Introduction
Methodology
House and system description
Main parts | Components | Material | Thickness (m) |
U value (W/m-K) |
---|---|---|---|---|
Basement | Floor | 3 layers floor | 0.014 | 0.32 |
Tuplex | 0.003 | |||
Concrete | 0.060 | |||
EPS | 0.100 | |||
Concrete | 0.420 | |||
Internal wall | Concrete | 0.200 | 3.45 | |
External wall | Concrete | 0.220 | 0.26 | |
EPS | 0.100 | |||
First floor | Floor | 3 layers floor | 0.015 | 0.56 |
Tuplex | 0.001 | |||
Heat storage concrete | 0.210 | |||
EPS | 0.050 | |||
Concrete | 0.180 | |||
Internal wall | Plaster board | 0.013 | 1.44 | |
Ply wood | 0.009 | |||
Ply wood | 0.009 | |||
Plaster board | 0.013 | |||
External wall | Plaster board | 0.013 | 0.47 | |
Fiber glass | 0.012 | |||
Concrete | 0.190 | |||
Glass wool | 0.180 | |||
Brick | 0.070 | |||
Second floor | Floor | 3 layers floor | 0.014 | 1.02 |
Tuplex | 0.003 | |||
Plaster board | 0.030 | |||
Ply wood | 0.015 | |||
Plaster board | 0.013 | |||
Internal wall | Plaster board | 0.013 | 1.44 | |
Ply wood | 0.009 | |||
Plywood | 0.009 | |||
Plaster board | 0.013 | |||
External wall | Plaster board | 0.013 | 0.47 | |
Ply wood | 0.009 | |||
Glass wool | 0.184 | |||
Plywood | 0.009 | |||
Glass wool | 0.155 | |||
Glass wool Board | 0.025 | |||
Brick | 0.07 | |||
Others | Roof | Plaster board | 0.013 | 0.09 |
Glass wall | 0.419 | |||
Vent layer | 0.029 | |||
Plywood | 0.012 | |||
Tiles | 0.022 | |||
Entrance door | 1.00 | |||
Back door | 0.85 | |||
Window (Msora) | 0.68 | |||
Window (Velux) | 2.03 | |||
Basement window | 1.30 | |||
Sliding window | 1.10 |
House and system operation
First floor lighting
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Living areas: two 13 wattage and four 6.9 wattage; two 6.4 wattage are located in the stairs.
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Dining areas: seven 12 wattage (dining hall), one 13 wattage (dining area) and one 6.4 wattage (counter).
Second floor lighting
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Children’s room: eight 60 wattage.
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Hall: two 120 wattage.
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Stairs: three 75 wattage.
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Lavatory: two 40 wattage.
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Toilet: two 40 wattage.
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Bath tab: five 40 wattage.
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Emergency stair: two 20 wattage.
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Master bedroom: three 75 wattage and two 95 wattage.
System model
Component | Parameter | Value | Unit |
---|---|---|---|
Flat plate collector (Type 1): | Collector area | 12 | m2
|
Collector inclination | 45 | ° | |
Fluid specific heat | 4 | kJ/kg-K | |
(25 % propylene glycol) | |||
Tested flow rate | 120 | kg/m2-h | |
Intercept efficiency | 0.594 | ||
Efficiency slope | 16.2 | kJ/h-m2-K | |
Efficiency curvature | 0 | ||
Thermal storage tank (Type 60): | Tank volume | 0.37 | m3
|
Tank height | 1.4 | m | |
Tank perimeter | 1.82 | m | |
Height of water inlet | Tank bottom | ||
Height of water outlet | Tank top | ||
Tank loss coefficient | 0.92 | W/m2-K | |
Fluid thermal conductivity | 0.6 | W/m-K | |
(Water) | |||
Height of first HX inlet | 0.5 | m | |
(From bottom) | |||
Height of first HX outlet | Tank top | ||
Height of second HX inlet | 0.5 | m | |
(Below tank top) | |||
Height of second HX outlet | Tank top | ||
Height of third HX inlet | 0.5 | m | |
(Above tank middle) | |||
HX tube inlet diameter | 0.01 | m | |
HX tube outlet diameter | 0.012 | m | |
HX fin diameter | 0.022 | m | |
HX surface area | 1 | m2
| |
HX tube length | 20 | m | |
HX wall thermal conductivity | 401 | W/m-K | |
HX material conductivity | 401 | W/m-K | |
Water pump (Type 110) | Power coefficient | 1 | kJ/h |
Number of power coefficient | 1 | ||
Motor heat loss fraction | 0 | ||
Total pump efficiency | 0.6 | ||
Motor efficiency | 0.9 | ||
Water pipe (Type 709) | Inside diameter | 0.02 | m |
Outside diameter | 0.025 | m | |
Pipe length | 20 | m | |
(Collector loop, desiccant loop) | |||
Pipe length | 5 | m | |
(Auxiliary loop) | |||
Pipe thermal conductivity | 0.24 | W/m-K | |
Fluid thermal conductivity | 4 | kJ/h-m-K | |
Insulation thickness | 0.04 | m | |
Insulation thermal conductivity | 0.043 | W/m-K | |
Outer surface convective coefficient | 3 | kJ/h-m2-K | |
Back-up water heater (Type 659) | Rated capacity | 5 | kW |
Set point temperature | 65 | °C | |
Boiler efficiency | 0.8 |
Component | Parameter | Value | Unit |
