless of thermostat demand cycling. It should be obvious that if circulation as described is not attainable, fan resizing and positioning may be necessary.

    Fan operation should be integrated into the heating system to maximize utilization and efficiency. The techniques must differ to suit each basic system type.

    1. Boiler-based Forced Hot Water (Hydronic) or Steam Systems are relatively simple to integrate. Trace the supply line from the top of the boiler outlet to the radiators or baseboard in the fan-located heating area.

    a. Place a heat-sensing “strap on”, “close on rise” aquastat such as the appropriate Honeywell 4006, 6006 Series on this supply line. Re-wire the power feed to the fans through the aquastat.

    b. Set the aquastat at 120°F as a starting point. Adjust in operation to suit. The lower the set point the longer pre-heat and post-heat fan operation to initially diffuse and then maintain comfort levels during cycling.

    2. HVAC Systems require a little more sophistication. Consult with a qualified technician to ascertain the proper strategy for lowering and lengthening system air delivery rates and timing.

    Note that an alternative control method is using a kick-space heater thermostat to switch a power relay such as a Honeywell RA89A (or other). Unfortunately the kick-space thermostats are typically available only in 110ºF (Low Option) 0r 130°F (Standard). However they can also be directly wired into an HVAC System, depending upon type. Commercial variants are available in different temperature settings as may be required.

    Using the prior technique another expedient is available. Purchase a common 24/7 Day Cycle Timer to dry switch the Honeywell RA89A Power Relay directly via its T-T (Thermostat) Terminals. Program the timer to approximate the 24/7 occupancy periods. Not as efficient, since intermediate heating cycles are not accommodated, but comfortable for the congregation. 

    Air lamination is an atmospheric attribute that must be addressed in all heating and cooling applications. Our scenarios apply not only to churches but assembly halls, public buildings and selective residential applications. In the end it’s cooperating with Mother Nature rather than fighting her.

     


  • DOMESTIC HOT WATER (DHW) GENERATION – YOUR OPTIONS

    We just returned from a hardship “no heat” service call. These folks are obviously up against it economically, as are many these days. However they recently substituted an electric water heater for their boiler immersion coil to generate domestic hot water and hopefully reduce their summer fuel bill. Now they are concerned about the increase in their electric bill as a consequence.

    This brings up the timely subject of options available in DHW generation. Please refer to content in our other blogs, specifically related to energy source selection, tempering tanks and using a Heating Cost Calculator. For the latter we use the NH OEP Heating Cost Calculator at http://www.nhclimateaudit.org/calculators.php. There should be equivalent calculation tools available for your region.

    Heating Cost Calculators don’t lie. They provide a unit energy cost per Million BTU’s for each fuel. You should apply an appropriate AFUE (Energy Efficiency Rating) for your or the best competing appliance by fuel type to get an accurate comparison.

    By calculation DHW heating fuels from lowest to highest costs are: (NH Region)

    1. Natural Gas – Rate factored by 1.5 to 2 for actual billing. (Divide total fuel billing by actual fuel charge for factoring.)
    2. Fuel Oil
    3. Propane
    4. Electricity – Must be also factored for actual billing. Ours is 1.85. (Varies significantly by Provider & Region)

    Note: 1&4 are “distributed fuels”, necessarily incurring varied pipeline and distribution service costs.

    Natural Gas has been historically the most efficient fuel for both heating and DHW generation vs. fuel oil until recently. A very rough crossover is a $45/bbl Crude Oil Price. Local fuel market variations and appliance installation costs must be considered. Propane, a manufactured fuel, is by comparison a significantly higher cost product. This is unfortunate in that they utilize the same appliances (with minor modification) with similar efficiencies. Propane fuel cost is a killer!

    Fuel Oil and Gas Heating Appliances provide the same function, however differing significantly in configuration to accommodate their particular combustion characteristics.

    Electricity despite its extremely high energy efficiency is offset dramatically by unit cost. Electric Water Heaters are enticingly priced, too. Too bad.

    We are considering only the intermittent combustion fuels (oil and gases) in our analysis. The continuous combustion fuels such as wood, coal, etc. suffer by nature to being very inefficient DHW generators. This is not to allow that these fuels fired in boilers can provide seasonal DHW to Indirect Storage Heaters or coupled to a central boiler with an immersion coil. Although increasing in rural popularity, they don’t represent a significant market segment to date, nor likely will they ever.

    Gas and Oil Combustion Appliances are limited to Boilers and Water Heaters. Their configuration options are similar with the exception of the Gas “Demand” Water Heater and are as follows:

    1. A “stand-alone” (dedicated) Oil or Gas Water Heater. These are a virtual necessity when the central heating appliance is Forced Hot Air (FHA). The stand-alone Oil-fired Hot Water Heater has suffered from poorer fuel efficiency by design and has been limited to high demand users such as restaurants, etc.
    2. The Gas “Demand” Water Heater – A unique, hang-on-the-wall device, it stores no heated water but fires only when DHW flow demand is detected. It is very sensitive to water conditions, including acidity, contamination and lower delivery temperatures.
    3. A Central Heating Boiler with an Immersion Coil therein to create DHW.
    4. A Central Heating-only Boiler coupled to an Indirect Water Heater (Super-insulated DHW Storage Tank). Provides higher efficiency in both heating and DHW generation. Significantly increasing in popularity.

    The Gas-fired “On-Demand” Water Heater has a distinct DHW market application, subject to several limitations:

    1. They are “pricey” relative to other options.
    2. Initial DHW delivery is mildly delayed during warm up.
    3. Long cycle demand capacity reduces with supply water temperature decrease (colder water from source).
    4. Annual chemical treatment to control sedimentation is required to maintain performance.

