House

In this section, we describe the residential and small commercial building thermal load calculation, the modeling approach, major assumption and model testing and validation.

The major heat gains and losses that contribute to the building cooling or heating load consist of the following:

1. Conduction through exterior walls, roof, and glass
2. Heat gain/loss from infiltration of outside air through opening
3. Solar radiation through glass
4. Internal gains from lighting, people, equipment

Items 1, 2, and 3 are considered driven by the external source, while item 4 is consider internally generated. The thermal load can be either sensible or latent. Sensible load results in increase/decrease in the air temperature; latent load results in increase/decrease of water vapor, which increases/decreases the humidity. Items 1 and 3 are solely sensible, items 2 can be both sensible and latent, internal gains from lights are sensible and internal gains from people and equipment can be both sensible and latent.

In general, the amount of heat that must be removed (cooling load) or added (heating load) is not always equal to the amount of heat received or lost at a given time. The difference is a result of the heat storage and time lag effects [citation]. Only a portion of the heat entering or leaving building actually heats/cools the room air immediately; the rest heats the building mass – the roof, walls, floors and building mass and air mass. The heat that is stored in the mass will result in heating/cooling load at a later time. So, the modeling approach will have to account for the storage effect.

To account for the storage effects when estimating the conduction gains from the exterior walls, roofs, and glass cooling load temperature difference method (CLTD) can be used:

Synopsis

class house {
    parent residential_enduse;
    function attach_enduse();
    object weather; 
    double floor_area[sf];
    double gross_wall_area[sf]; 
    double ceiling_height[ft];
    double aspect_ratio;
    double envelope_UA[Btu/degF];
    double window_wall_ratio;
    double number_of_doors; 
    double exterior_wall_fraction;
    double interior_exterior_wall_ratio;
    double exterior_ceiling_fraction;
    double exterior_floor_fraction; 
    double window_shading;
    double window_exterior_transmission_coefficient;
    double solar_heatgain_factor; 
    double airchange_per_hour; 
    double airchange_UA[Btu/degF]; 
        double UA;
    double internal_gain[Btu/h]; 
    double solar_gain[Btu/h]; 
    double incident_solar_radiation[Btu/h]; 
    double heat_cool_gain[Btu/h]; 
        set {NONE=0,H=1,N=2,E=3,S=4,W=5} include_solar_quadrant;
        enumeration {DEFAULT=0,FLAT=1,LINEAR=2,CURVED=3} heating_cop_curve;
    double thermostat_deadband[degF]; 
    int16 thermostat_cycle_time; 
    timestamp thermostat_last_cycle_time; 
    double heating_setpoint[degF]; 
    double cooling_setpoint[degF]; 
    double design_heating_setpoint[degF]; 
    double design_cooling_setpoint[degF]; 
    double over_sizing_factor; 
    double design_heating_capacity[Btu/h]; 
    double design_cooling_capacity[Btu/h]; 
    double cooling_design_temperature[degF]; 
    double heating_design_temperature[degF]; 
    double design_peak_solar[Btu/h]; 
    double design_internal_gains[Btu/h]; 
    double air_heat_fraction[pu]; 
    double mass_solar_gain_fraction[pu]; 
    double mass_internal_gain_fraction[pu]; 
    double auxiliary_heat_capacity[Btu/h]; 
    double aux_heat_deadband[degF]; 
    double aux_heat_temperature_lockout[degF]; 
    double aux_heat_time_delay[s]; 
    double cooling_supply_air_temp[degF]; 
    double heating_supply_air_temp[degF]; 
    double duct_pressure_drop[inh2o]; 
    double fan_design_power[W]; 
    double fan_low_power_fraction[pu]; 
    double fan_power[kW]; 
    double fan_design_airflow[cfm]; 
    double fan_impedance_fraction[pu]; 
    double fan_power_fraction[pu]; 
    double fan_current_fraction[pu]; 
    double fan_power_factor[pu]; 
    double heating_demand; 
    double cooling_demand; 
    double heating_COP[pu]; 
    double cooling_COP[Btu/kWh]; 
    double air_temperature[degF]; 
    double outdoor_temperature[degF]; 
    double outdoor_rh[%]; 
    double mass_heat_capacity[Btu/degF]; 
    double mass_heat_coeff[Btu/degF]; 
    double mass_temperature[degF]; 
    double air_volume[cf]; 
    double air_mass[lb]; 
    double air_heat_capacity[Btu/degF]; 
    double latent_load_fraction[pu]; 
    double total_thermal_mass_per_floor_area[Btu/degF];
    double interior_surface_heat_transfer_coeff[Btu/h];
    double number_of_stories; 
    double is_AUX_on; 
    double is_HEAT_on; 
    double is_COOL_on; 
    double thermal_storage_present; 
    double thermal_storage_in_use; 
    set {RESISTIVE=16, TWOSTAGE=8, FORCEDAIR=4, AIRCONDITIONING=2, GAS=1} system_type; 
    set {LOCKOUT=4, TIMER=2, DEADBAND=1, NONE=0} auxiliary_strategy; 
    enumeration {AUX=3, COOL=4, OFF=1, HEAT=2, UNKNOWN=0} system_mode; 
    enumeration {AUX=3, COOL=4, OFF=1, HEAT=2, UNKNOWN=0} last_system_mode; 
    enumeration {RESISTANCE=4, HEAT_PUMP=3, GAS=2, NONE=1} heating_system_type;
    enumeration {HEAT_PUMP=2, ELECTRIC=2, NONE=1} cooling_system_type;
    enumeration {ELECTRIC=2, NONE=1} auxiliary_system_type;
    enumeration {TWO_SPEED=3, ONE_SPEED=2, NONE=1} fan_type;
    enumeration {UNKNOWN=7, VERY_GOOD=6, GOOD=5, ABOVE_NORMAL=4, NORMAL=3, BELOW_NORMAL=2, LITTLE=1, VERY_LITTLE=0} thermal_integrity_level; 
    enumeration {LOW_E_GLASS=2, GLASS=1, OTHER=0} glass_type; 
    enumeration {INSULATED=4, WOOD=3, THERMAL_BREAK=2, ALUMINIUM=1, ALUMINUM=1, NONE=0} window_frame; 
    enumeration {HIGH_S=5, LOW_S=4, REFL=3, ABS=2, CLEAR=1, OTHER=0} glazing_treatment; 
    enumeration {OTHER=4, THREE=3, TWO=2, ONE=1} glazing_layers; 
    enumeration {FULL=2, BASIC=1, NONE=0} motor_model; 
    enumeration {VERY_GOOD=4, |GOOD=3, AVERAGE=2, POOR=1, VERY_POOR=0} motor_efficiency; 
    int64 last_mode_timer;
    double hvac_motor_efficiency[unit]; 
    double hvac_motor_loss_power_factor[unit]; 
    double Rroof[Btu/degF.h]; 
    double Rwall[Btu/degF.h]; 
    double Rfloor[Btu/degF.h]; 
    double Rwindows[Btu/degF.h]; 
    double Rdoors[Btu/degF.h]; 
    double hvac_breaker_rating[A]; 
    double hvac_power_factor[unit]; 
    double hvac_load[kW]; 
    double last_heating_load; 
    double last_cooling_load; 
    complex hvac_power; 
    double total_load; 
    end use panel; 
    double design_internal_gain_density[W/sf]; 
    bool compressor_on;
    int64 compressor_count;
    timestamp hvac_last_on;
    timestamp hvac_last_off;
    double hvac_period_length;
    double hvac_duty_cycle;
    enumeration {NONE=2, BAND=1, FULL=0} thermostat_control; 
}

