Residential reference cases: IDEAS and Buildings

Two YAML files describe the same Belgian semi-detached house before and after a deep renovation:

Each file generates the model of either library, with the same geometry, zoning, use and weather:

trano create-model examples/residential_before_renovation.yaml IDEAS
trano create-model examples/residential_before_renovation.yaml Buildings

Both files are written by examples/residential_cases.py, which also prints the sizing below: change the house there, not in the YAML files.

The house

Semi-detached two-storey house in Uccle, 7.4 m x 8.4 m inside, street facade north, garden facade south, gable west and party wall east. Heated floor area 110.6 m2 in six zones.

Zone	Storey	Floor area [m2]	Height [m]	Exposed surfaces	Set point [degC], schedule
Living (with the hall)	ground	40.0	2.6	south, west, north (hall), party wall, slab	21, 7-23 h
Kitchen	ground	15.0	2.6	north, west, slab	21, 7-23 h
Bedroom 1	first	18.5	2.5	south, west, attic floor	18, 6-23 h
Bedroom 2	first	18.5	2.5	north, west, attic floor	18, 6-23 h
Bedroom 3	first	9.6	2.5	north, party wall, attic floor	18, 6-23 h
Bathroom	first	9.0	2.5	south, party wall, attic floor	22, 6-9 h and 19-22 h

Every room falls back to 16 degC outside its schedule. Four occupants, with the default occupancy gains of trano during the occupied hours of each room. Windows: 21.1 m2 (19 % of the floor area), 6.5 m2 of them facing the garden. The ceiling of the first floor is the floor of a cold, ventilated attic, modelled as a roof towards the outdoor air.

The party wall is an adiabatic wall (new, see below): half of the 19 cm brick wall, whose mid-plane is adiabatic because the neighbour is heated alike.

Envelope

Element	Before renovation	U [W/(m2.K)]	After renovation	U [W/(m2.K)]
External wall	brick cavity wall, 5 cm air cavity	1.47	+ 12 cm EPS (ETICS)	0.23
Attic floor	timber floor on joists	1.70	+ 22 cm mineral wool	0.15
Slab on ground	concrete and tiles	3.43 (slab), 0.71 (with the ground, ISO 13370)	+ 8 cm PUR	0.27 (slab), 0.20 (with the ground)
Windows	double glazing 4-12-4 air, wooden frames	Ug 2.88, Uw 2.71, g 0.76	triple glazing argon, two low-e coatings, insulated frames	Ug 0.70, Uw 0.80, g 0.47
Airtightness	n50 = 12 1/h (0.6 1/h of infiltration)		n50 = 3 1/h (0.15 1/h)

The glazings are described by their panes and gaps: trano computes U and g (EN 673, EN 410) for IDEAS from the same layers that Buildings uses, so that both libraries see the same windows. Air layers in opaque constructions are equivalent conductivities giving the EN ISO 6946 resistance of an unventilated cavity (0.18 m2K/W for 5 cm, 0.16 m2K/W between the joists).

Systems and sizing

The design heat loss follows EN 12831 (simplified): -8 degC outdoor (Uccle), the set points above, thermal bridges as +0.10 (before) and +0.05 W/(m2.K) (after) on the U-values, 0.5 1/h of natural ventilation before renovation, infiltration plus the supply air after an 80 % heat recovery after renovation, and the ground loss of the ISO 13370 model of IDEAS.

	Before renovation	After renovation
Design heat loss	10.75 kW (97 W/m2)	2.34 kW (21 W/m2)
Generator	non-condensing gas boiler, 16 kW (1.4 x the loss, reheat after the setback), efficiency 0.85 (lower heating value), 75 degC supply	air-water heat pump, 3 kW at -8 degC / 40 degC (1.25 x the loss), heating curve 40 degC at -8 degC to 30 degC at 16 degC outdoor, 100 l buffer
Emission	radiators rated 1.2 x the room loss at 75/65/20 degC, 13.2 kW in total, thermostatic valves (P control)	the same radiators: they cover the loss of every room from 39 degC supply
Ventilation	natural, by infiltration	balanced with heat recovery (system D), 150 m3/h (0.5 1/h), effectiveness 0.8, supply and extract in every room
PV	-	21 m2 of 20 % modules (4.2 kWp), south, 35 degrees

Room	Design loss before [W]	Design loss after [W]	Radiator at 75/65/20 degC [W]
Living	3239	815	3900
Kitchen	1446	355	1800
Bedroom 1	2059	387	2500
Bedroom 2	2078	396	2500
Bedroom 3	921	179	1200
Bathroom	1006	204	1300

Reference examples

The systems follow these examples of the libraries trano targets (IDEAS 3.0.0, Buildings 13.0.0):

