SECCIÓN III POLÍTICA FINANCIERA
CAPÍTULO NOVENO TIERRA Y TERRITORIO
Fans (elec) Interior Equipment (elec) Exterior Lighting (elec) Interior Lighting (elec)
2. The heat exchangers used to transport the heat from the FCS to the building systems are 100% efficient.
3. The FCS operates constantly for all hours throughout the year. When the heat supplied by the fuel cell exceeds the heat demanded by the building, the heat is released to the environment.
Building operating schedules and the thermal and electrical demands are those specified in the DOE reference buildings. In Table A.2, typical winter and summer weeks are given for these locations. The simulations are run for an entire year and all energy calculations are performed for annual data. In addition, detailed performance profiles are examined for typical winter and summer weeks.
Table A.2. Typical Winter and Summer Weeks for the Weather Locations Used for Simulation
Location Typical Winter Week Typical Summer Week New York November 22–28 June 5–11
Boston December 22–28 July 27–August 2 Chicago January 27–February 2 August 24–30 San Francisco February 15–21 September 5–11
A.1 Air-Based Space-Heating System
As shown in Figure A.2, the small office contains five packaged single-zone air conditioners (PSZ-ACs) containing gas furnace heating coils each serving one of the five thermal zones in the building. A PSZ-AC is assembled at a factory and installed as a self-contained unit. Some types of electric packaged units are also called “direct expansion,” or DX, units. Packaged units are in contrast with the heating, ventilation, and air conditioning system in a large office that is an engineer-specified unit built up from individual components for use in a given building. PSZ-AC units are generally
mounted on the roof of the building, but sometimes are installed on a slab outside the building. Packaged units produce warm or cool air directly and distribute it throughout the building through ducts or a similar distribution system. The temperature of warm air produced by the gas furnace heating coil in the PSZ-AC and delivered to the space in the San Francisco climate is maintained between 25 and 40°C. The annual heating demand for space heating is 1390 kWh for this small office building. The average space-heating demand (when the system is operating) on a typical winter weekday is 3 kW for the small office building.
In the simulation of the small office building model in San Francisco weather, the rooftop unit supply air temperature (Supply Temperature [°C], T_supply2) in winter is maintained at 23°C by the system controller, as shown in Figure A.2. The mass flow rate of the air to the space (flow rate [kg/s]), varies to maintain the air temperature in the space at a given set point to maintain comfort in the space. The temperature of the air at the return to the space-heating system (Return Temperature [°C]), varies based on heating load in the space and may be approximately 21°C.
Figure A.2. Typical Air-Based Space-Heating System
A.2 Service-Water Heating System
In the models, a natural-gas fueled boiler is used to heat service water (heated water used in restrooms and in kitchens) in both small and large office building models. According to the DOE reference models, the usage in an office building is assumed to be 1 gallon per occupant per day divided evenly over a 9 hour period (the length of a typical work day). Similar assumptions are established for other building types simulated in this work. The supply water temperature from the boiler in the model is maintained at 60°C (in actual buildings the temperature of the water from the faucet is typically not higher than 50°C to prevent scalding or burns). The temperature of the makeup water is determined by the city supply water temperature and is assumed to be between 14.3 and 18.5°C, and is a function of the season.
The value of the net demand required to meet the service-water heating set point (service-water heating demand [kW]) is calculated independently of the efficiency of the heating equipment and is 551 kWh for the small office building in San Francisco. The average service-water heating demand (when the system is operating) on a typical winter weekday is 1.7 kW for the small office building.
The value of the fluid mass flow rate at the inlet to the service-water heating system (service-water heating system flow rate [kg/s]) varies based on service-water use in the space.
A.3 Calculation of Heating Load Potentially Accessible by Fuel Cell
System
The time series data from the simulation includes the heating system supply and return temperatures [ , ] and flow rate [ ]. These values are based on satisfying the building demand 100% of the time. Flow of heat [ ] to the building space or the building, hot water is calculated using the equation:
where is the specific heat of water at 4.181 kJ/kg°C [1.006 kJ/kg°C for dry air]
We calculate the portion of building heating demand at low enough temperature that this heat could be served by an HTPEM FCS [ ] assuming the return water (air in the case of an air-based system) is heated to the FCS exhaust temperature at the outlet of the heat exchanger [ ]; in this preliminary study, heat exchanger characteristics and limitations are not considered. The term is therefore calculated based on the equation:
max ,
0 (A.2) The above calculation is performed at each time step and is repeated for space heating as well as
service-water heating. The resulting total heating demand that could potentially be served by an FCS is the sum of the space-heating demand accessible by the FCS and the service-water heating demand accessible by the FCS.