Recently introduced ABB HygienicMaster electromagnetic meters are playing an important role in the highly instrumented residence of Amory Lovins, cofounder of Rocky Mountain Institute. This non-profit organization drives the efficient and restorative use of resources. One area of its many efforts is the study of advanced energy efficiency in buildings.
Lovins's private residence, located at an elevation of 7100 feet in the Rockies, serves to develop and demonstrate many earth-friendly architectural concepts. Built in the early 1980s, the superinsulated building remains highly energy-efficient. It depends primarily on passive systems, despite its extreme location. The technologies and design strategies used then are even more effective, affordable, and readily available today.
Until recently the building included an unconnected radiant floor heating system installed in its concrete floor slabs. During construction, the relatively inexpensive installation of six zones of hydronic tubing served as a future backup heating source. Meanwhile two wood-fired stoves provided supplemental heat when the passive systems could not meet demands, which happened every winter. In 2008, Lovins decided to try eliminating the wood stoves by connecting the hydronic tubing in the slabs to an expansion of the existing active-solar water-heating system.
The building now uses a hybrid system of passive- and active-solar heat sources coupled with thermal storage, and backed up by renewable electricity, to provide domestic hot water and hydronic radiant floor heating. The system favors solar heating, with the electric boiler operating only when thermal storage falls short. Three integrated components work together to create the building’s warmed water: a closed solar-thermal loop, a closed radiant floor loop, and an open domestic hot water (DHW) loop.
Seven ABB FEH300 HygienicMaster electromagnetic flowmeters serve in these new loops. One measures flowrate of a glycol/water mixture in the solar-thermal loop that includes a 1500-gallon stratified storage tank. Four measure flow to the radiant heating floor zones. A sixth measures the return flow from the floor zones undergoing reheating in the storage tank. The final ABB magmeter measures open loop water flow to the building's domestic hot water tank. Data from these and roughly 190 other sensors will help researchers optimize the building's energy efficiency.
To provide heat for the new load required by the radiant floor system, engineers doubled the number of SunEarth solar hot-water panels from four to eight. The solar-thermal system, contains a 40/60 glycol/water with flowrates measured by an ABB Hygienic electromagnetic meter. The glycol/water mixture provides the necessary balance between freeze-resistance and pumping efficiency.
The fluid travels through insulated copper pipe from the panels to the 1500-gallon storage tank, located below the master bedroom closet. Within the tank, 50 ft of corrugated stainless steel coil serves to exchange heat from the glycol mixture to the tank’s water. The stratified storage tank acts like a thermal battery.
When the fluid temperature at the exit of the solar-thermal panels is 15F˚ hotter than the top of the storage tank, the pump turns on to deliver heat from the panels to the tank. The pump shuts down when the top of the tank reaches 180˚F. The solar check valve prevents thermosiphoning. If the panels get too hot, the system sends an email alert to have them shaded to prevent boiling of the fluid. An emergency heat dump has also been programmed to pull heat out of the storage tank and into the floor slabs to prevent panel overheating. (This aspect is still being refined and may be combined with a new controlled mixing valve.)
Radiant Floor and Electric DHW System
An integrated closed system connects the solar hot water storage tank, an electric backupboiler, the floor heating zones, and the domestic hot water tank. The fluid is plain water to optimize energy efficiency.
The tank for domestic hot water has priority. If it's not hot enough, the radiant floor pump will stop feeding the floor zones until the temperature of the DHW tank water rises sufficiently. The DHW pump connects the electric boiler with the DHW tank. The two pumps operate independently, pumping in opposite directions.
A thermostat in each of the radiant floor zones controls a solenoid valve. When the thermostat calls for heat, the low-energy solenoid opens a full-port ball valve. The Grundfos Alpha2 pump activates upon sensing the resulting pressure drop, providing heat to the loop. By responding to pressure requirements in real time, this single hydronic circulation pump controls the hydronic flow for each of the six zones, rather than requiring a secondary pump for each zone. Four ABB Hygienic (stainless steel) electromagnetic flowmeters monitor the flow to floor zones. Lovins designed the hydronic piping for such low friction—with fatter pipes, no or sweet bends, and diagonal (nonorthoginal) layout—that a maximum of 42 watts of pumping power replaces the normal requirement of more than a kilowatt.
When a floor zone calls for heat, several components determine how the water circulates. The solenoid valve shown usually remains closed. In this case the cool circulating water from the floor zones splits between the cold intake of the mixing valve (C) and the loop through the solar storage tank.