IDEAS.Examples.PPD12 (a Belgian terraced house of about 120 m2): zoning, party walls as BoundaryWalls, radiators RadiatorEN442_2 rated at 75/65/20 degC, a gas boiler of 30 kW at 70 degC, balanced ventilation with a ConstantEffectiveness heat exchanger (0.75) and 300 m3/h.
Buildings.Fluid.HeatPumps.ModularReversible.Examples.AirToWater2D_OneRoomRadiator: the air-water heat pump (AirToWaterTableData2D, Vitocal 251-A data), its safety control (Wuellhorst2021, minimum on and off times) and its own condenser pump; trano's heat pump now follows it (see below).
Buildings.Examples.HydronicHeating.TwoRoomsWithStorage: BoilerPolynomial, radiators with two-way valves and balanced ventilation with heat recovery (0.9).
Buildings.Examples.Tutorial.SimpleHouse.SimpleHouse6: heat recovery ventilation (0.85).
Buildings.Electrical.AC.OnePhase.Sources (PVSimpleOriented): the PV array.

Neither library has a dwelling that combines a heat pump with PV: the after-renovation case is new.

Component mapping

The hydronic and ventilation systems of trano are built from Buildings components in the models of both libraries (the Trano package of every model); the envelope, the zones, the weather and the radiators come from the library chosen.

Component	trano YAML	IDEAS model	Buildings model	Reference	Supported
Zone	`spaces` (`infiltration` variant, `n50`)	`IDEAS.Buildings.Components.Zone`	`Trano.ThermalZones.MixedAirInf` (MixedAir + infiltration)	PPD12, BESTEST	yes
External wall, roof	`external_walls`	`IDEAS.Buildings.Components.OuterWall`	`datConExt`, `datConExtWin`	PPD12	yes
Window	`windows` + `glazings`	`IDEAS.Buildings.Components.Window` (U, g from the layers)	`datConExtWin` (layers)	PPD12	yes
Slab on ground	`floor_on_grounds`	`IDEAS.Buildings.Components.SlabOnGround` (ISO 13370)	`datConBou` + fixed temperature		yes (different ground models)
Party wall	`adiabatic_walls` (new)	`IDEAS.Buildings.Components.BoundaryWall` (adiabatic)	`datConBou`, open outer port	PPD12 `CommonWall`	yes (new)
Floors and walls between rooms	`internal_walls`	`IDEAS.Buildings.Components.InternalWall`	`surBou`		yes
Weather	`weather`	`IDEAS.BoundaryConditions.SimInfoManager`	`Buildings.BoundaryConditions.WeatherData.ReaderTMY3`	Uccle TMYx of IDEAS	yes
Gas boiler	`boiler`, `without_storage`	`Buildings.Fluid.Boilers.BoilerPolynomial`	same	TwoRoomsWithStorage, PPD12	yes (fixed)
Air-water heat pump	`boiler`, `air_water_heat_pump`	`Buildings.Fluid.HeatPumps.ModularReversible.AirToWaterTableData2D`	same	AirToWater2D_OneRoomRadiator	yes (rebuilt)
Radiators and valves	`radiator`, `valve` + `emission_control`	`IDEAS.Fluid.HeatExchangers.Radiators.RadiatorEN442_2`	`Buildings.Fluid.HeatExchangers.Radiators.RadiatorEN442_2`	PPD12	yes
Distribution	`pump`, `three_way_valve`, `split_valve`, `temperature_sensor`	Buildings movers and valves	same		yes
Heat recovery ventilation	`air_handling_unit`, `system_d` + `duct`s	`Buildings.Fluid.HeatExchangers.ConstantEffectiveness` + 2 `FlowControlled_dp`	same	PPD12, SimpleHouse6	yes
PV	`solar.photovoltaic`	`Buildings.Electrical.AC.OnePhase.Sources.PVSimpleOriented`	same	PVPanels	yes
Floor heating	-	`EmbeddedPipe`	`ParallelCircuitsSlab`		no (radiators used)

Changes to trano for these cases

The cases revealed problems in the existing models of trano, fixed along with the extensions:

