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Hydronic Radiant Heat
Energy Efficiency, Comfort, and Health
When engineered and installed correctly, hydronic radiant heat can be very effective at making a home feel comfortable since it heats the occupants directly and relies less on the indirect heat transfer of moving warmed air. When it is combined with a home’s water heater or boiler, total system efficiency increases and total home energy usage decreases, since it saves energy by reducing standby loss and reclaiming the heat of the hot water coming back from the return loop. These efficiency gains of a combined hydronic system (making double use of water heating equipment) can also be attained by using a hydronic air handler (instead of a furnace) in conjunction with a well designed air duct system.
Radiant systems should typically be installed in conjunction with a ventilation system to avoid stagnant air issues; this is because radiant heat does not provide for indoor air circulation, filtration, or ventilation.One way to address this is to combine a hydronic radiant heat system with mechanical ventilation such as a Heat/Energy Recovery Ventilator (HRV or ERV) to provide for a low energy exchange of stale indoor air with fresh outdoor air .
Function and Optimal Operation
A hydronic radiant heating system provides centrally controlled heating to a home and is most easily engineered for a new home installation. In some cases, it is possible to retrofit existing homes with radiant floors and baseboards. For other situations, it may be more appropriate to use radiant heat only in certain rooms and in conjunction with a traditional or hydronic forced air system. In addition, it can be configured to integrate renewable technologies such as solar thermal water heating, provided there is a “summer heat dump” like a swimming pool to prevent overheating in warmer months when space heating needs are minimal. Homes that require Air Conditioning, and don’t have room for typical ductwork must use alternatives to typical central air conditioners, such as ductless mini-split A/C, high velocity ducted systems, or even radiant cooling if the cooling load is small enough.
Highest efficiency levels will be attained when used in conjunction with a zoning system with multiple thermostats; this leads to cost savings due to not having to heat the entire house at all times, as well as increased comfort in rooms which tend to be warmer or cooler than the rest of the house.
There are two main categories of radiant heating:
- Radiant Floors
- Radiant Baseboards
There are three types of radiant floor systems and all are most effective when installed under hard floor surfaces such as wood, concrete or tile, as they are relatively good conductors of heat. Radiant floor systems can be designed to operate with some forms of carpeting, but are not as efficient and have a greater lag time in temperature adjustments. The varieties are:
- High Mass: integrated (wet pour) or stapled down with gypcrete or concrete
- Low Mass: Thermalboard™ or warmboard™ sleeper systems installed above the sub floor
- Staple up: installed with heat transfer plates directly below the sub-floor, most commonly used in retrofitting applications
Care must be taken when designing radiant floor systems to ensure compatibility with the use patterns, heat source, flooring type, and design strategy of the building.
Components
Water Heater or Boiler | Thermostat and Controls | Circulation Pump | Heating Coils or Radiators
These systems must be designed and installed by experienced and licensed contractors as there are many components that must work together to maximize safety, performance and efficiency. Each component plays an important role in the functioning of the system and can have a significant impact on the total system efficiency.
Water Heater or Boiler
These provide the heat and hot water to make the home comfortable. Either may be used to integrate space heating and domestic hot water into a combined hydronic system:
- Boilers can be integrated into a combined hydronic system with the addition of an indirect fired tank
- Hot water heaters can be integrated into combined hydronic system with the use of a heat exchange system to protect the domestic hot water.
There are many factors to consider when choosing between heating sources including:
- Home’s heating load
- Occupants domestic hot water needs
- Heating degree days (how much and how extreme is typical for cold weather)
- Cost of materials and labor
- Fuel Costs
- Possible integration with a solar hot water system
The efficiency of the heating source will deliver comfort and efficiency to the system only if these factors are considered carefully and if the distribution system is well designed and installed. Boilers and water heaters which are capable of modulation, where heat output is electronically matched to need, can achieve efficiencies of 95%. [+] MORE
Thermostat and Controls
This is the main point of interaction an occupant has with the systems which regulate the temperature and air quality of the living spaces. Whether the heat is delivered through a forced air or radiant heating system, thermostats and more sophisticated controls can allow the occupant to interact with the air regulation systems to tailor and automate temperature as well as humidity and ventilation. By using zoned thermostats and pumps (or zone valves) to break up a home into separately controlled segments (zoning), you save money by not having to heat the entire house and are able to vary comfort levels throughout the home. However, the energy efficiency and comfort levels attainable with a programmable or zoned thermostat are limited by the efficiency of the radiant heating system it controls, as well as the building envelope of the home in which it operates. In addition, for radiant systems using a large thermal mass to store heat, setbacks with programmable thermostats are not optimal because of the long response time (the mass takes awhile to warm up again once it has cooled down). [+] MORE
Circulation Pump
This propels the hot water through the system to the hydronic loops in the living space and back to the water heater or boiler. New variable variable speed pumps use electronic controls to modulate speed of the pump to regulate the amount of heat being delivered throughout the house, leading to greater comfort and efficiency compared to fixed speed pumps.
Heating Coils or Radiators
Hot water flows to these apparatuses (which can be under floor coils or baseboard radiators) where heat radiates out to the room. Baseboard radiators create a very gentle convective current in the room (the air movement is imperceptible compared to a forced air system) in addition to the direct radiant heat. Radiant floors use primarily use radiant heat to directly heat the people, floors and furniture in the room, instead of relying on the indirect heat transfer of blowing air from forced air systems.