Depending on the temperature of the returning water and the setpoint temperature of the mixing valve, either no water will pass through C, or some percentage will. The difference between the combined four meters to the zones and the meter measuring the return from the storage tank is the amount of fluid hot enough for the mixing valve to let pass. The remainder of the cool water must flow back through the solar-heated storage tank. This water passes through a heat-exchange loop within the tank and then returns to the hot-water intake of the mixing valve (H). Another ABB Hygienic magmeter monitors the flow to the through this loop.
The mixing valve controls the temperature of the water passing through it by mixing cold and hot water. In the case of a large demand from the radiant floors, the returning water will be cold. If so, most of the water will not pass through the cold intake, and instead be routed through the solar storage tank to gather more heat. The mixing valve will pass only enough return water through its cold intake to make the outflowing water the desired temperature, determined by the its dialed setting. (This mixing valve should soon be replaced with an electronically controlled mixing valve to further optimize performance.)
If the radiant floor calls for only a small amount of heat (if, for example, only one small zone is turned on), the returning water may still be quite warm. In this case, a smaller amount of water will divert to be re-heated in the solar storage tank. Back at the mixing valve, the warm return water will balance the outflow to the desired temperature setting.
After passing through the mixing valve, the water enters the electric boiler. It cannot flow through the domestic hot water tank because the DHW pump acts as a closed valve when it's not operating. The boiler senses the temperature of the incoming water and will fire to maintain a temperature of 100˚F. The boiler won't fire if the incoming water from the solar storage tank is sufficiently hot. The water passes through the boiler to be delivered to the zone calling for heat, and the cycle repeats. The electric boiler is powered by onsite photovoltaic or utility windpower, and is expected to run rarely.
The case of an open solenoid valve will be rare, resulting from an extended period of cloudy winter weather. If the temperature of the water at the top of the solar heated tank falls below 80˚F, the hydronic floor loop won't pick up sufficient heat. So the solenoid opens and bypasses the loop running through the solar storage tank, directing the cool return water from the floor zones directly to the electric boiler.
Domestic hot water
The primary heating source for the DHW tank is solar. A 900 sq ft central atrium called the Greenhouse serves as the "furnace" for the building. This space, combined with heat gain from windows, lights, appliances, and people, generally provides all the heat needed for the entire building. The heat is stored in the masonry, the floor, the water, and the earth under the house. Because of the building's huge thermal capacity, heat storage lasts for months. Heat captured in September may be used in December.
Municipal cold water enters the building from the west wing. Before passing through any active heating elements, the water runs through 100 meters of tubing within the upper section of the south-facing Greenhouse arch. By passing through this large solar-heated thermal mass, the water gets a free boost in temperature. After passing through the greenhouse arch, the water flows through a dedicated heat exchanger in the top of the solar storage tank, and proceeds to fill up the DHW tank. An ABB Hygienic magmeter monitors water flowrates to the DHW tank.
If the DHW tank cools off from disuse for an extended period of time, the pump will energize and circulate the water back through the solar storage tank for reheating. This will happen if the temperature at the top of the DHW tank is less than 120˚F and the water at the top of the solar storage tank is greater than 135˚F. Otherwise the electric boiler of Figure 2 will supply the necesary heat from all-renewable power.
The electric boiler connection to the DHW tank is a low priority heat source. An aquastat mounted to the DHW tank measures the water temperature in the center of the tank. If it falls below 112˚F, the DHW pump activates and circulates the closed loop through the electric boiler, raising the temperature.
The savings generated by all the measures taken to conserve energy are significant. In the mid-1980s, Lovins's measurements showed savings around 99 percent of space- and water-heating energy, 90 percent of household electricity, and 50+ percent of household water. With early 1980s technologies, the resulting $19-a-day energy savings repaid the extra cost of the efficient equipment in the first ten months of the building's operation. In the past few years, the 1983-vintage technologies have all been updated by a quarter-century to 2009 state-of-the-art. Lovins looks forward to commissioning the industrial-strength monitoring software so he can tell how much more efficient the newer technologies are. But meanwhile, he confirms that the ABB Hygienic magmeters—which he chose for their accuracy and their lack of flow resistance and moving parts—have been a key to setting up the unusual active-solar and hydronic systems and fine-tuning their controls for maximum system efficiency.