The need for energy-effective architectural and engineering design is becoming essential as the nature's limited resources are used more and more by modern developing technology. Constructing a building and organising its performance in a wise way can lead to significant economy of energy together with providing thermal comfort conditions to the house occupants.
The aim of this study is to analyse the Solar Decathlon House, designed by a student team, in terms of energy saving performance. The house model will be simulated in Ecotect specialized software to study the changes that can be made to improve the building to meet the Building Regulations requirements, in particular the PassivHause benchmarks. This report includes the research of key PassivHaus standards and key strategies to meet them. The house is situated in Madrid and experiences a specific climate, which is considered in the current project.
This report is suggested to be considered for further improvements in Solar Decathlon House design to meet the target energy consumption loads of the PassivHaus requirements.
Climate and Key Passive Strategies for the Site (Madrid)
Having chosen the building site in Madrid we need to be ready to face the critical weather conditions that appear in this continental climate. Though it is recognised to be hot and dry, there is a reasonable difference in day and night temperatures, reaching +36°C in the hottest month, July, in daytime and equalling only +13°C in the same month at night. Such instability can be used as a weakness as well as something we can benefit from during our project design. According to weather data analysis using the Ecotect Weather Tool and additional sources of information, the hot period, when the temperature reaches more than +25°C, starts with mid April and is over in October. According to the monthly diurnal averages, these months have a bigger day and night temperature amplitude, agreeably the air temperature difference. During this period, additional cooling to that we can provide with good insulation and wise planning will be essential. This is where night colder conditions can be used.
Relatively cold conditions are experienced in the period from October to May. In October and the two last spring months while the day temperatures can get to the level of +25 maximum, the night temperature value decreases rapidly and remains stable low in the range from 0°C to +5°C for the whole winter period. As the day temperatures are less then +20°C as well, the house has to work hard to keep it warm and will lose a large quantity of energy, saved and received during the daytime. Accordingly, this is the time when our house expects additional heating.
Thereafter, considering the fact that the heating period is about 7 months and the cooling is approximately 5 months or less, and taking into account that we can easily use passive cooling in summer, it can be predicted that the main energy consumption demand is the heating period.
Using the sun behaviour is one more passive technique we can use on our site. Considering that the site receives more sun radiation from the South during the underheated period and the most from the East during the overheated period, we have to avoid orientating bedrooms to the East, not to cause them gain heat during the summer days. The best glazing orientation for the winter period is the South, which can provide 2.10 kWh/m² of average daily sun radiation in accordance with the climatic data provided by Ecotect Weather Tool. This tool shows us the best orientation of the South facade to face 177.5° from the North, which means rotating the building 2.5° in the direction of the North to use as much passive heating for the underheated period as possible.
As the sun is critically intensive from the East, effective shading has to be provided to protect the East facade from overheating in summer, but, nevertheless, let the lower winter sun get in during the winter months.
The prevailing wind directions are mostly from the North, North-East, West and the South-West in summer. This information is essential to use for night summer cooling ventilation, as the windows can be opened and wind catchers can be used to let the cold air inside. The winter months experience rare but strong winds from the North and more continuous winds from the South-West, reaching the average air velocity of 20 km/h. These facades should be kept protected from winds. The both underheated and overheated seasons have less wind from the South-East. This fact requires attention in summertime, when night winds are welcome and overheating is to be avoided.
As the climate we are designing in is entirely dry and the relative humidity is far under the level of 60% during the time from March till October (the evidently hottest months), additional direct and indirect evaporative cooling is advised as one of the passive strategies.
We define that Madrid climate has a difference between the night and day air temperatures, and heat losses are estimated to be quite big in the winter night time; hence, we need to provide sufficient building materials, which could not be able to allow the heat in summer to enter the building easily and will keep the internal warmth during winter. In other words, the time lag of the external materials should be big enough, and the U-value - small, due to reliable insulation.
Taking into account that the average data we use for climatic analysis is not precise and the weather stations are usually located outside the city, so that they omit the "Urban Heat Island" (which is 2-3°C more than the temperature on the outskirts of the city), we need to consider the climate as a hotter and dryer with a less wind speed, due to the terrain effects.
As soon as we follow these passive techniques for using summer solar radiation wisely and preventing the house from overheating by using passive cooling techniques, as well as creating a well-isolated environment to keep the air warm inside in the period from November to April, we will be able to decrease energy use. Due to all the mentioned climatic opportunities the house in Madrid will be able to create thermal comfort conditions without using a great amount of extra expenses for energy.
Description of the Initial Variant of the House
To analyse the initial variant of the house according to the given plans and sections, a simplified model of the building has been created in Autodesk Ecotect Analysis software. Each room or set of interconnected open plan areas was defined as a separate thermal zone. The dimensions were taken from the internal part of the walls, roof, floors and ceilings as it is the actual space to be influenced by outdoor conditions after either wall, or door, or glazing insulation layer. Windows and doors were measured by only the glazing and partly the frame parts as those having different thermal properties from the walls and to have the actual number of sun radiation received by the room. As soon as the Ecotect window properties don't include the frame material, the glazing area would have been understood by the program as bigger than the real exposed to the sun glazing size.
