Geothermal Pump
The goal of this project is to find an environmentally friendly, cost effective, consumer pleasing means to heat and cool a normal home, as well as provide water heating capabilities.
The objective of the HVAC team is to design a heating and cooling system that has a very high level of efficiency, and is incredibly effective at generating an environment that is considered comfortable by the occupants of the buildings. In designing the system to meet this criteria, it is the goal of this team, when practical, to harness devices that function primarily in one of the HVAC sub-systems and use them in other subsystems. This results in a truly innovative and integrated HVAC system that is even more efficient because single devices serve multiple roles.
The key factors of comfort that were considered are temperature, humidity, and air pollutants (see Air Quality Team). Early in the research stage it became evident that the HVAC system for The Home Depot Smart Home could be separated into three different subsystems. The first, energy conversion, includes not only the conventionally used energy sources such as oil, natural gas, and electricity, but also geothermal, solar, and wind (convection) energy sources. The second, energy storage, includes hot water tanks and thermal masses. The final subsystem is energy transport which includes radiant floor heating, water as a carrier, air as a carrier, and the use of dampers to control the areas targeted for heating or cooling. After an extensive review of the available devices for each of the subsystems and investigating ways that certain devices could serve multiple subsystems, a final framework for HVAC system was formulated. This framework is summarized in this abstract.
The energy conversion subsystem will be comprised of a geothermal heat pump (primary) and will also draw from solar energy sources for thermal masses and wind (pressure gradients) to ventilate the building under certain conditions. In addition to providing heating and cooling for the building, the geothermal heat pump will also be used to generate hot water. This is made possible by running a water loop between a hot water tank and the compressors within the geothermal heat pump unit to collect the waste heat off the compressors. Hot water will also be generated by a solar hot water heater located on the roof of the building that will feed the hot water tank.
This hot water tank makes up part of the energy storage subsystem. The hot water tank will have the capability to generate hot water through conventional methods, however, it is predicted that the number of conventional heating events will be minimal due to the additional devices that will be providing hot water. The other component of the energy storage subsystem is the use of thermal masses. The success of this part of the subsystem depends upon the geometry and architectural design of the building. These materials need to be placed such that in the winter they absorb solar radiation and in the summer they remain in the shade and do not absorb energy.
With regards to the third subsystem, energy transport, it is the recommendation of this team that multiple methods should be employed. This will provide numerous opportunities for future research focusing on the efficiency and effectiveness of the systems in the building. The two methods chosen are air as the medium and radiant floor heating which circulates water through loops in the floor. The radiant floor heating will be primarily supplied by the geothermal heat pump, however it will also, during heating mode, use the solar hot water heater and Thermal masses as energy sources. By running a set of loops through Thermal masses, the absorbed energy in the material can be moved to other areas of the building. The air system will be directed by dampers which will provide the ability to heat (or cool) different zones to various levels.
At present, it is the determination of this design group that a 7 ton geothermal heat pump unit manufactured and installed by TRANE best fits the needs of The Home Depot Smart Home. Geothermal heat pumps operate using the principle that the ground temperature below the frost line remains at nearly constant temperature throughout the year. The heat pump uses the differences between the this constant temperature and the temperature within the building to either transfer energy from the house to the ground (cooling mode) or transfer energy from the ground to the building (heating mode). The TRANE unit chosen combines a true geothermal heat pump with a conventional system. The entire unit is reported to be three times as efficient as a full conventional system of similar capacity. In addition to being made efficient by the geothermal loop, the TRANE unit’s efficiency is increased by having multiple compressors so that it can effectively meet different load requirements. Another important characteristic of the TRANE geothermal heat pump is that waste heat from the compressors can be used to heat water which can then be stored in a hot water tank for use in showers and dishwashers. If possible, a horizontal loop system should be used instead of a vertical loop due to the inaccessibility of the vertical loop once it has been installed.
In addition to the three subsystems that for the HVAC system for The Home Depot Smart Home, there is in reality a fourth subsystem which is still in the conceptual phase of design. This subsystem refers to the control of the HVAC system. The concept of this subsystem is to develop a logic whereby the central computer for the building evaluates the environmental conditions in each of the rooms as well as the outdoors and makes decisions as to the movement and circulation of the different volumes of air. The building would have the ability to open windows, close shades, and also move air effectively.
In order to successfully meet the objectives of the building with regards to efficient energy use, the architectural design must be created with these systems in mind. This team believes that it is an incorrect approach to design the building first and then fit systems to the house. Because the success of many of these systems depends on the orientation and geometry of the building, ignoring these factors may result in rendering certain systems ineffective. This team believes that the correct approach is to design a building that is itself an energy efficient system rather than one that contains systems that are efficient. This distinction may appear to be subtle, however, failing to recognize the differences can result in the loss of major opportunities.
The success of passive solar and wind (used for ventilation and cooling) are dependent on the design of the building to be effective systems.