The Thermostatically Controlled Loads (TCL) steps are used to define the parameters for a virtual battery that modulates cooling or heating operation for demand response. Each TCL specifies a unique virtual battery that is operated in conjunction with other TCL type batteries. The TCL is modeled using an equivalent thermal parameter (ETP) model, which describes the system in terms of a simple DC circuit. In this formulation, temperature is described as circuit voltage, the thermal conductance of a system’s envelope as charge conductance (UA), the thermal mass of a system as capacitance (C), and heat flow as current flow. For air conditioning and heating, the system is the home itself, whereas for refrigeration or hot water heating, the system is an individual piece of equipment. For more information on the ETP model, see GridLAB-D documentation and for how the model is used to describe a virtual battery, see the main VB documentation page.
Housing Unit Type
The selection of Housing Unit Type determines several parameters that are used to calculate the Generalized Battery Model (GBM):
- Default number of units for the selected region (see this page for more info on location selection)
- House geometry characteristics
- Conditioned area
- House (or equipment) envelope thermal characteristics
The table below shows house thermal characteristics as a function of housing unit type and year built.
| Year Range | House Type | Rroof | Rwall | Rfloor | Rdoor | Uwindow | Volumetric air exchange rate, I | Coefficient of Performance (COP) |
|---|---|---|---|---|---|---|---|---|
| < 1939 | single | 16 | 10 | 10 | 3 | 1.27 | 0.75 | 2.6 |
| 1940-1949 | single | 19 | 11 | 12 | 3 | 0.81 | 0.75 | 2.75 |
| 1950-1959 | single | 19 | 14 | 16 | 3 | 0.81 | 0.5 | 2.9 |
| 1960-1969 | single | 30 | 17 | 19 | 3 | 0.6 | 0.5 | 3.1 |
| 1970-1979 | single | 34 | 19 | 20 | 3 | 0.6 | 0.5 | 3.3 |
| 1980-1989 | single | 36 | 22 | 22 | 5 | 0.47 | 0.25 | 3.4 |
| 1990-2005 | single | 48 | 28 | 30 | 11 | 0.31 | 0.25 | 3.5 |
| > 2006 | single | 48 | 28 | 30 | 11 | 0.31 | 0.25 | 3.5 |
| < 1959 | apartment | 13 | 12 | 9 | 2 | 1.27 | 0.75 | 2.35 |
| 1960-1989 | apartment | 20 | 12 | 13 | 3 | 0.6 | 0.25 | 2.5 |
| 1990-2005 | apartment | 29 | 14 | 13 | 6 | 0.33 | 0.13 | 2.65 |
| > 2006 | apartment | 29 | 14 | 13 | 6 | 0.33 | 0.13 | 2.65 |
| < 1959 | mobile | 13 | 9 | 12 | 2 | 1.27 | 0.75 | 2.35 |
| 1960-1989 | mobile | 13 | 9 | 12 | 2 | 1.27 | 0.75 | 2.35 |
| 1990-2005 | mobile | 24 | 12 | 18 | 3 | 0.47 | 0.75 | 2.85 |
| > 2006 | mobile | 24 | 12 | 18 | 3 | 0.47 | 0.75 | 2.85 |
Source: PNNL demand response report found here combined with GridLAB-D documentation found here (for U-values).
TCL Parameters
For air conditioners and heat pumps, the conditioned area is used along with aggregated data from NEEA’s Residential Building Stock Assessment (RBSA) database to calculate each TCL’s rated power and coefficient of performance (COP). For refrigerators and hot water heaters, these values are taken from this ACEEE conference paper and Hao (2015), respectively (see table below).