The Ground floor eventually had 3 zones:
Zone one, uniting the living room, dining area, kitchen and utility, and the circulation area. The Zone has an entry from outdoors (to the courtyard) and one from the entrance lobby. Has three regular sized windows and two floor-to-ceiling windows, facing South-East side. Neither of the windows or doors are on the West façade.
The Zone has a void, connecting with the area of Zone seven.
Zone two is the entrance lobby, which has two outdoor entrance doors from the South (courtyard) and North, and one internal door, connecting the area with Zone one. The internal doors weren't taken into account in this analysis, though, as the main heat exchange processes happen between the outdoor and indoor areas and the zones influence each other as protective layers from those or that climatic or weather conditions.
Zone three unites the staircase (therefore has a void on the ceiling), provisional space for chiller, WC (water closet) and the plant room. It has a door, entering the provisional space for chiller from outside and is directly connected with Zone seven with the void. This zone as well as the Zone two, which is the entrance lobby, protect the building from the prevailing North and North-East winds.
The First floor resulted in 4 thermal zones:
Zone four is a bedroom, facing the South side with two windows.
Zone five is the bathroom, located above the entrance lobby, and has a window to the South, facing the courtyard.
Zone six is the second bedroom, which has a window to the North.
Zone seven is a complex of circulation all over the floor and is connected by two voids with the Ground floor, and has two roof lights.
The materials of all the building components, in other words, the construction specifications, were chosen according to the design team agreement, stated in the project brief and are the following. The thermal properties of each material are defined with the help of D 1.1 data sheet in "Introduction to Architectural Science" by Szokolay, S. V..
External Wall
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Timber Cladding
22.0
544.0
1220.0
0.115
2
Vapour Barrier
0.5
935.0
2301.0
0.414
3
Plywood
18.0
700.0
1300.0
0.138
4
Glass Fibre Quilt
50.0
12.0
840.0
0.040
5
Air Cavity
200.0
1.3
1004.0
5.560
6
Plywood
18.0
620.0
1300.0
0.138
7
Vapour Barrier
0.5
935.0
2301.0
0.414
8
Plasterboard
13.0
950.0
840.0
0.160
The initial variant external wall has a timber cladding facade and a number of insulation levels, such as vapour barriers and an air gap after a layer of glass fibre quilt. Among the others are plywood, between the insulation levels, and plasterboard facing the interior space.
The main characteristics we pay attention to meanwhile are the U-value, which equals 0.470 W/m²K, and the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786), 5.8 hrs.
Internal Partition
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Plasterboard
13.0
950.0
840.0
0.160
2
Glass Fibre Quilt
100.0
12.0
840.0
0.040
3
Plasterboard
13.0
950.0
840.0
0.160
The initial variant internal partition an insulation layer of glass fibre quilt between two layers of plasterboard.
The main characteristics we pay attention to meanwhile are the U-value, which equals 0.350 W/m²K (calculated by Ecotect), and the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786), 5.8 hrs.
Roof
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Bitumen/Felt Layers
1.5
1700.0
1000.0
0.500
2
Plywood
22.0
620.0
1300.0
0.138
3
Air Cavity
150.0
1.3
1004.0
5.560
4
Glass Fibre Quilt
50.0
12.0
840.0
0.040
5
Polyethylene Medium density
0.5
935.0
2301.0
0.414
6
Plywood
13.0
620.0
1300.0
0.138
The initial variant roof has a bitumen roof membrane outside layer and a number of insulation levels, such as polyethylene and an air gap before a layer of glass fibre quilt. Among the others are two layers of plywood, between the insulation levels.
The main characteristics we pay attention to meanwhile are the U-value, which equals 0.540 W/m²K, and the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786), 3.0 hrs.
Window
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Glass Standard
6.0
2300.0
836.8
1.046
2
Air Gap
30.0
1.3
1004.0
5.560
3
Glass Standard
6.0
2300.0
836.8
1.046
The initial variant window is double-glazed with an air gap of 30mm. Each glass layer is 6mm thick.
The main characteristics we pay attention to meanwhile are the U-value, which equals 2.710 W/m²K (calculated by Ecotect), which is a big value and means the heat exchange is quick in this structural material.
External Door
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Aluminium
2.0
2700.0
877.0
236.0
2
Polyurethane Board
50.0
30.0
1400.0
0.025
3
Aluminium
2.0
2700.0
877.0
236.0
The initial external door is made of two aluminium layers with a polyurethane board of 50 mm between.
The main characteristics we pay attention to meanwhile are the U-value, which equals 0.460 W/m²K, and the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786), 1.5 hrs.