---|---|---|---|
Air heating coil (Type 670) | Effectiveness | 0.8 | |
Desiccant wheel (Type 151) | F1 effectiveness | 0.235 | |
F2 effectiveness | 0.8 | ||
Enthalpy wheel (Type 667): | Sensible effectiveness | 0.8 | |
Latent effectiveness | 0.7 | ||
Heat exchanger (Type 760): | Sensible effectiveness | 0.85 | |
Ground heat exchanger (Type 557a) | Borehole deep | 15 | m |
Outer radius of U-tube pipe | 0.01664 | m | |
Inner radius of U-tube pipe | 0.01372 | m | |
Pipe thermal conductivity | 1.512 | kJ/h-m-K | |
Fluid specific heat | 4.19 | kJ/kg-K | |
Evaporative cooler (Type 757) | Secondary air flow rate | 1/2 of primary air flow rate | kg/h |
Component | Parameter | Value | Unit |
---|---|---|---|
Photovoltaic (PV) panel (Type 94a) | |||
PV panel Type No. 1 | Module size | 1535 × 280 | mm |
Number of module in series | 83 | ||
Number of modules in parallel | 1 | ||
Number of cells wires in series | 12 | ||
Module short circuit current | 5.4 | A | |
(Reference conditions) | |||
Module open circuit voltage | 13.3 | V | |
(Reference conditions) | |||
Reference temperature | 298 | K | |
Reference isolation | 1000 | W/m2
| |
Module voltage at maximum power point | 10.5 | V | |
(Reference conditions) | |||
Module current at maximum power point | 4.9 | A | |
(Reference conditions) | |||
PV panel Type No. 2 | Module size | 1228 × 280 | mm |
Number of module in series | 27 | ||
Number of modules in parallel | 1 | ||
Number of cells wires in series | 12 | ||
Module short circuit current | 5.4 | A | |
(Reference conditions) | |||
Module open circuit voltage | 9.7 | V | |
(Reference conditions) | |||
Reference temperature | 298 | K | |
Reference isolation | 1000 | W/m2
| |
Module voltage at maximum power point | 7.6 | V | |
(Reference conditions) | |||
Module current at maximum power point | 4.9 | A | |
(Reference conditions) | |||
Inverter (Type 48q) | |||
Efficiency | 0.88 |
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Thermal system
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Flat Plate Collector: Type 1a The component models the thermal performance of a variety of collector types using theory. This component is useful when you have technical specifications of the installed flat plate collector as in our case.
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Thermal Storage Tank: Type 60t The thermal performance of a water-filled sensible energy storage tank, subject to thermal stratification, can be modeled by this component. We utilized this type as our tank shown stratification based on our measurement.
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Auxiliary heater: Type 659 Model an external, proportionally controlled fluid heater. External proportional control (an input signal between 0 and 1) is in effect as long as a fluid set point temperature is not exceeded. If the set point is exceeded, the proportional control is internally modified to limit the fluid outlet temperature to the set point.
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Water pump: Type 110 This pump model computes a mass flow rate using a variable control function which is the actual situation of our system.
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Water pipe: Type 709 This component models the thermal behavior of fluid flow in a pipe or duct using variable size segments of fluid. It is very important to include water in the model to include the heat losses.
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Heat exchanger: Type 91 A zero capacitance sensible heat exchanger is modeled as a constant effectiveness device that is independent of the system configuration. We used this model as we know the effectiveness of our installed heat exchanger.
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PV system
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Photovoltaic panel: Type 94a A number of simulation options are available for this model. The first of these is the mathematical model used to predict the electrical performance of the array. The “four parameter” model should be used to for single crystal or polycrystalline PVs as in our case.
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Inverter: Type 48a In photovoltaic power systems, two power conditioning devices are needed. The first of these is a regulator, which distributes DC power from the solar cell array to and from a battery (in systems with energy storage) and to the second component, the inverter. The inverter converts the DC power to AC and sends it to the load and/or feeds it back to the utility.
