ELECTRIC RADIANT FLOORS

ELECTRIC RADIANT FLOORS

Electric radiant floors typically consist of electric cables built into the floor. Systems that feature mats of electrically conductive plastic mounted on the subfloor below a floor covering such as tile are also available.

Because of the relatively high cost of electricity, electric radiant floors are usually only cost-effective if they include a significant thermal mass such as a thick concrete floor and your electric utility company offers time-of-use rates. Time-of-use rates allow you to "charge" the concrete floor with heat during off-peak hours (approximately 9 p.m. to 6 a.m.). If the floor's thermal mass is large enough, the heat stored in it will keep the house comfortable for eight to ten hours without any further electrical input, particularly when daytime temperatures are significantly warmer than nighttime temperatures. This saves a considerable number of energy dollars compared to heating at peak electric rates during the day.

Despite its name

Despite its name, radiant floor heating depends heavily on convection, the natural circulation of heat within a room as air warmed by the floor rises. Radiant floor heating systems are significantly different from the radiant panels used in walls and ceilings. For this reason, the following sections discuss radiant floor heat and radiant panels separately.

RADIANT FLOOR HEAT

There are three types of radiant floor heat -- radiant air floors (air is the heat-carrying medium), electric radiant floors, and hot water (hydronic) radiant floors. You can further categorize these types by installation. Those that make use of the large thermal mass of a concrete slab floor or lightweight concrete over a wooden subfloor are called "wet installations,” and those in which the installer "sandwiches" the radiant floor tubing between two layers of plywood or attaches the tubing under the finished floor or subfloor are called "dry installations."

Radiant heating

Radiant heating systems supply heat directly to the floor or to panels in the wall or ceiling of a house. The systems depend largely on radiant heat transfer -- the delivery of heat directly from the hot surface to the people and objects in the room via infrared radiation. Radiant heating is the effect you feel when you can feel the warmth of a hot stovetop element from across the room. When radiant heating is located in the floor, it is often called radiant floor heating or simply floor heating.

Radiant heating has a number of advantages. It is more efficient than baseboard heating and usually more efficient than forced-air heating because it eliminates duct losses. People with allergies often prefer radiant heat because it doesn’t distribute allergens like forced air systems can. Hydronic (liquid-based) systems use little electricity, a benefit for homes off the power grid or in areas with high electricity prices. Hydronic systems can use a wide variety of energy sources to heat the liquid, including standard gas- or oil-fired boilers, wood-fired boilers, solar water heaters, or a combination of these sources.

CONTROL SYSTEMS

CONTROL SYSTEMS

All types of electric resistance heating are controlled through some type of thermostat. Baseboard heaters often use a line-voltage thermostat (the thermostat directly controls the power supplied to the heating device), while other devices use low-voltage thermostats (the thermostat uses a relay to turn the device on and off). Line-voltage thermostats can be built into the baseboard heater, but then they often don't sense the room temperature accurately. It's best to instead use a remote line-voltage or low-voltage thermostat installed on an interior wall. Both line-voltage and low-voltage thermostats are available asprogrammable thermostats for automatically setting back the temperature at night or while you're away.

Baseboard heaters supply heat to each room individually, so they are ideally suited to zone heating, which involves heating the occupied rooms in your home while allowing unoccupied area (such as empty guest rooms or seldom-used rooms) to remain cooler. Zone heating can produce energy savings of more than 20% compared to heating both occupied and unoccupied areas of your house.

Zone heating is most effective when the cooler portions of your home are insulated from the heated portions, allowing the different zones to truly operate independently. Note that the cooler parts of your home still need to be heated to well above freezing to avoid freezing pipes

Some storage systems

Some storage systems attempt to use the ground underneath homes for thermal storage of heat from electric resistance cables. However, this requires painstaking installation of insulation underneath concrete slabs and all around the heating elements to minimize major heat losses to the earth. Ground storage also makes it difficult for thermostats to control indoor temperatures.

Any type of energy storage systems suffers some energy loss. If you intend to pursue an electric thermal storage system, it would be best for the system to be located within the conditioned space of your home, so that any heat lost from the system actually heats your home, rather than escaping to the outdoors. It would also be best to know how quickly heat will escape from the system. A system that leaks too much heat could cause control problems, such as the accidental overheating of your home

Baseboard heaters

Baseboard heaters should sit at least three-quarters of an inch (1.9 centimeters) above the floor or carpet. This is to allow the cooler air on the floor to flow under and through the radiator fins so it can be heated. The heater should also fit tightly to the wall to prevent the warm air from convecting behind it and streaking the wall with dust particles.

The quality of baseboard heaters varies considerably. Cheaper models can be noisy and often give poor temperature control. Look for labels from Underwriter's Laboratories (UL) and the National Electrical Manufacturer's Association (NEMA). Compare warranties of the different models you are considering.

ELECTRIC WALL HEATERS

Electric wall heaters consist of an electric element with a reflector behind it to reflect heat into the room and usually a fan to move air through the heater. They are usually installed on interior walls because installing them in an exterior wall makes that wall difficult to insulate.

ELECTRIC BASEBOARD HEATERS

ELECTRIC BASEBOARD HEATERS

Electric baseboard heaters are zonal heaters controlled by thermostats located within each room. Baseboard heaters contain electric heating elements encased in metal pipes. The pipes, surrounded by aluminum fins to aid heat transfer, run the length of the baseboard heater's housing, or cabinet. As air within the heater is warmed, it rises into the room, and cooler air is drawn into the bottom of the heater. Some heat is also radiated from the pipe, fins, and housing.