Example

Basic House

The default house does not require any parameters be set. Thus, the minimum allowed specification for a single family house is:

module residential;
object house {
}

With no parameters specified, the default parameters are inhereted, specified in the table below.

Table 1: Default House Parameter Values

Parameter	Default value
load.power_fraction	0.8
load.impedance_fraction	0.2
load.current_fraction	0.0
design_internal_gain_density	0.6 [W/sf]
thermal_integrity_level	UNKNOWN
hvac_breaker_rating	0.0 [A]
hvac_power_factor	0.0
Tmaterials	0.0 [degF]
cooling_supply_air_temp	50.0 [degF]
heating_supply_air_temp	150.0 [degF]
heating_system_type	HEAT_PUMP
cooling_system_type	UNKNOWN
auxiliary_system_type	UNKNOWN
fan_type	UNKNOWN
fan_power_factor	0.96
fan_current_fraction	0.7332
fan_impedance_fraction	0.2534
fan_power_fraction	0.0135
glazing_layers	TWO
glass_type	LOW_E_GLASS
glazing_treatment	CLEAR
window_frame	THERMAL_BREAK
motor_model	NONE
motor_efficiency	AVERAGE
hvac_motor_efficiency	1.0
hvac_motor_loss_power_factor	0.125
hvac_motor_real_loss	0.0
hvac_motor_reactive_loss	0.0
is_AUX_on	FALSE
is_HEAT_on	FALSE
is_COOL_on	FALSE
thermal_storage_present	FALSE
thermal_storage_inuse	FALSE

Implicit end uses

To enable implicit end uses in the house model, add or remove the desired end uses (all caps) that you wish to include.

module residential {
   implicit_enduses LIGHTS|PLUGS|OCCUPANCY|NONE;
}

Properties

The following tables describe the available properties for definition in a house object. These properties are organized into the following categories: physical design, HVAC design, heatflow, fan design, thermostat, derived, load, and enumerations.

Table 2: Physical Design Properties

Property name	Type	Unit	Description	Default Value
floor_area	double	sf	Home conditioned floor area	2,500 ft²
gross_wall_area	double	sf	Gross outdoor wall area
ceiling_height	double	ft	Average ceiling height	8 ft
aspect_ratio	double	none	Aspect ratio of the home's footprint
window_wall_ratio	double	none	Ratio (WWR) of window area to wall area	0.15
number_of_doors	double	none	Number of doors	4
exterior_wall_fraction	double	none	Ratio (EWR)of exterior wall ratio to wall area	100%
interior_exterior_wall_ratio	double	none	Ratio of interior to exterior walls	1.5
exterior_ceiling_fraction	double	none	Ratio (ECR) of external ceiling sf to floor area	100%
exterior_floor_fraction	double	none	Ratio (EFR) of floor area used in UA calculation	100%
number_of_stories	double	none	Number of stories within the structure	1
Rroof	double	degF.sf.h/Btu	Roof R-value	30 °F.ft².hr/Btu
Rwall	double	degF.sf.h/Btu	Wall R-value	19 °F.ft².hr/Btu
Rfloor	double	degF.sf.h/Btu	Floor R-value	22 °F.ft².hr/Btu
Rwindows	double	degF.sf.h/Btu	Window R-value
Rdoors	double	degF.sf.h/Btu	Door R-value	5 °F.ft².hr/Btu
window_shading	double	none	Transmission coefficient through window due to glazing
window_exterior_transmission_coefficient	double	none	(WETC) Coefficient for the amount of energy that passes through window	60%
area_per_door	double	sf	Area per exterior door	19.5 ft²

The primary values for the thermal envelope of a modeled house are Rroof, Rwall, Rfloor, Rwindows, and Rdoors. The R-value of a surface is the inverse of its U-value. If one or more of these values are set explicitly, they will be used over the values set by the following options for that field.

Two methods exist for describing the HVAC system presence. The first method exclusively uses the system_type property for describing a house's HVAC system, described later in the enumerations table, such as GAS, AIRCONDITIONING, or RESISTIVE. This high level description contains a set of values joined by pipes to describe the system. If neither GAS nor RESISTIVE are set, the model will assume that a given house has a heat pump, a one-speed central ventilation fan, auxiliary heating with an auxiliary deadband for heating.

The second method uses a combination of heating_system_type, cooling_system_type, auxiliary_system_type, auxiliary_strategy, and fan_type to describe the HVAC system more explicitly. The three system types controls what mechanism, if any, is used. The fan_type controls the presence of central ventilation and whether or not it has a low-power setting. Auxiliary heat strategies can be put together with pipes (with the exception of "NONE", which has adds nothing) to combine the control options.

It is assumed that any system with a heat pump will have electric auxiliary heating, and that any system with central heating or cooling will include a fan for circulation.

