A great article about Hydronic Floor Systems from PMEngineer’s 2013 Flooring Guide:
Comfort and economy of operation are linked with
well-designed and properly installed hydronic radiant floor systems.
Providing thermal comfort by transferring energy from point-of-source to point-of-use in hydronic (water-based) systems is achieved by a wide variety of radiant-floor installation methods and each requires varying degrees of water temperature to deliver the same results. The radiant floor temperature boundary for human comfort revolves around maintaining a floor surface temperature below 85° F.
The human body loses heat in four basic ways: radiantly (your body radiates heat); convectively (air currents); conductively (direct contact — barefoot on an unheated tile floor); and perspiration (latent heat of evaporation). Skin surface temperature averages 85°. A floor surface temperature above 85° upsets the balance between the four and will cause people to be uncomfortably warm.
A general misconception about radiant floor warming is that the 85° design limitation was required to protect hardwood flooring. If that was true, hardwood floors heated to well above 100° while baking in direct
solar gain would be easily and permanently damaged!
Radiant floors are often a perfect marriage with all types of hardwood floor coverings and all available floor surface materials are compatible with hydronic radiant heating. Modern hydronic radiant design programs provide the system designer with the ability to “install” virtually any type of floor covering over the radiant floor panel, which provides an ability to determine compatibility and the required water delivery temperatures to offset the heat loss.
It is not unusual for room-by-room designs to require a wide variety of water delivery temperatures. Numerous reliable methods are available to precisely control multiple- temperature delivery from a single-temperature source or from blended systems where multiple- and varying-temperature energy sources are incorporated.
Comfort and economy of operation are inexorably linked with well-designed and installed hydronic radiant floor systems. Low-temperature designs offer
the greatest opportunity to blend a wide variety of energy sources, maintain peak operating efficiencies (especially true for geothermal or air-to-water heat pumps), and to incorporate alternative energy sources such as wind, solar photovoltaic and solar thermal. The lower the system’s temperature requirements, the better the overall system-wide efficiency, which will ensure the lowest possible operating costs for fuel and power.
The majority of hydronic radiant systems, certainly the better-designed ones, will employ a control strategy that will alter water temperature based upon whatever Mother Nature is giving us outside. The building’s heat loss will be greater as outdoor air temperatures fall. Conversely, system water delivery temperature will be increased
to transport more comfort-energy to the radiant floors — the colder it gets outdoors, the hotter the water.
How hot depends on the installation method used for the floors, the materials between the radiant tubing and/or panels and the room served, the desired
20 RADIANT FLOORING GUIDE
temperature of the room, and the insulation below the radiant tubing/panels that directs radiant energy toward the conditioned space.
CONSTRUCTION/DESIGN METHODS
When designing or considering installation methods, system delivery temperatures will vary widely. In order to provide thermal comfort, offset the heat loss of the space being served, conserve energy, stay within consumers’ budgets and use heat sources effectively. Limiting floor surface temperatures to a maximum of 85° ensures comfort.
The illustration on page 20 depicts a variety of installation methods and their corresponding required water delivery temperature where the floor surface temperature must equal 80° on a design day in order to provide sufficient thermal comfort.
RETROFIT AND ADDITIONS
A large market exists for adding hydronic radiant floors to existing homes where steam, hot water baseboard or even hot air systems exist. A number of manufacturers provide add-a-zone prebuilt hydronic radiant control panels that incorporate everything
required except for the installation of the radiant floor components.
FLOOR WARMING
High-density tile and stone products feel cold (conduction) to bare feet and the human body can sense heat loss (radiant) to the high-mass flooring products
Imagine the joy of stepping onto a warmed bathroom floor in summer and/or winter and then discover it can be a reality instead of just a dream. Floor-warming systems are typically controlled via programmed cycles so the floor is heated only as desired.
CONTROL STRATEGIES, ENERGY CONSERVATION
If the existing heating system in the home is water-based, then heated water is available but most likely not at the correct temperature. Once the radiant system’s design and installation method is chosen, any primary hot water source can be tapped into and adjusted in the radiant zone’s mixing strategy — from simplistic mixing valves to more advanced injection mixing.
Electrically commutated motor circulators can dramatically reduce electrical power consumption by 80%
or more. Low-wattage zone valves can be incorporated to complete the energy conservation picture.
If the existing system is air-based, older low-efficiency furnaces can be upgraded by the addition of a hydro-coil or replaced with a hydro-air furnace. Existing water heaters can be replaced with ultra-efficient indirect water heaters or by boilers with a built-in domestic hot water generation system.
BEYOND COMFORT
Homeowners today want to know what Energy Conservation Value the installed hydronic system will provide and how it relates to the return on investment.
ECV is the amount of energy conserved at today’s utility rates when compared to an existing appliance and/or new appliances. The entire system from energy source
to energy transportation to radiant panel construction determines the real-world performance and efficiency.
Hydronic radiant heating equals healthy heating, too. Indoor air quality is enhanced, homes are easier to keep clean, drafts are not created, germs have fewer places to hide and people get sick less often.