Single-zone emulator (by University of Southern Denmark, modified by SINTEF)

General model description


Building Design and Use

The overall description of the actual building can be found in the following paper: M. Jradi et al., A World Class Energy Efficient University Building by Danish 2020 Standards, Energy Procedia 132 (2017), 21-26. Some of validation reference data are taken from this paper directly. The following documentation contains only information relevant for the simplified model included in BOPTEST. Additional details regarding the simplified building validattion can be found in the following paper: T. Tang et al.,Implementation and performance analysis of a multi-energy building emulator, In Proc. of 2020 6th IEEE International Energy Conference (ENERGYCon), Sep 28 - Oct 1.

Architecture

The building surface area is 8500 m2. There are 3 above-ground floors containing classrooms (40% of floor area), study zones (25%), offices (15%), and common spaces (20%). There is also a basement level containing main HVAC facilities and the main heat exchanger connected to district heating. The building can accommodate around 1350 people.

Constructions

The building thermal envelope is comprised of three different opaque constructions: ground floor (floor), external wall (extWall), and roof (roof). The internal walls are modeled by a single-layer generic construction representing medium-weight partitions. All opaqua construction layers and thermal characteristics are described in Table 1. All windows are modeled using the same contruction type, based on a triple-glass window model from the Buildings library (Buildings.HeatTransfer.Data.GlazingSystems.TripleClearAir13ClearAir13Clear), with the following layers: triple pane, clear glass 3mm, air 12.7 mm, clear glass 3mm, air 12.7 mm, clear glass 3mm.

Table 1: Opaque constructions and their thermal parameters (x - width [m], k - conductivity [W/(mK)], c - specific heat [J/(kgK)], d - density [g/cm3])

Construction

Layers

Parameters (x, k, c, d)

floor

Concrete

0.2, 1.4, 840, 2.24


Insulation

0.15, 0.04, 1000, 0.05

extWall

Concrete

0.2, 1.4, 840, 2.24


Insulation

0.27, 0.04, 1000, 0.05

roof

Concrete

0.27, 1.4, 840, 2.24


Insulation

0.52, 0.04, 1000, 0.05

intWall

Generic material

0.15, 0.5, 1000, 0.25

Occupancy schedules and comfort requirements

The building is equiped with camera-based sensors that estimate real-time occupants number. Occupancy data is extracted from our internal database"Volta" and stored in "occ.txt" file in the model. Comfort requirements are defined as indoor thermal comfort (temperature) and CO2 concentration, with the temperature setpoint as 21°C during occupied hours (7 AM to 7 PM on weekdays) and 15°C otherwise and CO2 concentration upper limit as 800ppm.

Internal loads and schedules

Internal heat gains only consider heat from occupancy. It is assumed that the internal gain per person is 120W and it is evenly distributed over the floor area (i.e. 120 W / 8500 m2). The heat generated per occupant is divided as 40% radiant, 40% convective and 20% latent heat.

Climate

The weather data is based on Copenhagen Typical Meteorological Year. The weather file is located in modelica://OU44Emulator/Resources/Weather/DNK_Copenhagen.061800_IWEC.mos.

HVAC System Design

The actual building is equipped with 4 balanced Air Handling Units (AHU) with heat recovery wheels and pre-heating coils (Fig. 1) and each room is equipped with radiator heating. The heating is provided by district heating grid. Since the model is a single-zone model, all AHUs are modeled with a single AHU oversized by a factor of 4, and all radiators are modeled with a single radiator. The following description covers the HVAC design as implemented in the model, and not the HVAC system in the actual building.

Ventilation

The AHU contains two identical fans, one for supply air and one for extract air.

Figure 1 shows a principle flow sheet for the air handling unit (AHU), as modelled in the emulator. It shows the placement of the sensors and components and the control principle.

Figure 2 shows the fan characteristics. The grey line shows the operational point at nominal speed. Same fan model is used for both supply and extract fans.

Fig. 1: Principle ventilation flow sheet.

Fig. 2: Fan characteristics.

Hydronic heating system

The layout of the hydronic heating system is shown in Figure 3. Piping segments are modelled between the main distribution pipes and the control valves for both the ventilation and radiator circuits. Piping segments includes heat loss to a fixed external temperature of 20 °C.

Heat is supplied by a district heating system. The temperature of the district heating is fixed to 65 °C. The supply temperature of the hydronic heating system is controlled by the flow on the primary side of the district heating heat exchanger. The setpoint follows the outdoor temperature compensation curve shown in Figure 4.

The main circulation pump sustains a fixed pressure across the distribution pipes. The baseline setpoint is 50,000 Pa. This is also the maximum possible pressure difference of the pump.

The control valve of the radiator tracks the measured indoor temperature. The baseline controller implements a night setback of 3 K outside of operating hours. After night setback, the setpoint is reset to 22 °C 2 hours before the next operating hour (4 hours on Mondays), to make sure the building has reached the setpoint temperature before the building is occupied again.

Fig. 3: Hydronic heating system as modeled.

The design specifications of the heat exchangers are given in Table 2.

Table 1: Design specification of heat exchangers

System Nominal Capacity [kW] Tin_hot [°C] Tout_hot [°C] Tin_cold [°C] Tout_cold [°C]
District heating 500 65 45 35 55
AHU coil 250 55 35 14 20
Radiator 255 55 35 21 21

Fig. 4: Baseline controller outdoor temperature compensation curve.

Model IO's

Inputs

The model inputs are:

Outputs

The model outputs are:

Forecasts

The model forecasts are:

Additional System Design

Lighting

Lighting is not considered in the model.

Shading

The model assume there is no shading in the building.

Onsite generation and storage

There is no onsite power generation or energy storage in the model.

Model Implementation Details

Moist vs .dry air

The model uses moist air despite that no condensation is modelled in any of the used components.

Pressure-flow models

A circulation hot water loop is used to model the heating emission system.

Infiltration models

Inflitration is modeled with a fixed ACH parameter (0.2) in addtion to imbalance between supply and extract air flow.

CO2 models

CO2 concentration of the zone is included in the model. We introduce a scale factor of 4 for occupancy CO2 generation to calibrate control of the AHU with real building operation, since the model is lumping unoccupied zones with occupied zones that would drive AHU usage in real building operation.

Important Model Implementation Assumption

The major assumptions are as follows:

Scenario Information

Time Periods

The Peak Heat Day (specifier for /scenario API is 'peak_heat_day') period is:

The Typical Heat Day (specifier for /scenario API is 'typical_heat_day') period is:

Energy pricing

Energy Price consists of electric power price and district heating price.

Electric power price:

Distric heating price=0.0828 euro/kWh,source:https://www.c40.org/case_studies/98-of-copenhagen-city-heating-supplied-by-waste-heat

Emission factors

Two emission factors are considered based on Danish scenario:

Weather Forecast Uncertainty: Temperature

Options for /scenario API are 'low', 'medium', or 'high'. Empty or None will lead to deterministic forecasts. See the BOPTEST design documentation for more information.

Weather Forecast Uncertainty: Global Horizontal Irradiation (GHI)

Options for /scenario API are 'low', 'medium', or 'high'. Empty or None will lead to deterministic forecasts. See the BOPTEST design documentation for more information.