Table 3: HVAC Design Properties

Property name	Type	Unit	Description	Default Value
cooling_design_temperature	double	degF	System cooling design temperature	75°F
heating_design_temperature	double	degF	System heating design temperature	70°F
design_peak_solar	double	Btu/h	System design solar load
design_internal_gains	double	Btu/h	System design internal gains	A function of floor area (see Design Internal Gains)
cooling_supply_air_temp	double	degF	Temperature of air blown out of the cooling system	50°F
heating_supply_air_temp	double	degF	Temperature of air blown out of the heating system	150°F
duct_pressure_drop	double	in	End-to-end pressure drop for the ventilation ducts (inches of water)	\(\frac{1}{2}\)
heating_COP	double	pu	System heating performance coefficient	3.50
cooling_COP	double	Btu/kWh	System cooling performance coefficient	3.50
design_heating_capacity	double	Btu/h	System heating capacity
design_cooling_capacity	double	Btu/h	System cooling capacity
design_heating_setpoint	double	degF	System design heating setpoint
design_cooling_setpoint	double	degF	System design cooling setpoint
auxiliary_heat_capacity	double	Btu/h	Installed auxiliary heating capacity
over_sizing_factor	double	unit	Over sizes the heating and cooling system from standard specifications (0.2 = 120% sizing)	0%

Example HVAC Configurations

The following snippets can be used to define the HVAC system within a house. The two methods will results in the same system in both cases. The values for the houses with the separate system types are being set explicitly for clarity, even if the defaults would apply the same value.

Only one method is listed for the auxiliary heating strategies because the older style of describing the HVAC system did not include options for auxiliary heating types, presence, or strategies. A combination with system_type, auxiliary_system_type, and auxiliary_strategy, will work without options colliding.

Gas heating

object house{
 system_type GAS;
}

object house{
 heating_system_type GAS;
 cooling_system_type NONE;
 auxiliary_system_type NONE;
}

Heat pump

object house{
 system_type AIRCONDITIONING|FORCEDAIR;
}

object house{
 heating_system_type HEAT_PUMP;
 cooling_system_type HEAT_PUMP;
 auxiliary_system_type ELECTRIC;
 auxiliary_system_type DEADBAND;
 fan_type ONE_SPEED;
}

Heat pump with two-speed fan

object house {
 system_type AIRCONDITIONING|TWOSTAGE;
}

object house{
 heating_system_type HEAT_PUMP;
 cooling_system_type ELECTRIC;
 fan_type TWO_SPEED;
 auxiliary_system_type ELECTRIC;
 auxiliary_strategy DEADBAND;
}

Baseboard heating

object house{
 system_type RESISTIVE;
}

object house{
 heating_system_type RESISTANCE;
 cooling_system_type NONE;
 auxiliary_system_type NONE;
 fan_type NONE;
}

Electric heat and central air

object house{
 system_type RESISTIVE|FORCEDAIR;
}

object house{
 heating_system_type RESISTANCE;
 cooling_system_type NONE;
 auxiliary_system_type NONE;
 fan_type ONE_SPEED;
}

Auxiliary heat with timer

object house{
 heating_system_type HEAT_PUMP;
 cooling_system_type ELECTRIC;
 auxiliary_system_type ELECTRIC;
 auxiliary_strategy TIMER;
}

Auxiliary heat with deadband

object house{
 heating_system_type HEAT_PUMP;
 cooling_system_type ELECTRIC;
 auxiliary_system_type ELECTRIC;
 auxiliary_strategy DEADBAND;
}

Auxiliary heating with Timer and Lockout

object house{
 heating_system_type HEAT_PUMP;
 cooling_system_type ELECTRIC;
 auxiliary_system_type ELECTRIC;
 auxiliary_strategy TIMER|LOCKOUT;
}

Auxiliary heating with Deadband and Lockout

object house{
 heating_system_type HEAT_PUMP;
 cooling_system_type ELECTRIC;
 auxiliary_system_type ELECTRIC;
 auxiliary_strategy DEADBAND|LOCKOUT;
}

Auxiliary heating with Deadband, Lockout, and Timer

object house{
 heating_system_type HEAT_PUMP;
 cooling_system_type ELECTRIC;
 auxiliary_system_type ELECTRIC;
 auxiliary_strategy DEADBAND|LOCKOUT|TIMER;
}

Auxiliary Strategy

Options for the control strategy for auxiliary heating in the house are:

Strategy	Description
NONE	If auxiliary heat is being used, at least one auxiliary_strategy should be specified.
LOCKOUT	Auxiliary heat will come "on" whenever thermostat calls for heating and outdoor air temperature is below the value set for aux_heat_temperature_lockout. It remains "on" until the thermostat is satisfied.
DEADBAND	(default) Auxiliary heat will come "on" when indoor air temperature drops by more than the value set for aux_heat_deadband below the heating_setpoint. It remains "on" until the thermostat is satisfied.
TIMER	Auxiliary heat will come "on" when heating_system_type has been "on" for longer than the value specified for aux_heat_time_delay. It remains "on" until the thermostat is satisfied.
Default	When auxiliary_system_type is set to ELECTRIC, the default setting for auxiliary_strategy is DEADBAND (with 2 degF).

Design Internal Gains

The design internal gains as a function of floor area are approximated as a regression against mean annual ELCAP consumption data for the “Other” end use by floor area categories, as follows (from spreadsheets ELCAP Load Shapes_Q3.xls and Internal Gains Default.xls):

Table 4: Regression of ELCAP “Other” Annual End Use Load vs. Floor Area

End Use	Size of Home (ft 2)	Regression: ln(Other) = ln(a) + b ln(x)*
850	1350	2100
Other	6730	7298
ln( End Use )	ln( Size of Home (ft 2) )	b
6.745	7.208	7.650
ln( Other )	8.814	8.895
Predicted End Use	Size of Home (ft 2)	EU = a xb
850	1350	2100
Other	6403	7856

For the “Other” end use (excludes heating and water heating) in the ELCAP metered end use data project, the results of a linear regression of the average annual energy consumption as a function of floor area of the form Other = a xb can be converted by an axis transformation into a linear regression of the form

with the resulting coefficients a and b shown in the table above.