    Note: Both the Gas “On-Demand” Water Heater and Boiler Immersion Coil Systems mentioned can benefit from a “Tempering Tank” placed in line with their water supplies. (Reference our prior blog on these.) It’s a non-insulated accumulation tank that allows water to acclimate to ambient (room) temperature before entering the DHW heating device. Increases heater performance significantly by temperature and delivery maintenance over total cycle demands.

    Otherwise, Indirect Storage Heaters are the path to efficient DHW generation and storage – regardless! They compliment lifestyle variations and usage patterns when coupled to an efficient heating-water-only generating device, commonly referred to as a “Cold Start” Boiler. It fires ONLY when area heating or DHW recovery is demanded. Otherwise they revert toward ambient temperature, saving significant “standby losses” when not in use. There are several options to “getting there from here”, depending upon your situation.

    1. Purchase a High-efficiency “Heat-only” Boiler and Indirect Water Heater as a package and be done with it.
    2. You can convert your existing Immersion Coil System Boiler to a “Cold Start” Type by:
      • Changing your Master Aquastat Control to a “Cold Start” Unit
      • Adding an Indirect Water Heater with its own circulator or valved zone.
    3. Couple an Insulated DHW Storage Tank to your current Boiler Immersion Coil with a POTABLE WATER CIRCULATOR ONLY (Stainless or Bronze) and Temp Aquastat Zone in the loop. Substitute a “Cold Start” Master Aquastat to convert your boiler to a “Heat-only” as in Option 2.
    4. Do Item 3, but convert a good 80 Gal. Electric Hot Water Heater into a Storage Tank. Strip its wiring and utilize the upper, internal Thermostat Switch as a DHW temp control. Note: This last option is the “Cheap Trick”. It costs significantly less to install, despite the pricey circulator requirement. DHW piping is typically run in parallel with the immersion coil with a flow check function.

    Whenever employing ANY Storage Tank for DHW, place a Thermal Expansion Tank in-line on the cold water supply line! Heating cold water expands it, creating pressures well above the supply pressure and potentially bursting the system. This is particularly evident in municipal or well supplies where there’s a check valve in the cold water service. Cheap insurance!

    So, using the appropriate fuel costs from a Heating Cost Calculator and reviewing your current or planned appliances, plan your Heating and DHW Systems together for best efficiency.

    Last Edit: 06/24/2017 pdm


  • ADVANTAGES OF A TWO-TEMPERATURE DHW (DOMESTIC HOT WATER) SYSTEM

    Legally, Plumbing & Heating Technicians are required to set the DHW (Domestic Hot Water) temperature at a maximum of 120 Degrees Fahrenheit at the faucet(s) (taps). The purpose is simple, to prevent personal injury particularly of children and when operating any water tap. It works, but is it ideal for the residential or commercial user? No.

    Like any regulation it has up and down sides. The down side is that some dedicated appliances need higher water temperatures or you pay it back in poorer performance and increased electrical energy costs. Dishwashers and commercial power washers are the primary examples.

    Commercial Dishwashers require a continuous 140 Degrees Fahrenheit supply to assure bacterial elimination and augment the sanitation cycle (electrical enhancement). We have had more than a few instances where clients have not been able to meet State Health Dept. Guidelines. In all cases there was a misapplication of DHW heating equipment involved. Shouldn’t a similar situation exist with residential DHW generation? It does.

    Examples:

    1. Local Dealer installed a Rinnai Demand Water Heater to supply a commercial dishwasher in a restaurant. Rinnai and others supply up to a 120 Degree F output as shipped. There is an internal switch to increase this to 140 Degrees F — and immediately void your Warrantee. There is a product application disclaimer on these and other Demand Heaters specifically excluding commercial dishwashers and other similar applications. Moreover they will not supply the volume of water over time (the Delta-T Problem). The only potential solution is to supply tempered water to the heater (see other blogs), but this can be iffy even for this application.
    2. Area Church installed a gas-fired 40 gallon water heater to supply their commercial dishwasher. Even if you could force the temp up to 140, there is not enough stored and resupply volume to operate through cycle(s). Being a single DHW source in a public structure, then what do you then do about tap water temperatures?

    Now, what about your residential dishwasher? The same process applies with similar results — but you don’t see it readily. That 120 Degree F (at best) water does its thing, but not as efficiently. Your initial wash temperature is low and efficiency suffers. The electricity-sucking water temp coil and sanitizing cycles are notorious energy users. (Look at the Wattage Data on the Appliance Nameplate.)

    The obvious solution in all cases is to supply hotter water to all dishwashers. In one manner or another you must provide a dual temperature source to accomplish this. The techniques vary depending upon your DHW source:

    1. Electric, Gas&Oil-fired and Indirect DHW Heaters – Increase your thermal switch or aquastat temps up to 140 Degrees F (the usual max allowable by design). Then separate your piping to the dishwasher (and other?) and install a good quality Tempering Valve into your other tap water supply line(s).
    2. Immersion (Tankless) DHW Coil in your Boiler – Ideal situation. Tee the output of your coil to dishwasher (and other?) for maximum temperature water. Careful – it is scalding hot!
    3. Provide a separate, high temperature & capacity DHW Heater to suit the particular appliance(s).

    Meanwhile do the “cheap tricks”:

    1. Insulate all your DHW lines from heater to use points, regardless and inasmuch as possible.
    2. Shut off your DHW immersion coil boilers between cycles to save energy during low heating season demands. It only takes about 15 minutes to reheat. Plan ahead.
    3. Open the nearest hot water tap to your dishwasher (kitchen sink?) to get water hot before cycling your dishwasher. This will minimize that initial wash temperature problem in the dishwasher.

    If you should decide to employ high temperature DHW taps for specialized use, do it safely. Secure them!

    Last Edit: 10/10/2012 pdm