1. Field of the Invention
This invention relates to hydronic space heating and cooling systems used in heating, ventilating and air conditioning systems for residential and commercial buildings.
2. Description of Related Art
Heating, ventilating and air conditioning (HVAC) systems for residential and commercial buildings, use many systems for adding or removing heat from a confined space in order to control the ambient conditions in the space. One such system uses a centralized heat addition or removal system to heat or cool a distribution liquid such as water which is then circulated through a supply conduit to the space of concern. The distribution liquid is then routed to an appropriate heat exchanger and the ambient air of the space which is in thermal connection with the heat exchanger is either heated or cooled to maintain the desired conditions in the space. On exiting the heat exchanger, the distribution liquid is recirculated through a return conduit to the centralized heat addition or removal system.
The hydronic distribution system thus described is typically referred to as a "two pipe" system because the heat exchanger has one supply conduit and one return conduit. When this system is applied to multiple heat exchangers, each located in a separate air conditioning zone, simultaneous heating of one zone and cooling of another zone is not possible. An alternate system called the "four pipe" system uses two centralized units, one for cooling a distribution liquid and one for heating a distribution liquid. The chilled and heated liquids are both routed to the heat exchanger through separate supply and return lines and valves are used to admit either chilled or heated liquid to the heat exchanger depending on ambient conditions in the zone. In this manner, one zone can be in heating mode while another is in cooling mode.
The existing HVAC systems utilizing hydronic distribution are well documented in the American Society of Heating, Refrigeration and Air Conditioning Engineers 1987 ASHRAE HANDBOOK Volume for Systems and Applications. Generally, the hydronic distribution systems fall into one of two categories, all water systems or air and water systems. All water systems are characterized by the entire heating or cooling load of the space being carried by the water distributed to the heat exchanger apparatus in the space of concern. Air and water systems distribute both water and air to the space of concern. The water and air are heated or cooled and share in the heat load of the space.
Both of these systems require circulation of water or some other liquid to a heat exchanger in each of the spaces of concern. The heat exchangers used in a building are typically fan coil units containing a finned heat transfer coil, a fan and an air filter. The number of heat exchangers used in a building is dependent on the heating and cooling load and the need to control the heating or cooling in one space or zone independently of other spaces or zones.
In HVAC design it is generally desirable to have as many independently controlled zones as is economically feasible. Having multiple, independently controlled zones allows adjustment of ambient conditions in one zone to suit the occupants without impacting conditions in another zone. In addition, multi-zone systems can maintain uniform conditions throughout a building in spite of variations in the heating or cooling loads between zones caused by differences in thermal insulation, or the quantity of heat generating appliances or occupants in a zone. Also, multi- zone systems are energy efficient because the heating or cooling load for zones which are not in use can be easily isolated. Although more zones improve the performance and efficiency of the HVAC system, they also raise the cost A major component of this increased cost is the material and labor associated with the hydronic distribution system. Each zone must have a heat exchanger requiring a liquid piping system which will convey sufficient quantities of heated or chilled water to accommodate the heating or cooling load. Typically these piping systems use threaded, galvanized, steel pipe or sweat fit, copper tubing.
Installation of these piping systems is labor intensive. Manufactured steel and copper piping or tubing come in straight runs and fittings for accommodating turns and curves. Each connection of a straight run with a fitting requires a joint either threaded or sweat fitted, solder connected. A substantial amount of installation labor is involved in making each joint. For threaded connections, first the pipe must be cut to the appropriate length and then the threads must be cut on the end of the pipe using a pipe threading dye. Next the threads must be dressed, cleaned and coated with a sealing compound or a "TEFLON" tape to prevent leaks. Finally, the connector must be screwed to the pipe end with sufficient thread contact to prevent leaks. In the case of sweat fit solder joints, the labor is comparable in that the tubing must be cut to the proper length, the end of the tubing must be dressed and the then joint must be heated to the proper temperature with a torch to effect a satisfactory solder joint.
Another difficulty with installing these typical systems is that sufficient space must be allocated for the straight runs of piping or tubing in the initial design of the structure. In residential buildings, piping is usually run in the crawl space under the structure. In larger, typically commercial buildings, pipe chases or runs are allocated for running pipes or wiring. In either case, the rigid piping requires hangers or supports spaced between two and five feet apart to adequately support the piping.
In addition to the difficulty in installing these piping systems, there is a substantial problem of maintaining them. As is well known, joints in a piping system are more susceptible to leaks than are the continuous runs of piping materials. Consequently, more joints in a piping system contribute significantly to the additional cost of checking a system for leaks in pre acceptance testing and in maintaining a system after it is installed. Another maintenance problem associated with rigid, metal piping is corrosion caused by oxidation or galvanic action. Corrosion of steel or copper piping causes leaks in the hydronic system which are often located in inaccessible locations requiring time consuming and difficult repair.
Still another problem with rigid piping systems is that they are susceptible to freeze damage during severe weather. If the temperature of the air surrounding the piping drops below the freeze point and there is insufficient flow of water through the piping, the water will freeze and expand until the pipe is split.
It is an object of this invention to reduce the cost of multi- zone HVAC systems used in residential and commercial buildings
It is another object of the invention to provide an easily installed hydronic distribution system for multi-zone HVAC systems.
It is another object of the invention to provide a hydronic distribution system which requires minimum maintenance.
It is yet another object of the present invention to provide a hydronic distribution system which is corrosion resistant and more tolerant of freezing conditions than is rigid, metal piping or tubing.