Also from ELCAP, the ratio of the maximum hourly load of the summer average load shape to the mean hourly load for the year is 1.32 (hour 18). Combined with the regression results, and converting the units from kWh/yr to Btu/hr, the design internal gains as a function of floor area is

Design_internal_gains = 324.9 * (floor_area)0.442 * 1.32 * 3413 / 8760

Air Conditioning (Cooling)

House_e only supports electrically-powered forced-air vapor-compression cooling, which can represent either a central air conditioner or a window/wall unit that cycles on and off to maintain the air temperature below the cooling thermostat setpoint. This is defined as an electric Cool_system_type. If no air conditioning is provided, input none for this parameter.

An air conditioner uses an electrically-powered refrigerant pump to move heat from the cooled space and reject it outdoors. Hence, it can remove more heat from the house than the electricity input to the pump, and the COP is thus typically much greater than 1.0 (conservation of energy requires that the heat rejected outdoors is equal to the heat removed from the house plus the energy input to the pump).

The laws of thermodynamics governing the vapor-compression cycle show that the COP decreases as the outdoor temperature increases, because of the increased difficulty of rejecting the heat outdoors. House_e models this phenomena. Similarly, the COP decreases as the supply air temperature decreases, and as the temperature and humidity of the air from the house increase, but these variations are assumed to be relatively small and House_e does not model them.

Default values for the other input parameters are characteristic of a central air conditioner or heat pump. Window/wall air conditioners generally are less efficient, so the Cooling COP under standard conditions is likely to be lower than the default value. A house may utilize multiple window/wall air conditioners in different locations, each with its own thermostat. House_e simulates them together as a single equivalent unit controlled by a single thermostat. It is not uncommon for these units to be too small to keep a house at the cooling setpoint during very hot weather. If this is the case, the user can specify a negative oversizing factor.

Heating

House_e supports a variety of heating system types:

• The absence of a heating system is indicated by a heat_system_type parameter of value none.
• In a resistance heat_system_type, heat is provided by an electric resistance heating coil (either in a forced-air furnace, or electric baseboard radiators) that cycles on and off to try to maintain the air temperature above the heating thermostat setpoint. The COP of a resistance heating system is a constant 1.0, being unaffected by the outdoor air temperature. The capacity is likewise unaffected.
• In a gas heat_system_type, heat is provided by a gas-powered furnace or a boiler that cycles on and off to try to maintain the air temperature above the heating thermostat setpoint, but places no load on the electricity distribution system (except for its fan; see the next section). Its capacity is a constant unaffected by the outdoor air temperature. This can be used to model heating systems supplied by natural gas, propane, wood/biomass, and other non-electric sources.
• In a heat pump heat_system_type, heat is provided by a heat pump that is a reversible vapor compression cycle, i.e. and air conditioner running in "reverse" that pumps heat from outdoors and rejects it indoors. It cycles on and off to try to maintain the air temperature above the heating thermostat setpoint, but places no load on the electricity distribution system( excpet for its fan; see the next section). Its capacity is a constant unaffected by the outdoor air temperature.

Like an air conditioner, a heat pump's heating COP is not a constant, but instead decreases as the outdoor temperature decreases, because of the increased difficulty of pumping heat from outdoors. House_e models this phenomena. Similarly, the COP and capacity decrease as the supply air temperature increases and as the temperature of the air from the house increases, but these variations are assumed to be relatively small and House_e does not model them.

Auxiliary heating (For Heat Pumps Only)

An auxiliary heating system can be specified for a heat pump heat_system_type by providing a value of electric for the input parameter auxiliary_heat. A heat pump is generally sized to meet the peak cooling requirement, and its heating capacity under standard conditions is generally equal to its cooling capacity. Given its reduced output at very cold outdoor temperatures, it may not have enough capacity to maintain the house at the desired heating setpoint. An auxiliary heat system serves this function. A value of none for the Auxilairy_heat parameter indicates no such auxiliary heat is provided.

If auxiliary heat is specified (the default), then a control strategy for it must also be specified. Three types of control can be modeled by House_e. Atleast one must be specified; two or all three can be specified to work in combination. Each auxiliary heat control strategy can call for auxiliary heat to turn on and the heat pump heating cycle to turn off. The auxiliary heat control strategies supported by House_e are:

• If a value is provided for the auxiliary_heat_deadband input parameter, then the auxiliary heat comes "on" when the indoor air temperature drops by more than the value below the heating setpoint and remains "on" until the thermostat is satisfied (i.e., when the heating system would normally go "off"). This is the default control strategy (value = 2°F) and the most common one in usage in the U.S in the decades 1980-2010. The problem with it is that if the thermostat is set back at night , it will trigger auxiliary heat when the thermostat is set up in the morning, even under relatively warm conditions.

• If a value is provided for the auxiliary_heat_lockout_temperature input parameter, then the auxiliary heat comes "on" whenever the thermostat calls for heating and the outdoor air temperature is below value. It remains "on" until the thermostat is satisfied (i.e.,when the heating system would normally go "off"). The default value = none. This is an older control strategy particularly common to early heat pump systems in the U.S.

• If a value is provided for the Auxiliary_time_delay input parameter, then the auxiliary heat comes "on" whenever the heating system has been "on" for more than value minutes but the heating thermostat remains unsatisfied. The auxilairy heat remains "on" until the thermostat is satisfied (i.e.,when the heating system would normally go "off"). The default value is none. This is the most advanced control strategy and is designed to minimize auxiliary heating by giving the heat pump a chance to satisfy the heating requirement before turning to auxiliary heat.

Circulation Fan

Air conditioners and heat pumps require a fan to be specified (Fan_type parameter equal to /-speed or 2-speed). For resistance heating systems without an air conditioning, a fan is optional. If fan_type is none , then the heating system is implicitly a baseboard/radiator system. A fan is assumed to be present, and will be sized to meet the larger of the heating or cooling air flow rate required to meet the heating and cooling design loads, respectively.

A 1-speed Fan_type is "on" when the cooling, heating, or auxiliary heating system is "on". This is the default, and the most common case in the u.S.

The heat from the power to the fan is added to the output of the HVAC system, and the power is add to the electrical load placed by the HVAC system on the electric distribution system.

A 2-speed Fan_type is "on" continually, at full speed when the cooling, heating, or auxiliary heating system is "on", and at low speed to circulate air when the cooling,heating, and auxiliary heating system are each "off" or not present. At low speed, the power of the fan is reduced by the factor of the input parameter Fan_power_low_speed_fraction_of_high_speed. Note that fan power is generally proportional to the square of the flow rate; if the air flow is 50% at low-speed, then the power at low speed is (50%)2 , i.e. 25%.