| TCL Type | Rated Power | COP |
|---|---|---|
| Air conditioner | 4.85 W/ft2 | 3.32 |
| Heat pump | 5.2 W/ft2 | 2.4 |
| Refrigerator | 249 W | 1.64 |
| Water heater | 4500 W | 1 |
The house thermal characteristics are used to calculate a home’s thermal conductance (\(U_A\)) and thermal mass (\(C\)) for air conditioning and heating as follows:
\( A_{exterior} = 2 \times n_{floors} \times h \times (1+rat_{floor})+\sqrt{\frac{A}{n_{floors} \times rat_{floor}}} \times EWR\)
\( A_{window} = A_{exterior} \times WWR\)
\( A_{door} = A_{sgldoor} \times n_{door}\)
\( A_{wall} = A_{exterior} – A_{window} – A_door\)
\( A_{ceiling} = \frac{A \times ECR}{n_{floors}} \)
\( A_{floor} = \frac{A \times EFR}{n_{floor}}
[latex] U_A = A_{window} U_{window} + A_{door} / R_{door} + A_{wall} / R_{wall} \\ \quad + A_{roof} / R_{roof} + 0.018 \times h \times I \ [Btu/(^{\circ} F \cdot hr)]\)
\( R = 1/U_A \ [(^{\circ} F \cdot hr)/Btu] \)
\( C = A m_f \,-\, 2 \times 0.018 A h \ [Btu/^{\circ} F]\)
where:
\( A_{x} = \) area of x, \([ft^{2}]\)
\( U_{x} = \) u-value of x, \([Btu/(^{\circ} F \cdot ft^{2} \cdot hr)]\)
\( R_{x} = \) r-value of x, \([(^{\circ} F \cdot ft^{2} \cdot hr)/Btu]\)
\( n_{x} = \) number of x
\( rat_{floor} = \) aspect ratio of the housing structure (width of the structure divided by the length)
\( EWR = \) fractional percentage of the structure’s envelop walls that are exposed to the outside environment
\( WWR = \) fractional percentage of window area relative to the total exterior surface area
\( ECR = \) fractional percentage of the ceiling that abutts the outside environment
\( EFR = \) fractional percentage of the floor that abutts the outside environment
\( R = \) equivalent resistance of home, \([(^{\circ} F \cdot ft^{2} \cdot hr)/Btu]\)
\( 0.018 = \) volumetric heat capacity of air at standard conditions, \([Btu/(^{\circ} F \cdot ft^{3})]\)
\( A = \) home square footage, \([ft^{2}]\)
\( h = \) home ceiling height, \([ft]\)
\( I = \) volumetric air exchange rate, \([1/hr]\)
\( m_f = \) Total thermal mass per unit floor area, \([Btu/(^{\circ} F \cdot ft^{2})]\)
The default values for the above parameters that are used in calculating the home’s thermal conductance and mass are given by housing structure type in the following table:
| Parameter | Detached Single-Family Homes | Attached Single-Family Homes | Apts. in Buildings with 2-4 Units | Apts. in Buildings with 5+ Units | Mobile Homes |
|---|---|---|---|---|---|
| Floor aspect ratio | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 |
| Ceiling height | 8 ft. | 8 ft. | 8 ft. | 8 ft. | 8 ft. |
| Exterior ceiling fractional percent | 1 | 1 | 0 | 0 | 1 |
| Exterior floor fractional percent | 1 | 1 | 0 | 0 | 1 |
| Exterior wall fractional percent | 1 | 0.5 | 0.5 | 0.25 | 1 |
| Window fractional percent | 0.07 | 0.07 | 0.07 | 0.07 | 0.07 |
| Number of doors | 2 | 2 | 1 | 0 | 1 |
| Area of a single door | 19.5 ft2 | 19.5 ft2 | 19.5 ft2 | 19.5 ft2 | 19.5 ft2 |
| Number of floors | 2 | 2 | 1 | 1 | 1 |
| Air exchange rate | 0.5 1/hr | 0.5 1/hr | 0.5 1/hr | 0.5 1/hr | 0.5 1/hr |
Note: After thermal conductance (\(U_A\)) and thermal mass (\(C\)) have been computed, they are converted to SI units: \([kWh/(^{\circ} C \cdot hr) ]\) and \([kWh/^{\circ} C]\), respectively.
| TCL Type | R (oC/kW) | C (kWh/oC) |
|---|---|---|
| Refrigerator | 90 | 0.6 |
| Water heater | 120 | 0.4 |
Temperature Set Point and Deadband
The temperature set point and deadband are used to specify the target TCL temperature and allowable range under virtual battery operation, as shown in the figure below. These are used to calculate GBM parameters.
Number of Units
The number of housing units is pre-populated based on the housing type and selected Virtual Battery location, as described above. This value is used in the calculation of the GBM parameters (see this page for more info).