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HVAC system
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Desiccant wheel: Type 151 This is a modified model of the Type 683 component of a rotary desiccant dehumidifier containing nominal silica gel whose performance is based on equations for F1–F2 potentials.
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Sensible wheel: Type 667c Uses a “constant effectiveness—minimum capacitance” approach to model an air to air heat recovery device in which two air streams are passed near each other so that both energy and possibly moisture may be transferred between the streams.
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Air–water heat exchanger: Type 670 Model a heating device in which air is passed across coils containing a hot liquid. The air exits hotter and at the same absolute humidity ratio as it entered the device. The user specifies the air inlet and liquid inlet conditions.
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Evaporative cooler: Type 757a Model an evaporative cooling device for which the user supplies the inlet air conditions of a primary and secondary air stream and the device effectiveness as a function of primary stream inlet air dry bulb temperature and secondary stream inlet air wet bulb temperature.
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Air-to-water heat exchanger: Type 91 A zero capacitance sensible heat exchanger is modeled as a constant effectiveness device that is independent of the system configuration.
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Borehole heat exchanger: Type 557a This models a vertical heat exchanger that interacts thermally with the ground. This ground heat exchanger model is most commonly used in ground source heat pump applications. In typical U-tube ground heat exchanger applications, a vertical borehole is drilled into the ground. A U-tube heat exchanger is then pushed into the borehole.
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House and system evaluation
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Biomass water heater: the mass requirement for biomass (wood pellets) is based on the lower heating value (LHV) of 3100 kWh/m3. The wood pellets density is 650 kg/m3. The price of wood pellets is based on the US$0.90/kg [34]. The biomass is considered negligible of CO2 emission as it is considered bioenergy in this study [35]. Bioenergy means that the amount of CO2 emitted during biomass combustion is enough to grow the biomass sources.
Analytical formulation
Results and discussion
Air conditions
Electricity cost and CO2 emission
PV installation
Water heater fuels
Case analysis
Case 1a
| Case 2 | Case 3 | Case 4 | Case 5 | Case 6 | |
---|---|---|---|---|---|---|
Flat plate collector | ||||||
Area (m2) | 12 | 16 | 20 | 20 | 20 | 20 |
Thermal storage tank | ||||||
Volume (m3) | 0.37 | 0.74 | 1.1 | 0.74 | 1.48 | 0.74 |
Photovoltaic panel | ||||||
Panel 1(m2) | 36.1 | 72.2 | 72.2 | 72.2 | 72.2 | 72.2 |
Panel 2 (m2) | 9.6 | 19.3 | 19.3 | 19.3 | 19.3 | 19.3 |
Geothermal heat exchanger | ||||||
Installation | No | No | No | No | No | Yes |
Conclusions
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The alternative energy and technology supported house consumed 52 GJ/year based on the energy for the air heating, desiccant regeneration, domestic hot water, electric lighting, electric appliances and auxiliary electricity for the HVAC system. The gathered information of the houses in the region is almost 65 GJ/year [42]. Please be aware that this model house is larger than the typical houses in the region by around 15–20 %. Even with this, the house still has lower energy consumption.
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The energy consumption per floor area of the house is 371 kWh/m2-year without considering the floor areas for the toilets, showers and stock rooms. The lower consumption of the house of 22.22 % difference with respect to the houses in the region [42] is due to good insulation, air tightness, energy efficient lighting and a new desiccant-based HVAC system. Even with 22.22 % difference, the house mentioned in this paper is still more economical and environmental friendly during the operation as most of the energy consumed came from the energy supported by solar energy and biomass.
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The installation of the photovoltaic roof tiles has a great impact on electricity cost saving resulting in a 75 % saving from grid line electricity consumption. In addition, it contributes to the reduction of the carbon dioxide emission of the house due to the minimization of grid line electricity consumption.
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An alternative water heater provides both economic and environmental benefits to the house by reducing the house heater consumption cost by almost 80 %. Also, it makes the water heating operation zero carbon dioxide emission when a biomass source is considered as biofuel.
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Case studies show that increasing the size of the installed photovoltaic roof tiles or maximizing the available roof area (almost the same to the size of the south facing roof) makes the house an energy generating home (EGH), as well as a negative carbon emission home (NCEH). This is possible when the water heater is supported by biomass fuel.
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Using desiccant dehumidification with evaporative cooling of supply air is not enough to support the cooling in peak summer days due to its limited capacity in air dehumidification for further indirect evaporative cooling. The application of borehole heat exchanger to cool the dehumidified supply air can provide the house cooling requirement during the peak summer season.