Table 5: Heatflow Properties

Property name	Type	Unit	Description	Default Value
solar_heatgain_factor	double	none	Product of the window area, window transmitivity, and the window exterior transmission coefficient
airchange_per_hour	double	none	Number of air-changes per hour	0.5 1/hr
internal_gain	double	Btu/h	Internal heat gains	50%
solar_gain	double	Btu/h	Solar heat gains	50%
incident_solar_radiation	double	Btu/h.sf	Average incident solar radiation hitting the house
heat_cool_gain	double	Btu/h	System heat gains(/losses)
air_heat_fraction	double	pu	Fraction of the heat gain/loss that goes to air (as opposed to mass)
mass_heat_capacity	double	Btu/degF	Interior mass heat capacity
mass_heat_coeff	double	Btu/degF.h	Interior mass heat exchange coefficient
air_heat_capacity	double	Btu/degF	Air thermal mass
total_thermal_mass_per_floor_area	double	Btu/degF.sf	Total thermal mass per floor area	2.0 Btu/°F.ft²
interior_surface_heat_transfer_coeff	double	Btu/h.degF.sf	Interior surface heat transfer coefficient	1.46 Btu/hr.°F.ft²
design_internal_gain_density	double	W/sf	Average density of heat generating devices in the house

Table 6: Fan Design Properties

Property name	Type	Unit	Description
fan_design_power	double	W	Designed maximum pwer draw of the ventilation fan
fan_low_power_fraction	double	pu	Fraction of ventilation fan power draw during low-power mode (two-speed only)
fan_power	double	kW	Current ventilation fan power draw
fan_design_airflow	double	cfm	Designed airflow for the ventilation system
fan_impedance_fraction	double	pu	Impedance component of fan ZIP load
fan_power_fraction	double	pu	Power component of fan ZIP load
fan_current_fraction	double	pu	Current component of fan ZIP load
fan_power_factor	double	pu	Power factor of the fan load
hvac_motor_efficiency	double	unit	Percent efficiency of HVAC motor when using motor model
hvac_motor_loss_power_factor	double	unit	Power factor of motor loasses when using motor model

Table 7: Thermostat Properties

Property name	Type	Unit	Description	Default Value
heating_setpoint	double	degF	Thermostat heating setpoint	70°F
cooling_setpoint	double	degF	Thermostat cooling setpoint	75°F
aux_heat_deadband	double	degF	Temperature offset from standard heat activation to auxiliary heat activation	2.0°F
aux_heat_temperature_lockout	double	degF	Temperature at which auxiliary heat will not engage above	none
aux_heat_time_delay	double	s	Time required for heater to run until auxiliary heating engages	none
thermostat_deadband	double	degF	Deadband of thermostat control	2.0°F
thermostat_cycle_time	int16	none	Mimimum time in seconds between thermostat updates	120s
thermostat_last_cycle_time	timestamp	none	Last time the thermostat changed state
last_mode_timer	int64	none

Table 7. Derived Properties

Table 8: Derived Properties

Property name	Type	Unit	Description	Default Value
air_temperature	double	degF	Indoor air temperature. If not explicitly defined, will set to a random value between 60F and 140F
outdoor_temperature	double	degF	Outdoor air temperature
mass_temperature	double	degF	Interior mass temperature
air_volume	double	cf	Air volume = ceiling height * floor area	20,000 cf
air_mass	double	lb	Air mass
air_density	double	\(lb/ft^3\)	Density of the air, set automatically	0.735 \(lb/ft^3\)
latent_load_fraction	double	pu	Fractional increase in cooling load due to latent heat	35%
heating_demand	double	none	The current power draw to run the heating system
cooling_demand	double	none	The current power draw to run the cooling system
envelope_UA	double	Btu/degF.h	Overall UA of the home's envelope
airchange_UA	double	Btu/degF.h	Additional UA due to air infiltration

Table 9: Load Properties

Property name	Type	Unit	Description
panel	end use	none	Total panel end use load
hvac_breaker_rating	double	A	Determines the amount of curren the HVAC circuit breaker can handle
hvac_power_factor	double	unit	Power factor of HVAC
hvac_load	double	none	Heating/cooling system load
total_load	double	none	Total load

Table 10: Properties Specified by Enumeration

Property name	Type	Unit	Description	Default Value
system_type	set	none	Describe HVAC system of house. (GAS, AIRCONDITIONING, FORCEDAIR, TWOSTAGE, RESISTIVE)
heating_system_type	enumeration	none	Set heating mechanism for house (RESISTANCE, HEAT_PUMP, GAS, NONE)	HEAT_PUMP
cooling_system_type	enumeration	none	Set cooling mechanism for hosue (HEAT_PUMP, ELECTRIC, NONE)	NONE
auxiliary_system_type	enumeration	none	Can be specified for HEAT_PUMP heating systems (ELECTRIC, NONE)	ELECTRIC
auxiliary_strategy	set	none	Control strategy for auxiliary heat (LOCKOUT, TIMER, DEADBAND, NONE)
system_mode	enumeration	none	Heating/cooling system operation state (UNKNOWN, HEAT, OFF, COOL, AUX)
fan_type	enumeration	none	Circulation fan (TWO_SPEED, ONE_SPEED, NONE)	ONE_SPEED
thermal_integrity_level	enumeration	none	Default envelope UA settings (VERY_GOOD, GOOD, ABOVE_NORMAL, NORMAL, BELOW_NORMAL, LITTLE, VERY_LITTLE, UNKNOWN)
glass_type	enumeration	none	Type of window glass used (LOW_E_GLASS, GLASS, OTHER)	LOW-E Glass
window_frame	enumeration	none	Type of window frame (INSULATED, WOOD, THERMAL_BREAK, ALUMINUM, NONE)	Thermal Break
glazing_treatment	enumeration	none	Treatment that increases the reflectivity of exterior windows (HIGH_S, LOW_S, REFL, ABS, CLEAR, OTHER)	Clear
glazing_layers	enumeration	none	Number of layers of glass in each window (THREE, TWO, ONE, OTHER)	TWO
motor_model	enumeration	none	Indicates the level of detail used in modeling the HVAC motor parameters (FULL, BASIC, NONE)
motor_efficiency	enumeration	none	Describes efficiency of the motor when using a motor model (VERY_GOOD, GOOD, AVERAGE, POOR, VERY_POOR)

Thermal Integrity Table Inputs and Defaults

For the convenience of the user in describing a population of buildings, we allow the thermal properties of the envelope construction to be entered as a table. This is useful because the insulation level of ceilings, walls, floors, and windows tend to be highly correlated, rather than independent, because of construction practices and/or building codes that are a function of the vintage of construction. That is, it is extremely unlikely to find a house with heavily insulated walls, but very little ceiling insulation.

