Serial 1.5D models
6.3 Test mock-up
6.3.1 Design
Before describing the design in detail, notice that the mock-up is part of an on-going project sponsored by ELFOR (the Danish union of electricity distributing companies) to investigate the introduction of thermo active components in the Danish building industry. This project is still in an early phase, and therefore the measurements in the mock-up are preliminary in the sense that at the time of the finishing of this thesis, the mock-up has not been completely finished. The influence of this will be described where appropriate. However most
importantly, the measurements are well suited for validation of TASim, which is the main interest in this context. The final results from the measurements in the mock-up will be published during 2005.
General description
The main design of the mock-up is a construction consisting of two levels of thermo active components in between which an office room in a building is placed. The room is closed to the four sides by insulating walls. The room is surrounded by a guard box, which separates the room and thermo active component from the rest of the laboratory.
The room has a length of 6.0m and a width of 3.6m, for a total room area of 21.6m²,
equivalent to a fairly large single person office or a “typical” two-person office. The internal room height is 3.6m. The decks are 6.6m in length, so that they are long enough to be
supported by the load bearing construction (described below). The lower deck is raised about 0.5m from the floor in the laboratory. The upper deck is about 4.4m above the laboratory floor.
The total size of the mock-up is 7.6m long, 4.6m wide and 5.4m high.
Two levels of thermo active components have been used to ensure that the room will have a deck with realistic conditions both above and below the room itself. The dimensions of the deck are identical to those in Figure 6.1. That is the deck is 270mm high, 1200mm wide and 6600mm long. The deck has seven cavities with a distance of 150mm. The height is of the cavities is 160mm and the width is 108mm where it is widest. Below each of the cavities a 20mm PEX-pipe is integrated in the concrete. The centerline of the pipe is 50mm above the ceiling surface.
In the test version, individual strings of pipe will be integrated in the deck, which will be connected after creating the deck. A later version will most likely have the pipe placed as a serpentine in the deck.
The ends of the decks have been insulated to minimize unwanted heat losses from the deck to the guard. The temperature in the guard zone will in all cases be controlled to be the same as in the room, to ensure that there will be no heat transfer across the room walls. The air gap in the guard zone will also allow realistic thermal conditions for the deck surfaces facing the guard. However, the radiation is not going to be completely realistic due to small vertical distance between deck surface and guard surface. For the measurements in this work, the thermal guard has not been finished, and therefore the guard temperature has not been controlled. Where this has an influence on the results this will be stressed.
The decks are supported by a load bearing construction placed in the air gap in the guard, designed as four steel columns with beams for supporting the deck-elements. To ensure that the supporting beams will have a minimal influence on the temperature distribution in the deck, a 100mm x 100mm wooden beam is placed on top of the steel beam as a thermal break.
Approximately 50 thermocouples and thermopiles are measuring the temperatures throughout the construction.
The flow in the decks is controlled by two flow units capable of delivering water at a given temperature and flow. The flow units can be turned on or off at a given time schedule to give dynamical conditions for the flow.
Internally in the room, four radiators with a total power output of 1.9kW are installed as heat load. The maximum heat load in the room is therefore 88W/m². The internal heat load is controlled by a power controller which is fed by a continuous 0-10V signal. Therefore for instance, a 5V signal means that the radiators are turned on 50% of the time, resulting in a heat load of 44W/m². The heat load can be controlled, in principle, infinitely variably.
The guard will be controlled by the same type of control, once this has been installed.
In the room, there is no ventilation in the present state of the mock-up. The inner walls and joints between walls and decks have been carefully assembled to avoid leaks.
The measurement and control of the conditions in the mock-up is integrated in a LabVIEW (National Instruments, 2003) application.
Figure 6.15 and Figure 6.16 shows the main dimensions of the mock-up seen from the side and horizontally.
3,6 m Deck
Deck 5,4 m
Figure 6.15 Main overview of dimensions in a vertical view of mock-up seen from the side.
7,6 m
4,6 m Room:
3.6 x 6.0 m
Figure 6.16 Main overview of dimensions in a horizontal view of mock-up seen from above.
Pictures of the construction
To give a better idea about the construction, a few pictures from the construction phase are shown.
Figure 6.17 shows the load bearing construction and the lower deck. Notice the wooden beam placed between the deck and the load bearing steel beam which will break the thermal bridge.
Both the lower and upper deck are made from three decks, each with a width of 1.2m for a total of 3.6m.
Figure 6.17 Pictures of the load bearing construction and the lower deck after installation.
