Summary
This chapter has covered the more common hydronic systems used in air- conditioning buildings.
Natural Convection and Low Temperature Radiation Heating Systems The very simplest water heating systems consist of pipes with hot water flowing through them. The output from a bare pipe is generally too low to be effective, so an extended surface is used to dissipate more heat. The radiator emits heat by both radiation and convection. These water heaters can all be controlled by varying the water flow or by varying the water supply temperature.
These hydronic heating systems do not provide any ventilation air from out- side. When water systems are in use, ventilation requirements can be met by opening windows, window air conditioners, or separate ventilation systems with optional cooling.
Panel Heating and Cooling
Radiant floors use the floor surface for heating. Ceilings can also be used for heating and/or cooling. The system has the advantage of taking up no floor or wall space and it collects no more dirt than a normal ceiling.
Fan Coils
Fan coils can be used for just heating or for both heating and cooling. When the fan-coil is used for heating, the hot water normally runs through the unit continuously. Some heat is emitted by natural convention, even when the fan
is off. When the thermostat switches the fan on, full output is achieved. Some units are provided with two, or three speed controls for the fan, allowing adjustment in output of heat and generated noise. Types of fan coils include: Hot-water fan coils, changeover systems, and four-pipe systems.
Two Pipe Induction Systems
The two-pipe induction system uses ventilation air at medium pressure to entrain room air across a coil that either heats or cools. The units are typically installed under a window, and when the air system is turned off, the unit will provide some heat by natural convection if hot water is flowing through the coil.
Water Source Heat Pumps
Water source heat pumps are refrigeration units that can either pump heat from water into the zone or extract heat from the zone and reject it into water. This ability finds two particular uses in building air conditioning:
1. The use of heat from the ground
2. The transfer of heat around a building.
Bibliography
1. ASHRAE 2000 Systems and Equipment Handbook
2. ASHRAE 2001 Fundamentals Handbook