So, the user is allowed to enter the following primary inputs by specifying the thermal integrity level description, rather than each individual parameter, according to the table below.

Table 11: Thermal Integrity Table

Thermal Integrity Level	Description	Roof/Ceilings (°F·ft²·hr/Btu)	Walls (°F·ft²·hr/Btu)	Floors (°F·ft²·hr/Btu)	Layers	Window Glazing	Window Treatment	Window Frame	Doors (°F·ft²·hr/Btu)	Infiltration Air Exchange Rate (1/hr)
VERY_LITTLE (0)	old, uninsulated	11	4	4	1	Glass	Clear	Al	3	1.5
LITTLE (1)	old, insulated	19	11	4	2	Glass	Clear	Al	3	1.5
BELOW_NORMAL (2)	old, weatherized	19	11	11	2	Glass	Clear	Al	3	1.0
NORMAL (3)	old, retrofit upgraded	30	11	19	2	Glass	Clear	Tb	3	1.0
ABOVE_NORMAL (4)	moderately insulated	30	19	11	2	Glass	Clear	Tb	3	1.0
GOOD (5)	very well insulated	30	19	22	2	Low-e glass	Clear	Tb	5	0.5
VERY_GOOD (6)	extremely well insulated	48	22	30	3	Low-e glass	Heat-absorbing	In	11	0.5
UNKNOWN	–	–	–	–	–	–	–	–	–	–

thermal_integrity_level is usable to provide unambiguous insulation settings. It will override any values not already set, but will override that objects initial values. The default value is "UNKNOWN", which will not use the thermal integrity level value lookup table.

Glazing

The type of glass (glass_type), the window frame (window_frame) material, the window glazing (glazing_treatment), and the number of window pane layers (glazing_layers) can all be set, and will be used to fill in the window R-value and the window solar transmission coefficient.

Both "aluminum" and "aluminium" are accepted keyword spellings for the window frame type.

Translate glazing material into glazing material type (gmt) for U-value with a look-up table

IF( OR(GM="glass", GM="low-e glass"), IF(GM="glass", gmt="G", gmt="L"), “Error: unrecognized glazing material" )

Based on Type = GL & gmt, and on WF, look-up the window U-value (\(U_g\)) in Table 1 (produces the default Window U-value = 0.47 Btu/hr-°F-ft2)

Table 12: Window U-Values as a Function of Window Characteristics

Type	Layers	Glazing	U-value (Btu / hr.°F.ft²) by Frame Type
None	Aluminum	Tb	Wood	In
1G	1	Glass	1.04	1.27
2G	2	Glass	0.48	0.81
2L	2	Low-e glass	0.30	0.67
3G	3	Glass	0.31	0.67
3L	3	Low-e glass	0.27	0.64

Ref: Window U-values, AHSRAE Handbook 2005, Table 29.2, Operable

Table 13: Glazing solar heat gain coefficient (glazing_shgc) by window frame type (window_frame)

glazing_treatment	CLEAR	ABS	REFL	LOW_S	HIGH_S
glazing_layers	ONE	TWO	THREE	ONE	TWO
window_frame	NONE	0.86	0.76	0.68	0.73
ALUMINUM	0.75	0.67	0.60	0.64	0.55
THERMAL_BREAK	0.75	0.67	0.60	0.64	0.55
WOOD	0.64	0.57	0.51	0.54	0.46
INSULATED	0.64	0.57	0.51	0.54	0.46

The glazing heat gain coefficient (SHGC) is the fraction of incident solar radiation admitted through a window, or the product of the nominal SHGC and the window exterior transmission coefficient. glazing_shgc is expressed as a value between 0 and 100%, 0 being the least solar heat transmission, and 100% being the most.

\(SHGC = SHGC_{nom}\ WET\ A_g\)

Table 14: Values for Rwindows.

glass_type	LOW_E_GLASS	GLASS	OTHER
glazing_layers	ONE	TWO	THREE
window_frame	NONE	undef	1/0.30
ALUMINUM	undef	1/0.67	1/0.64
THERMAL_BREAK	undef	1/0.47	1/0.43
WOOD	undef	1/0.41	1/0.37
INSULATED	undef	1/0.33	1/0.31

Window Openings

This model is designed to represent the effects of people opening their windows during shoulder temperature periods. This is a complicated human interaction to model, as it is often related to current temperature, forecast of the temperature and other weather conditions, history of temperature, humidity, etc. This model is designed to be a brute force approach to representing this impact.

Basically, you activate the model (simulate_window_openings is FALSE by default), then describe the upper and lower cutoffs of when the window WILL absolutely be open versus absolutely WILL NOT be open (window_low_temperature_cutoff and window_high_temperature_cutoff).

The three coefficients listed below then describe a probability curve between the two cutoff points – the probability of opening or closing a window is now a function of the outside air temperature. The “delta” variable is “how often” to update the model as a function of outdoor air temperature, i.e., if outside air changes by 5 degrees, let's see if the human has changed their mind.

The effect is that if windows are closed, normal operation. If open, the HVAC is overridden (to OFF) and UA is raised by a factor of 10 (which makes heat transfer very fast).

What we don’t have a great model for is the probability curve or what the cutoff values should be! For previous work, we found that a simple linear between the cutoffs was a pretty good representation. I think for cutoffs, we used -2 to +8 around the setpoint.

Table 15: Window Opening Parameters

Parameter	Default Value	Units
simulate_window_openings	FALSE	Boolean
is_window_open	FALSE	double
window_low_temperature_cutoff	60	°F
window_high_temperature_cutoff	80	°F
window_quadratic_coefficient	0	none
window_linear_coefficient	0	none
window_constant_coefficient	1	none
window_temperature_delta	5	°F

Sizing Calculations

This section describes how sensibly sized HVAC units are created.