Baseboard heaters are usually installed underneath windows. There, the heater's rising warm air counteracts falling cool air from the cold window glass. Baseboard heaters are seldom located on interior walls because standard heating practice is to supply heat at the home's perimeter, where the greatest heat loss occurs.

ELECTRIC FURNACES

ELECTRIC FURNACES

Electric furnaces are more expensive to operate than other electric resistance systems because of their duct heat losses and the extra energy required to distribute the heated air throughout your home (which is common for any heating system that uses ducts for distribution). Heated air is delivered throughout the home through supply ducts and returned to the furnace through return ducts. If these ducts run through unheated areas, they lose some of their heat through air leakage as well as heat radiation and convection from the duct's surface.

Blowers (large fans) in electric furnaces move air over a group of three to seven electric resistance coils, called elements, each of which are typically rated at five kilowatts. The furnace's heating elements activate in stages to avoid overloading the home's electrical system. A built-in thermostat called a limit controller prevents overheating. This limit controller may shut the furnace off if the blower fails or if a dirty filter is blocking the airflow.

ELECTRIC THERMAL STORAGE

ELECTRIC THERMAL STORAGE

Some electric utilities structure their rates in a way similar to telephone companies and charge more for electricity during the day and less at night. They do this in an attempt to reduce their "peak" demand.

If you are a customer of such a utility, you may be able to benefit from a heating system that stores electric heat during nighttime hours when rates are lower. This is called an electric thermal storage heater, and while it does not save energy, it can save you money because you can take advantage of these lower rates.

The most common type of electric thermal storage heater is a resistance heater with elements encased in heat-storing ceramic. Central furnaces incorporating ceramic block are also available, although they are not as common as room heaters. Storing electrically heated hot water in an insulated storage tank is another thermal storage option

compared

compared with electric resistance heating. The exception is in dry climates with either hot or mixed (hot and cold) temperatures (these climates are found in the non-coastal, non-mountainous part of California; the southern tip of Nevada; the southwest corner of Utah; southern and western Arizona; southern and eastern New Mexico; the southeast corner of Colorado; and western Texas). For these dry climates, there are so few heating days that the high cost of heating is not economically significant.

Electric resistance heating may also make sense for a home addition if it is not practical to extend the existing heating system to supply heat to the new addition.

System limits

System limits Heat pump data is taken from tests according to EN14511, therefore the head losses from heat source fans or liquid pumps are taken into account in the heat capacity and COP data. This model also includes the heat sink liquid pump.
The model takes into account the net space heating demand, Lh, of the house. The heat demand of the house is a consequence of the choice of the load profile and the so-called system losses Lsys. The size of Lsys depends on the characteristics of the boiler and the installation characteristics. The system losses include fluctuation losses, stratification losses, distribution losses, buffer losses and timer losses, which are set as a percentage that is depending on the heat demand.  
The model also includes losses from control, auxiliary equipment and system buffer standing losses.  
A back up heater is used to cover up the energy demand that the heat pump cannot deliver.  
The electricity use in the model is accounted with the primary energy factor 2.5

Input to the calculations

Input to the calculations The test method for testing the heat pump refers to best testing practice e.g. EN 14511 (see document 7) except for some deviations. The test points are similar to the test points in EN14511:2007, but the temperatures of the return/feed temperature differs, se table IV.2 in the standard. In LOT 1 the temperature difference between Treturn and Tfeed gets larger the higher temperature of the Tfeed. Only three test points are necessary to calculate the seasonal energy efficiency by using this model.  
The calculation uses a temperature bin method to evaluate the seasonal energy efficiency, etas. There are three different climates to chose among, warmer (+2°C), average (-10°C) and colder (-22°C), see table I.1, LOT 10.  Each bin describes the equivalent number of hours corresponding to the bin temperature with a resolution of one bin/K. Input data

The maximum heating capacity,

The maximum heating capacity, Pmax, at the different climates is calculated from the heating capacity data obtained in the test. It is not possible to choose the size of the required heat load for the building, but is given by the model for each bin level based on the capacity of the heat pump. To meet the lower heat load requirements at the different bin levels, the heat pump is assumed to work in part load condition. The heat pump does not have to be tested in part load operation; instead the model uses a degradation factor, Cd, to calculate the COP when working in part load condition. Cd can either be obtained from tests or a default value, Cd=0.15, can be use

For fixed capacity units

For fixed capacity units the default is COPmin= 0.89*COP at power output Phpmin=0.5*Php. For staged capacity units the default is COPmin= 0.975*COP at power output Phpmin=0.5*Php.  For variable capacity units the default is COPmin= COP at power output Phpmin=0.4*Php.
It is optional to choose whether the heat pump operates with night set back or not. The bin assumes constant night temperatures during night set back to +1°C, +6°C and 0°C for each climate respectively.  
Other inputs to the calculations is type of heat pump, type of operation of the heat pump, type of control of the heat pump, type of heating (floor heating or radiator heating), minimum source operating temperature, the effect of auxiliary equipment and backup electricity heater.  
Other possible energy sources can also be chosen, but this chapter only treats the heat pumps.