SENV 7006
Case Study
Indoor Air Quality
The materials used in the building
Agrifiber is used to reduce the emission of pollutant into the air. Agrifiber, a rapidly renewable and regionally sourced material, was used for door cores. Composite wood and Agrifiber products (MDF, particleboard, plywood, wheatboard, strawboard, panel substrates, door cores) used in interior of building shall contain no added urea formaldehyde resins.（http://www.greenexamacademy.com/eq4-4/）
sandblasted hard-troweled concrete finish: Sandblast finishes can leave basic gray concrete with a sandstone texture disguising brush marks. The concrete will not emission chemical gas and it will absorb the air and bleed water in the building. （http://www.nrmca.org/aboutconcrete/cips/20p.pdf）
Fig1. The materials uesd in the building （http://www.nrmca.org/aboutconcrete/cips/20p.pdf）
Geothermal System
The geothermal well field uses the earth’s constant temperature to offset heating and cooling loads and it is closed-loop geothermal system which will avoid the affluents entering the building through operation.
Fig2. Geothermal System（http://www.nrmca.org/aboutconcrete/cips/20p.pdf）
Heat pump system
Heat pump efficiency strategies: 1-stage high efficiency water to air heat pump, 2-stage hig efficiency water to air heat pump, water to water ground source heat pump and well field and VFDs for system pumps
During the winter and fall seasons, southern and northern zones may have different cooling and heating demands. Heat pump systems are ideal under simultaneous heating and cooling conditions as the loop water allows for rejecting heat absorbed from the southern zones to the northern zones.
The heat pump utilized in the IUB/OCA building are served from a horizontal geothermal well field west of the building. Such a system is commonly referred to as geothermal heat pump system. The horizontal closed loop well field contains U-shaped piping where pairs of pipe in each bore hole are connected to manifolds in a geo vault. The 645 feet long geothermal loop is the longest known Horizontal Direct Drilling (HDD) geothermal loop ever installed in the United States. [2]
Window
Significant north and south glazing elements. Light tuba skylights to allow deeper daylight penetration. South glazing has exterior shading devices. Minimal east and west glazing.
Window to floor area ratio:18.3％ ; window to wall area ratio: 34.6％.Iowa’s climate is heating dominant and therefore typically higher solar heat gains are desired. Unlike most commercial office buildings, the building has operable windows to enhance occupant comfort and satisfaction as well as potentially improve indoor air quality. Use of the windows is tightly controlled and the staff is notified via email when the outside conditions are again notified to close the windows when the outside conditions deteriorate or at the end of the working day. Although it may be possible to lower the energy consumption associated with mechanical ventilation with operable windows, they are mostly a feature to enrich occupant satisfaction. The individual zone level heat pumps are automatically shut down when the associated operable windows are open, but developing a relevant performance metric or quantifying energy savings attributable to these operable windows could be very complicated. [2]
The windows were specified as operable to utilize natural ventilation. The building automation system identifies favorable exterior conditions, sending an email to occupants when windows should be opened and closed. The automation system shuts down the associated zone’s heat pumps when windows are opened, ensuring energy is not wasted. These windows are also installed within 15 feet of 53% of the interior spaces to maximize the use of natural daylight. [2]
Others
Fan and pump strategies: premium efficiency supply/return fan motors and premium efficiency pump motors.
Conditioning of outside air strategies:
Demand controlled ventilation, underfloor air delivery system, room-level heating/cooling setpoints equal to 70/74℉, four-day/10- hour per day work week, and total heat recovery.
CO2 monitoring and control :
lowering ventilation levels and window characteristics. Schedule changes and varying the building’s temperature settings are conceptually straightforward and do not require the addition of new technologies.
Underfloor air distribution system(UFAD)
It provides the conditioned air via a series of channels or ductwork, terminal units and diffusers installed within a raised floor system. A UFAD can improve a mechanical system’s overall ventilation effectiveness and normally allows operation with higher cooling temperatures and lower heating temperatures; however, often space constraints and restrictions prevent it from being a viable alternative and energy savings can often be overstated. More research is being done to fully determine the effciency of this system type. [2]
Varying the thermostatic setpoint and setbcak temperatures,Operating nder a four-day, 10- hour per day work week, Utilizing a total heat recovery unit
ASHRAE standard 62.1 provides the basis of determining the appropriate ventilation rates for when the building is occupied. A building can be occupied but a certain room or space might only experience periodic usage. Providing ventilation air based on CO2 levels can offer significant energy savings by allowing the ventilation system to operate intermittently instead of continuously.
There are two basic types of air-to-air energy recovery units typically utilized in building HVAC systems. A heat recovery ventilator(HRV) usually refers to a device that transfers sensible heat or energy from the exhaust air stream to the supply air stream. The heat transfer raises the incoming outdoor air temperature in the winter and lowers it in the summer. A total energy recovery ventilator(ERV) is a device that can transfer both sensible and latent heat between air streams and allows for some moisture to be exchanged, potentially raising the humidity of the incoming outdoor air in the winter and lowering it during the summer. [2]
Utilizing an energy recovery ventilation can have significant implications on the operational costs of the HVAC system. Mechanical humidification is energy intensive and requires an additional 1100 Btu/lb of energy to change phase to increase the airstream humidity and generally requires overcooling the supply air to wring the excessive moisture out but may result in the need for reheating it. The ERV is a cost effective means of conditioning the outdoor air to provide better indoor air quality and lower energy and operational costs.
The selected design feature a 6000 CFM total energy recovery ventilator with a design specified 62% summer effectiveness and 68% winter effectiveness. [2]
Fig3. Operable Window. [1]
Fig4. Total Energy Recovery Ventilator. [1]
The final system design does not include an underfloor air distribution. The total heat recovery ventilator represents the second largest energy cost savings potential of all the energy efficient strategies examined and the CO2 control was the third largest in terms of potential energy cost savings.
Building automation system
The CO2 level are monitored and recorded by the system, there are two categories include the CO2 emission situation, the meeting room CO2 levels and the meeting room occupancy. By recording energy end use at the circuit level, aggregated energy consumption of the CO2 level can be calculated. The key energy and indoor-air quality related data allows detailed evaluation of subsystem performance and helps with the investigation of any operation problems. The data can also be used to calculate actual sub-system performance metrics which can then be compared with design parameters or specifications. [2]