Design heating load (Btu/hr) = UA * (Design indoor temperature heating – Design outdoor temperature heating)

Design sensible cooling load (Btu/hr) = UA * (Design outdoor temperature cooling - Design indoor temperature cooling) + Design internal gains * 3.413 (Btu/hr-kW) +

Design solar_radiation * Ag * SHGC * WET

Design total cooling load (Btu/hr) = Design_sensible_cooling load * (1 + Latent_cooling_fraction)

For cool system types other than none , the design cooling capacity is nearest 6,000 Btu/hr increment above design cooling load (otherwise the Design_cooling_capacity = 0)

Design_cooling_capacity (Btu/hr) = Round( (Design_total_cooling_load * (1 + Oversizing_ factor) + 3000) / 6000 ) * 6000

Other than for heat pumps, the design heating capacity is nearest 10,000 Btu/hr increment above design heating load (otherwise the Design_heating_capacity (Btu/hr) = 0)

Design_heating_capacity (Btu/hr) = Round( (Design_heating_load * (1 + Oversizing_factor) + 5000) / 10000 ) * 10000 # Heat system types other than heat pump

For heat pumps (only), a rule of thumb is that the heating capacity is equal to the cooling capacity, and the auxiliary heating capacity is equal to the

Design_heating_capacity (Btu/hr) = Design_cooling_capacity # _heat pump_ Heat system type only

For heat pump Heat system types with electric auxiliary heat only:

Auxiliary_capacity (Btu/hr) = Round( (Design_heating_load * (1 + Oversizing_factor) + 5000) / 10000 ) * 10000 # heat pump Heat system type only

For all other cases, the Auxiliary capacity = 0.

For Fan types other than none and Heat system types other than none , determine the volumetric flow rate of air at standard conditions and 150 °F to deliver the greater of the Design_heating_capacity and the Auxiliary_capacity:

Design_heating_airflow = Max(Design_heating_capacity and the Auxiliary_capacity)/( 0.018 * (Design_heating_supply_temperature - Design_indoor_temperature_heating))/ 60

For Cool system types other than none , size a fan to deliver a sufficient volume of air at 50 °F to deliver the Design_cooling _cfm:

Design_cooling_airflow = Design_cooling_capacity /(1 + Latent_fraction)/(0.018 * (Design_indoor_temperature_cooling - Design_cooling_supply_temperature)/60

The power input to the fan is based on the greater of the Design_cooling_airflow and the Design_heating_airflow, assuming a ½ in. of water pressure drop, a 42% efficient fan, and an 88% efficient motor sized to the nearest 1/8 HP (for Fan type none , Fan power = 0)

Fan_power = Round(0.117 * Duct_pressure_drop * Max(Design_cooling_airflow, Design_heating_airflow)/$\frac {0.42}{745.7} + \frac {1}{16})/ \frac{1}{8}))*\frac{1}{8} * \frac{745.7}{0.88}$$

Heating/Cooling Thermostat Operations

For convenience, define a set of HVAC functionality indicators, F, which define the capabilities of the HVAC system and whether they are enabled at a given time:

• Fcool = Boolean(Cool_system_type = electric & cooling system is enabled )

• Fheat = Boolean(Heat_system_type \(\neq\) none & heating system is enabled)

• Faux = Boolean(Heat_system_type = heat pump & Auxiliary_heat = electric & heating system is enabled )

• Ffan = Boolean(Fan type\(\neq\)none)

Also define a set of state variables:

• Coolon = Boolean(Cooling system is “on” )
• Cooloff = Boolean(Cooling system is “off” )=\(1-\text{Cool}_\text{on}\)
• Heaton = Boolean(Cooling system is “on” )
• Heatoff = Boolean( Heating system is “off” )=\(1-\text{Heat}_\text{on}\)

For heat pumps with electric auxiliary heat, define additional functionality indicators and state variables:

• Faux_deadband = Boolean(Faux & \(dT_\text{aux}\neq\)none)
• Faux_lockout=Boolean(Faux & Taux_on\(\neq\)none)
• Faux_delay=Boolean(Faux & taux_on \(\neq\)none )
• Auxon = Boolean( Auxiliary heat is “on” )
• Auxoff = Boolean(Auxiliary heat is “off” ) = 1 - Auxon

Further, define the time (in minutes) from the last state change as thvac.

To initialize the time-series, heating, cooling (and auxiliary heat) are “off”: Coolon = Heaton = Auxon = 0 Cooloff = Heatoff = Auxoff = 1

Cooling Thermostat

• Coolon = Boolean(Cooloff \(t_\text{hvac}\) > \(t_\text{min}\) & \(F_\text{cool}\) & \(T_\text{air}\) > (Tset_cool + ½ dTdeadband))

• Cooloff = Boolean(Coolon&thvac > tmin& Fcool & Tair \(\leq\) (Tset_cool - ½ dTdeadband))

Heating Thermostat

• Heaton = Boolean( Heatoff & thvac > tmin & Fheat & Tair \(\leq\) (Tset_heat - ½ dTdeadband))

• Heatoff = Boolean( Heaton & thvac > tmin & Fheat & Tair > (Tset_heat + ½ dTdeadband) )

Auxiliary Heating Control (Heat Pumps Only)

To allow a state change from heating to auxiliary to occur in a single time step, the heating and cooling state change evaluations should be followed by:

• Auxon = Boolean( Heaton & Auxoff & OR(NOT(Faux_deadband) * ( Tair \(\leq\)( Tset_heat - ½ dTaux) ) & OR (NOT(Faux_lockout * (Tair \(\leq\) Taux) & OR(NOT (Faux_delay,(thvac > taux) )

• Auxoff = Boolean( Auxon & T Faux_deadband * ( Tair > (Tset_heat + dTdeadband) ) & thvac > tmin )

If Auxon then Heatoff = 1 and Heaton = 0

Band control

Under band control regime (e.g., object house {thermostat_control BAND;}), the setpoint and deadband settings are ignore, and instead the HVAC control uses the band control variables:

• TauxOn - The indoor temperature at which auxiliary heating is turned on.