Figure 6.18 shows two close-up pictures of the end of the deck. The left picture shows the deck. The pipes are placed directly under each of the cavities and they have not been assembled. This is shown in the right picture where the pipes have been connected as a serpentine layout for each of the three decks which are each fed from a manifold. The picture shows the insulated supply pipe where the supply temperature and warm side of the
temperature difference between supply and return are measured, through which the
distributing manifold pipe is fed. Further the insulation of the side of the deck can be seen.
During the measurements, the box at the end of the deck is insulated.
Figure 6.18 Pictures of the end of one of the decks. The left picture shows the deck without the pipe connected, and the right figure shows the deck with manifold.
Figure 6.19 shows the finished insulation box at the end of the deck. The inner wall between room and guard can also be seen.
Figure 6.19 End of upper deck after being finished. The wooden box is filled with insulation thereby minimizing the unwanted heat loss from end of deck and manifold. All four deck ends (upper and lower) have the same insulation box.
Figure 6.20 shows the floor construction in the room. This is constructed as a wooden floor on rafts placed on the concrete deck. In the room, the floor construction is finished by a 6mm parquet floor to make a “nice looking” finish in the room. This has not been installed in the upper deck, as this will not be visible.
Figure 6.20 Floor construction. A wooden floor on rafts is used. A plywood plate of 15mm is used as the floor covering. In the room, a 6mm parquet floor is placed on top of the plywood plate.
Figure 6.21 shows the room after being finished. The pole in the middle of the room is used for air temperatures and the partly hidden pole is used for measurement of operative, radiant and air temperatures as well as air velocity and relative humidity. The picture also shows two of the four radiators with a nominal power output of 500W. These are placed approximately in the middle of each of the walls about 200mm from the floor.
Figure 6.21 Room. Four 500W heating panels (two can be seen here) are installed on each wall. Centrally in the room, measurements of temperatures (air, radiant and operative) are performed as well as air velocity and relative humidity.
Measurement equipment
The temperatures in the mock-up are measured by the use of thermocouples for absolute temperatures and thermopiles for temperature differences. Type TT thermocouples (cupper/constantan) are used. Type TT has an increased accuracy compared to type T. An Agilent 34970A data acquisition/Switch unit equipped with 60 voltage and 6 current measurement slots connected to a PC is used for the measurements.
The temperatures are calculated internally in the instrument by using ITS-90 software compensation.
The accuracy of the temperature measurements can be found from the following relation:
(
%of reading+%of range)
±
=
Accuracy (6.5)
This accuracy is very good for the measurement of voltage and conversion of voltage to temperature to temperatures. However, the accuracy of the thermocouple itself is not as good.
An accuracy of ±1K is given in the data sheet for the data logger, plus the accuracy from the thermocouples themselves, which are expected to be 0.3% of the reading. This is typical for thermocouple measurements. A very large part of this is due to the fact that a common reference point in the data logger is used. Since the temperature across this data logger board can be up to 1K, this sets the limit to the accuracy.
For the voltage differential measurements (thermopiles), which do not use the reference point in the data logger, the coefficients in Eq. (6.5) for the measurement accuracy are
0.0050+0.0040. Notice that for the thermopiles, three or five elements in the pile are used to increase the measurement signal. This increases the accuracy of these measurements.
The flow is measured using a “Danfoss MASS 1100, DN10” which can measure up to 4.400 kg/h. The output from the unit is a 0-20mA signal, where the maximum rate which will give 20mA can be set on the unit. An accuracy of ±0.5% is given on the output of the signal. The accuracy of the reading in the data logger, the coefficients are 0.050+0.005.
The accuracy of the heat flow in the decks is a combination of the flow measurement and temperature difference measured by the thermopile placed in the supply and return of the decks (see right side of Figure 6.18 for position of the supply side of the thermopile). In a
previous investigation (Weitzmann and Jensen, 2000), the error has been shown to be less than 2% of the actual heat flow.
For the measurement of operative temperature, radiant temperature, air velocity and relative humidity, Brüel and Kjær 1212 and 1213 have been used. For the operative temperature the accuracy is ±0.5K. At the same time, there is an offset error in the device, which has been found by calibrating it using a digital precision thermometer. Here the offset was found to be 0.4K, meaning the device measures too high operative temperature.
Control systems
The control of the radiators in the room is controlled by a Measurement Computing PCI-DAS6014 control and measurement board, which is integrated in the PC. The board sends a 0-10V signal to an electronic analog power controller from IC Electronic. This power
controller is using a ‘Burst Firing mode’, which is in practice a switch which will ensure that the power controller will supply power to the radiators in the part of the time decided by the control signal. Therefore a 5V signal means that the radiators are turned on for 50% of the time.
