RADIANT HEATING SYSTEMS

RADIANT HEATING SYSTEMS

Radiant heating systems typically combine a central boiler, water heater or heat pump water heater with piping, to transport steam or hot water into the living area. Heating is delivered to the rooms in the home via radiators or radiant floor systems, such as radiant slabs or underfloor piping.

Advantages of radiant heating systems include:

·         Quieter operation than heating systems that use forced-air blowers.

·         Increased personal comfort at lower air temperatures. The higher radiant temperatures of the radiators or floors allow people to feel warmer at lower air temperatures. Some homeowners, with radiant heating systems, report being comfortable at room air temperatures of 60°F.

·         Better zoning of heat delivered to each room.

·         Increased comfort from the heat. Many homeowners, with radiant heating systems, find that the heating is more comfortable.

Disadvantages of radiant heating systems include:

·         Higher installation costs. Radiant systems typically cost 40% to 60% more to install than comparable forced-air heating systems.

·         No provision for cooling the home. The cost of a radiant heating system, combined with central cooling, would be difficult to justify economically. Some designers of two-story homes have specified radiant heating systems on the bottom floor and forced-air heating and cooling on the second floor.

·         No filtering of the air. Since the air is not cycled between the system and the house, there is no

filtering of the air.

·         Difficulty in locating parts. A choice of dealers may be limited.

HEAT PUMP EQUIPMENT

Heat pumps are designed to move heat from one fluid to another. The fluid inside the home is air and the fluid outside is either air (air-source), or water (geothermal). In the summer, heat from the inside air is moved to the outside fluid. In the winter, heat is taken from the outside fluid and moved to the inside air.

AIR-SOURCE HEAT PUMPS

The most common type of heat pump is the air-source heat pump. Most heat pumps operate at least twice as efficiently as conventional electric resistance heating systems in Climate Zone 4. They have typical lifetimes of 15 years, compared to 20 years for most furnaces.

Heat pumps use the vapor compression cycle to move heat (see Figure 7-2). A reversing valve allows the heat pump to work automatically in either heating or cooling mode. The heating process is:

1.       The compressor (in the outside unit) pressurizes the refrigerant, which is piped inside.

2.       The hot gas enters the inside condensing coil. Room air passes over the coil and is heated. The refrigerant cools and condenses.

3.       The refrigerant, now a pressurized liquid, flows outside to a throttling valve where it expands to become a cool, low pressure liquid.

4.       The outdoor evaporator coil, which serves as the condenser in the cooling process, uses outside air to boil the cold, liquid refrigerant into a gas. This step completes the cycle.

5.       If the outdoor air is so cold that the heat pump cannot adequately heat the home, electric resistance strip heaters usually provide supplemental heating.

Periodically in winter, the heat pump must switch to a "defrost cycle," which melts any ice that has formed on the outdoor coil. Packaged systems and room units use the above components in a single box.

At outside temperatures of 25°F to 35°F, a properly sized heat pump can no longer meet the entire heating load of the home. The temperature at which a properly sized heat pump can no longer meet the heating load is called the balance point. To provide supplemental backup heat, many builders use electric resistance coils called strip heaters. The strip heaters, located in the air-handling unit, are much more expensive to operate than the heat pump itself. The strip heaters should not be oversized, as they can drive up the peak load requirements of the local electric utility.

A staged, heat pump thermostat can be used in concert with multistage strip heaters to minimize strip heat operation. To overcome this problem, some houses use a dual-fuel system that heats the home with natural gas or propane when temperatures drop below the balance point.

Air-source heat pumps should have outdoor thermostats, which prevent operation of the strip heaters at temperatures above 35°F or 40°F. Many mechanical and energy codes require controls to prevent strip heater operation during weather when the heat pump alone can provide adequate heating.

The proper airflow across the coil is essential for the efficient operation of a heat pump. During installation, the airflow rate must be checked to ensure that it meets the manufacturer’s recommendations

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