• TheatOn - The indoor temperature at which normal heating is turned on.

• TheatOff - The indoor temperature at which heating is turned off.

• TcoolOff - The indoor temperature at which cooling is turned off.

• TcoolOn - The indoor temperature at which cooling is turned on.

The control regime is used for external controllers that wish to directly control the actual temperatures at which the HVAC system changes state.

No control

Under no control regime, i.e., object house {thermostat_control NONE;}, all control variables are ignored and the HVAC system mode is not changed by any internal logic. The variable system_mode determines the state of the HVAC system and must be controlled directly from the external controller.

Outdoor Temperature Adjustments to Capacity and COP

The DOE-2 building stimulation program provides curves that adjust nameplate COPs and capacities for heat pumps and air conditioners as a function of the wet-bulb temperature (Twb) of the return air and/or the outdoor air temperature (Tout). The curves relevant to the House_e model (from DOE-2 Reference Manual, Part 1, Version 1.2, pg IV.194-199) are shown in Table 5, below. Variables involving CAP refer to capacity and variables involving EIR refer to DOE-2’s energy input ratio, which is the inverse of COP.

Table 16: DOE-2 System-Equipment Default Curves

Keyword	Curve	Variables	Curve Type	Applicable SYSTEM-TYPE(s)	Default Curve Coefficients
COOL-CAP-FT	SDL-C1	Twb,Tout	bi-linear	RESYS	0.59815404
COOL-EIR-FT	SDL-C11	Twb,Tout	bi-linear	RESYS	0.49957503
HEAT-CAP-FT	SDL-C51	Tout	quadratic	RESYS	0.34148808
HEAT-EIR-FT	SDL-C56	Tout	cubic	RESYS	2.03914613

Extracted from Table IV.11, DOE-2 Reference Manual, Part 1, Version 1.2 (pg IV.72-73)

House_e does not explicitly model moisture in the home, so the Twb is assumed to be at the standard test condition 67°F. Eliminating Twb as a variable and inverting the EIR equations to produce equivalent COP equations gives the correction factor equations of the forms:

F_COP_T = \(\frac{1}{EIR-FT} = \frac{1}{(K_{0} + K_{1} * T_{out} + K_{2} * T_{out}^{2} + K_{3} * T_{out}^{3})}\)

F_Capacity_Tout = CAP-FT = \(K_{0} + K_{1} * T_{out} + K_{2} * T_{out}^{2} + K_{3} * T_{out}^{3}\)

The resulting coefficients used by GridLAB-D™ are shown in the Table 6, below.

Table 17: GridLAB-D™ Equipment COP Factors**

HVAC Equipment COP Factor	K 0	K 1	K 2	K 3	Limit
F_Cool_COP_Tout	-0.01363961	0.01066989	0.0	0.0	40
F_Heat_COP_Tout	2.03914613	-0.03906753	0.00045617	-0.00000203	80
F_Cooling_Capacity_Tout	1.48924533	-0.00514995	0.0	0.0	-
F_Heating_Capacity_Tout	0.34148808	0.00894102	0.00010787	0.0	-

These are then used to compute the actual COP and capacity as a function of outdoor temperature, as follows:

Note that part-load effects (the effect of starting a heating/cooling cycle are not yet accounted for in GridLAB-D™). They will be added in a future release.

HVAC and Electrical Loads

1. If the Heat system type is not a heat pump, then the heating capacity is Heating_capacity = Design_heating_capacity

2. If the Heat system type is a heat pump, then the heating capacity is determined using Table 6 and the previous section to evaluate F_Heating_Capacity_Tout

   Heating_capacity = Design_heating_capacity * F_Heating_Capacity_Tout

3. The actual capacity at operating conditions for air conditioning is determined using Table 6 and the previous section to evaluate F_Cooling_Capacity_Tout

   Cooling_capacity = Design_cooling_capacity * F_Cooling_Capacity_Tout

4. The electrical load of the fan is

   Pfan = Ffan * (HVACon * Fan_power +F2-speed* HVACoff * Fan_power_low_speed_fraction

5. The sensible heat provided by the HVAC system to the air (Qhvac), with a sign convention of heating positive and cooling negative, is

   Qhvac = Heaton * Heating_capacity + Auxon * Auxiliary_capacity –Coolon * Cooling_capacity / (1 + Latent_cooling_fraction) + Pfan

6. If use_latent_heat is set to TRUE the latent heat is

   Latent_heat_load = Cooling_capacity * (1 - 1 / Latent_cooling_fraction)

7. if use_latent_heat is set to FALSE, the latent heat is

   Latent_heat_load = 0;

8. If the Heat system type is not a heat pump, then the heating COP is

   Heat_COP = 1

9. If the Heat system type is not a heat pump, then the heating COP is determined using Table 6 and the previous section to evaluate F_Heating_Capacity_Tout

   Heat_COP = Heat_COP_std * F_Heat_COP_Tout

10. The cooling capacity is determined using Table 6 and the previous section to evaluate F_Cool_COP_Tout

    Cool_COP = Cool_COP_std * F_Cool_COP_Tout

11. Define additional HVAC functionality indicators, indicating electricity as the source for heating and the presence of a two-speed fan

    Felectric = Boolean(Heat_system_type = heat pump

    Heat_system_type = resistance )

    F2-speed = Boolean(Fan_type = 2-speed )

12. Define additional state variables indicating that heating/cooling is “on” or “off”

    Hvacon = Boolean( Heaton Coolon )

    Hvacoff = Boolean( Heatoff & Cooloff )

13. The electrical power drawn by the HVAC system (Phvac, kW) is the sum of the heating, cooling, and fan electricity consumption

    Phvac = FelectricHeaton * ( Heating_Capacity / 3.413 (Btu/hr- kW) ) / Heating_COP + (Cooling_Capacity / 3.413 (Btu/hr-kW) ) * 1 + Latent_Cooling_Fraction) / Cooling_COP + Pfan

Related Concepts:

• Residential module
  • User's Guide
  • Appliances
  • house class – Single-family home model.
  • residential_enduse class – Abstract residential end use class.
  • occupantload – Residential occupants (sensible and latent heat).
  • ZIPload – Generic constant impedance/current/power end use load.
• Technical Documents
  • Requirements
  • Specifications
  • Developer notes
  • Technical support document
  • Validation