The temperature in the room is controlled by a PID-control of the heat supply to the radiators in case of steady state measurements and a fixed signal when a fixed heat supply to the radiators is required.
The temperature in the guard is controlled to be identical to the room temperature. This has however not been included in these measurements since the guard walls have not been installed for the measurements.
Measurement positions of temperature
Figure 6.22 shows the temperature positions in the upper deck. Three sections are used, with a different number of measurements in each section. The positions of the sections are shown on the horizontal view. Section 1 is the most detailed, where temperatures are measured in different positions of the deck and on the upper and lower surface of the deck. The temperatures in four internal positions are measured. In all sections, the temperature difference across the floor covering has been measured to find the heat flow. A thermopile with three elements is used in each of three sections. For the lower deck, only one temperature on the lower surface is measured. Otherwise the same positions are installed here.
Section 1 - middle of deck
525 mm
Section 2 - assembly between two decks Section 3 − ∆T Thermocouple
Thermopile
Thermocouple Thermopile Thermocouple
Thermopile
Section 1
Section 3 Section 2
6m
3.6mm
Horizontal view of deck showing measurement sections
Figure 6.22 Measurement positions in the decks for the three measurement sections. The horizontal view shows the position of the measurement sections, while the vertical views show the actual placement.
Figure 6.23 shows the measurement in the room. The left figure shows the internal surface temperatures. The floor and ceiling surface temperatures are measured in the middle of the surface. On one of the 6m long walls, the surface temperatures are measured at heights of 0.5m, 1.5m, 2.5m and 3.5m. Initially, a test has shown that measuring the temperature in the middle of each of the surfaces gave almost identical surface temperatures, which means that there is no need to measure all four. The right figure shows the air temperature measurements, which are measured at 0.1m, 0.7m, 1.1m, 1.8m and 3.5m (0.1m from the ceiling surface).
Surface temperature
½
3,6 m 3,6 m
6,0 m
Front wall 3 Wall 1
Wall 2 Wall 4
0,5 m 1,5 m 2,5 m 3,5 m
Vertical view 0,1 m
0,7 m 1,1 m
0,1 m
Air temperature 1,8 m
Figure 6.23 Measurement positions in room.
Figure 6.24 shows the control measurements of the temperatures and temperature differences characterising the conditions between room and guard. The measurement positions shown on the left figure are used to find the surface temperature of the end of the deck. The middle figure shows the measurement positions for the temperature difference between the rim of the deck and guard. Finally, the right figure shows the measurement of the temperature difference across the inner walls. One thermopile is installed in each of the four walls.
0,27 m
0,10 m
Thermocouple
Thermocouple Thermopile
Thermocouple Thermopile
0,10 m
Figure 6.24 Measurement positions between room and guard.
Measurements of flow and temperatures in water loop
Figure 6.25 shows the measurements used for the flow and temperatures in each of to the two decks. The flow is measured in the flow unit while the supply temperature is measured directly at the inlet to the distribution manifold to each of the decks. The temperature
difference is measured by a thermopile placed in the inlet and outlet from the manifolds. The same setup is used for both decks.
Return Notice: not drawn to scale Supply
Thermocouple Thermopile Flow
Flow unit
Figure 6.25 Measurement positions used for flow measurement
Heat load in room
The heat load in the room is found from the control signal to the power control units. The following conversion is used, which has been found by measuring the integrated energy consumption for approximately 5-10 minutes for each measurement point while applying the control signal. Based on this, the average heat load during the integration period has been calculated resulting in a linear relation, which is shown in Figure 6.26.
0 1 2 3 4 5 6 7 8 9 10
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Signal [V]
Heat load in room from radiators [W]
Conversion between control signal and heat load in room
Figure 6.26 Conversion between control signal to power control unit and heat load in room
Using a linear fit, the following correlation between control signal and heat load in the room:
signal
room V
q =191.3⋅ [W]
or
signal
room V
q =8.86⋅ [W/m²]
(6.6)
This correlation is used for finding the internal heat load in the room. Notice, that when the control signal is 10V, the heat flow rate to the room is only around 1900W instead of 2000W which is the nominal heat load.
A long term comparison spanning two days of measurements between the calculated energy consumption based on the control signal and an integrated measurement shows a deviation of around 2% between measured and calculated heat flow.