Air-water heat pump rebuilt on the Buildings reference example: it could not start with Buildings 13 (swapped cooling temperatures), had no safety control and no condenser pump of its own, and drew its heat from a constant 10 degC source, so its water boiled when the radiator valves closed. It now charges a buffer through its own pump, follows a heating curve, keeps the library's safety control and takes the outdoor air as source (heat_pump_source_outdoor_air, true by default).
Boilers fire on heat demand only; the casing loss defaults to 0.5 % of the nominal power at 50 K instead of 5 % at 30 K; natural gas counts on its lower heating value for every variant.
Outputs on the data bus: electrical power and energy of the heat pump and of the ventilation fans (in the grid load), fuel power and energy of the boilers, heat delivered, supply and return temperatures, PV production.
Adiabatic walls (external_boundaries.adiabatic_walls) for party walls, in IDEAS, Buildings, the reduced-order and the ISO 13790 zones.
IDEAS ground model: average_indoor_temperature of a floor on ground sets the room temperature of the ISO 13370 heat flow of IDEAS (22 degC otherwise).
Same defaults in every library: the Uccle weather of IDEAS when none is given, the infiltration of the IDEAS zones (0.15 1/h) for the Buildings infiltration variant, and 21 degC as the default heating set point.

All of them are optional: models that do not use them only change where a default was wrong.

Results over a year

Both cases simulated over a year in OpenModelica 1.26 (IDEAS 3.0.0, Buildings 13.0.0) with the Uccle weather of IDEAS (11.1 degC mean). Energies are taken from the counters each element puts on the data bus; the heat of the radiators is integrated from their heat flows.

	Before, Buildings	Before, IDEAS	Difference	After, Buildings	After, IDEAS	Difference
Heat from the radiators [kWh]	14 420	14 910	+3.4 %	1 952	1 809	-7.3 %
Heating demand [kWh/m2]	130	135		17.6	16.4
Heat from the generator [kWh]	15 591	15 845	+1.6 %	1 992	1 844	-7.4 %
Gas, lower heating value [kWh]	19 188	19 361	+0.9 %	-	-
Heat pump electricity [kWh]	-	-		529	494	-6.6 %
Seasonal COP of the heat pump	-	-		3.77	3.73	-0.9 %
Ventilation fans [kWh]	-	-		224	224	0.0 %
Circulation pumps [kWh]	30	27		17	16
PV production [kWh]	-	-		4 644	4 645	0.0 %

The two libraries agree on the annual heating within 3.4 % before and 7.3 % after renovation, within the 10 % aimed at. Per room:

Room	Radiators before, Buildings / IDEAS [kWh]	Difference	Radiators after, Buildings / IDEAS [kWh]	Difference
Living	4 639 / 4 612	-1 %	806 / 757	-6 %
Kitchen	2 579 / 2 691	+4 %	607 / 561	-8 %
Bedroom 1	2 130 / 2 237	+5 %	67 / 54	-19 %
Bedroom 2	2 594 / 2 770	+7 %	157 / 140	-11 %
Bedroom 3	1 170 / 1 236	+6 %	46 / 38	-17 %
Bathroom	1 308 / 1 364	+4 %	267 / 258	-3 %

After renovation the bedrooms, at 18 degC, are kept warm by the rooms around them and by the supply air: their few tens of kWh differ by up to 19 % between the libraries without weighing on the total.

The renovation cuts the heat delivered to the rooms by 86 % (130 to 18 kWh/m2) and the final energy for heating from 19.2 MWh of gas to 0.53 MWh of electricity. With the fans, the house draws 0.75 MWh of electricity a year for heating and ventilation, against 4.6 MWh produced by the PV, most of it from April to September (see the tutorial for the monthly figures).

Known differences and limits

Ground. IDEAS computes the heat flow through the slab with the ISO 13370 model, from the exposed perimeter and the mean temperature of the room above; Buildings holds the outer face of the slab at a fixed temperature. examples/residential_cases.py sets that temperature so that both lose the same heat over the heating season. The IDEAS ground starts at 10.8 degC and takes about two weeks to settle: short simulations (the four January days of tests/test_residential_examples.py) differ more (within 15 % upstairs, 25 % for the house).
Comfort in the bathroom after renovation. The bathroom (22 degC, 6-9 h and 19-22 h, 16 degC otherwise) is below 21 degC during 43 % of its occupied hours in both libraries: the radiator kept from before the renovation warms it slowly from the setback with water at 30-40 degC. A lighter setback, an earlier start or a towel radiator sized for low temperatures would fix it; the case keeps the radiators on purpose. The other rooms are below their set point minus 1 K during at most 8 % of their occupied hours before renovation (the reheat after the setback) and 4 % after.
Boiler losses. BoilerPolynomial of Buildings 13 subtracts the loss of its casing twice from the water; trano sets that loss to 0.5 % of the nominal power at 50 K so that it stays small. Before renovation, 7.5 % of the heat of the boiler is lost by the boiler, the pipes and the valves before the radiators.
Air layers of opaque constructions are equivalent solid layers in both libraries (no convection or radiation across the cavity).
Natural ventilation before renovation is the infiltration of the zones, constant at n50 / 20; it does not vary with the wind or the temperature difference.