Overview of Integrated Renewable Energy Systems
Integrated renewable energy systems are the combination of technologies which augment one another in order to maximize system performance and energy savings that cannot be realized with individual systems. EEC's showcase home provides an example of integrated systems and their potential energy savings. It incorporates several technologies, including solar hot water, geothermal heat pumps (GHPs) , hydronic radiant distribution, and a 6 KW solar PV array. These integrated GHPs work in conjunction to provide space conditioning and hot water for the entire home, and the solar PV provides enough electricity to offset power use by the HVAC systems. In addition, an energy recovery ventilator (ERV) helps maintain high indoor air quality by refreshing indoor air while minimizing energy loss.
These systems are integrated and designed with the building envelope and features of a low energy home in mind. As a result, this home uses approximately 80% less energy than a similar sized home built with standard construction practices. Integrated systems can be incorporated in both existing and new homes to provide 60-70% energy savings. See our page on costs and benefits for examples of representative pricing and potential cost savings.
In combination with a quality building envelope, integrated systems offer a huge energy and greenhouse gas savings potential for the residential buildings sector. For more examples of the system design features and advanced technologies that Energy Environmental Corporation implements in its integrated systems, please visit our corporate website.
Heating and Hot Water
The integrated GHP system in EEC's showcase home combines solar hot water collectors and a geothermal heat pump to produce 100% of hot water demand for radiant hydronic heating and domestic hot water (DHW). The solar hot water panels are oversized to provide 90% of hot water demand through EEC's unique staged solar design. A water-to-water GHP augments the solar hot water system when necessary to maintain a constant temperature in the hot water storage tanks. This can also be done with a water to air GHP with a desuperheater. These temperatures are monitored and controlled by set points on temperature sensors. Because the water is already pre heated by the energy from the sun, the GHP runs at partial loads, which uses 60% less energy than when running at peak loads. As a result, energy use is minimized while the efficiency of the heat pump is maximized. Furthermore, the excess heat produced by the oversized solar hot water panels during the summer months is redirected to the ground loop. This warms the ground and entering water temperature of the GHP which can increase the efficiency of the heat pump in the early heating season. Preheating the ground with solar is referred to as solar assisted GHP. Heat for the home is then distributed through a high mass radiant distribution system, which provides comfort while avoiding drafts and ductwork heat losses associated with forced air heating.
Hydronic Radiant Cooling
Hydronic radiant cooling with reversible water-to-water GHP is the most cost effective way to heat and cool a home. It avoids the need and associated costs for a second water-to-air GHP unit and ductwork for forced air cooling. Heat absorbed by the floor is circulated to a desuperheater built into the GHP to simultaneously cool the home and produce hot water. The GHP consumes far less energy than a central forced air system, and domestic hot water is free during the summer. One drawback is the potential for condensation and resulting mold. However, in a semi arid climates, this can be avoided simply by incorporating a real time dew point sensor and controls.
Passive Radiant Cooling
The high mass radiant slab is coupled with the geothermal ground loop, so that when the ground loop temperature is cooler than the floor temperature, the home can be passively cooled without the use of the GHP compressor. Instead, direct heat exchange will take place between the ground loop and hydronic floor using a low energy circulation pump. Since compressors consume 73% of the energy of a GHP system, and circulation pumps only consume 11%, passive cooling provides significant energy savings.
See our radiant heating and cooling section for more information about the controls being incorporated into the home..
Indoor Air Quality
Indoor air quality (IAQ) is a major problem associated with homes in the US. 96.7% of North American homes have at least 1 of 6 common IAQ problems. The most common indoor air problem is particle allergens such as dust, dander, pollen, spores, and bacteria, which occur in 91% of all homes. High IAQ in the platinum LEED home is the result of a water-to-air GHP running in conjunction with an energy recovery ventilator. GHPs involve no combustion, thereby avoiding fumes and pollution associated with some forms of conventional systems. The ERV incorporates HEPA filtration and will provide regular air exchanges and humidity control with minimal energy use. As a result, there is little or no indoor air pollution and reduced allergens.
Platinum LEED Home Integrated System Design
Below is a graphical representation of the integrated systems in EEC's showcase home. The solar PV array is not included in the diagram.
Click HERE to see a large version.
Energy Efficiency of Integrated GHPs
The systems in EEC's showcase home have been designed to be undersized (3 ton GHP) according to the heating and cooling load calculations. During periods of peak load demand, electric resistance heating in the air ducts will augment the heating system. As a result, installation costs are reduced, and the systems consume far less energy. This is reflected in the table below which shows the results of a modeling analysis by EEC comparing an integrated system design with several applications of stand alone GHP systems. Calculations were performed using the Vela Solaris Polysun integrated systems software.
| GHP Design | Annual Operating Cost | Total DHW Cost | Average COP (SPF) | Annual GHP Heating Energy Use (Kwh) | Annual GHP Cooling Energy Use (Kwh) |
|---|---|---|---|---|---|
| Integrated GHP: 3 ton W-W with solar assist |
$675 |
$219 |
4.05 |
4011 |
868 |
| Single GHP: 3 ton W-W |
$1026 |
$315 |
3.49 |
6318 |
868 |
| Single GHP: 3 ton W-A |
$975 |
$327 |
3.65 |
6075 |
793 |
| Average Home single GHP: 4 ton W-W |
$1528 |
$519 |
3.38 |
8625 |
1705 |
| Average Home single GHP: 4 ton W-A |
$1245 |
$272 |
3.47 |
8423 |
1552 |
W-W: water-to-water geothermal heat pump
W-A: water-to air geothermal heat pump
SPF: The average coefficient of performance (COP)
Comparison of the annual operation costs of a 3 ton versus 4 ton W-W GHP system shows that the 3 ton system consumes far less energy, reflected in cost savings of $706 annually. Integrating a 3 ton GHP with solar collectors reduces energy consumption by 30%, cost savings of $447 annually, and an increase in the COP of the system by 16% compared to a stand alone 3 ton W-W GHP. This is in addition to the 50% energy savings that a stand alone GHP can provide when replacing conventional natural gas heating/hot water and central air cooling systems.
By monitoring the flow rates, water temperature, and energy use with sensors and controls in real time, the COP and energy savings can be maximized. As an example, a recent study found that performance optimization of flow rates on the load side of a geothermal heat pump resulted in an increase of the COP for heating by 6.8% and improve cooling capacity by 8%.
Summary of Energy Efficient Design Features
The following summarizes the design, components, and optimization techniques implemented by EEC which help to increase the performance and energy savings of platinum LEED home integrated systems. We estimate that energy efficiency of the systems are 70-80% greater than conventional HVAC systems by using the following technologies and features:
- Heating water primarily with solar hot water collectors, augmented by water-to-water GHP running at partial loads.
- Dual stage GHP compressor operating at 60% of the rated energy when running under partial load conditions.
- Microprocessor-controlled GHPs equipped with variable speed ECM2 motors for water-air configurations.
- Water flow and temperature sensors to calculate COP during GHP operation and optimize system performance in real time.
- Reversible GHPs that provide comfortable radiant floor cooling with real-time dew point control to eliminate condensation potential.
- Soft start compressors to reduce start-up current loads.
- Solar thermal-assisted heating to the ground loop prior to the heating season to increase COPs by increasing entering water temperature (EWT).
- Outstanding indoor air quality and efficiency created by over sizing return air ducts (for water-air GHP).
- MERV 8 filtration on the GHP with integrated Energy Recovery Ventilators (ERVs) incorporating HEPA bypass filtration.