Internal Floor
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Plywood
18.0
620.0
1300.0
0.138
2
Air Gap
150.0
1.3
1004.0
5.560
3
Plasterboard
13.0
950.0
840.0
0.160
The initial variant internal floor is a simple structure having an air gap between the upper floor plywood flooring and down floor plasterboard ceiling.
The main characteristics we pay attention to meanwhile are the U-value, which equals 1.760 W/m²K (calculated by Ecotect), and the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786), 2.2 hrs.
External Floor
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Plywood
22.0
620.0
1300.0
0.138
2
Polyethylene Medium density
0.5
935.0
2301.0
0.414
3
Air Cavity
100.0
1.3
1004.0
5.560
4
Glass Fibre Quilt
50.0
12.0
840.0
0.040
5
Polyethylene Medium density
0.5
935.0
2301.0
0.414
6
Plywood
22.0
620.0
1300.0
0.138
The initial variant external floor has a number of insulation levels, such as two layers of polyethylene after the first and before the last layer of plywood and an air gap before a layer of glass fibre quilt.
The main characteristics we pay attention to meanwhile are the U-value, which equals 0.520 W/m²K, and the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786), 3.5 hrs.
As the envelope of the building was created, the building's daily operation was investigated. To find out how this variant of the house is ventilated, according to CIBSE Guide A table 4.21, a target air change rate has been calculated. We assume our building as a leaky, as we have open-planned areas in the building, an ARC50 divisor and the permeability value to be 20m3/m2h at 50 Pa. To calculate the air change rate the following formula has been used:
A is the total floor area (103.562m²) of the building and V is its volume (193.974m³).
The wind sensitivity of the house is assumed to be 0.5, which means the house is somewhat sensitive to the wind.
To find out the comfort criteria in all the zones, we need to consider different activity level as well as occupants' clothing insulation level for every zone. According to the CIBSE Guide A table 1.5, in accordance with mentioned above, the following comfort conditions were suggested for summer and winter months:
Zones
Winter
Summer
Activity, met
Clothing, clo
Comfort t, °C
Activity, met
Clothing, clo
Comfort t, °C
Zone one
1.1-1.6
1.0
17-23
1.1-1.6
0.65
21-25
Zone two
1.4
1.0
19-21
1.4
0.65
21-23
Zone three
1.6
0.75
19-24
1.6
0.65
21-25
Zone four
0.9
2.5
17-19
0.9
1.2
23-25
Zone five
1.2
0.25
20-22
1.2
0.25
23-25
Zone six
0.9
2.5
17-19
0.9
1.2
23-25
Zone seven
1.6
0.75
19-24
1.6
0.65
21-25
In order to fix and simplify the comfort criteria in Ecotect we assume the comfort temperature to be in the area from 17 to 25°C in every zone according to above table, throughout the year. This appeared to be the lowest indoor comfort temperature in winter and the highest in summer for each zone. As the temperatures in Madrid vary from day till night dramatically, let us assume that the house has full air conditioning, by this we will know how much energy does the house consume if it is fully conditioned and doesn't use any environmental benefits (for instance, night cooling).
As any building has heat gains from the appliances and lightning it has, using the Table 6.7 (CIBSE Guide A), Appendix 6.A2 (CIBSE Guide A) the following assumptions for the basic internal gains have been made:
Zones
Type of Equipment
Number of appliances
Heat Gains (Watt)
Time of Operation (hrs)
Surface Area (m²)
Internal Gains (Watt/m²)
Zone one
Lights
Oven
Refrigerator
Dish Washer
Coffee Brewer
7
1
1
1
1
65
850
310
179
530
7
2
9
2
0.5
55.257
2.4
1.28
2.1
0.27
0.8
Zone two
Lights
1
65
1
3.663
0.74
Zone three
Lights
1
65
0.5
10.775
0.12
Zone four
Lights
PC
3
1
65
65
5
5
10.697
3.78
1.26
Zone five
Lights
2
65
3
5.616
2.89
Zone six
Lights
PC
3
1
65
65
5
5
8.099
5.01
1.67
Zone seven
Lights
3
65
1
9.45
0.86
Internal gains calculations have been made according to the formula:
Internal gains =
As well as internal gains from lights and equipment operation, the occupancy of the areas characterise how the dwellers use the building. The next graph describes the schedule of occupancy of Zone one, which is the living room and the kitchen with the dining room together on a standard weekday and weekend.
The next two graphs describe a supposed schedule of occupancy of Zone four, the parents' bedroom on standard weekdays and weekends.
According to these schedules we can identify the need for air conditioning. For example there's no need cooling a bedroom in summertime from 10 till 21 o'clock if it isn't used by occupants. That's why we define air conditioning only for occupancy hours in all the zones.
Analysis of the energy performance of the initial design of the house
As all the settings have been done and simulations have been run, we can now investigate the behaviour of the house to identify its weaknesses and strengths. Annual heating and cooling loads resulted in the following numbers:
MONTHLY HEATING/COOLING LOADS
All Visible Thermal Zones
Comfort: Zonal Bands
Max Heating: 2.934 kW at 01:00 on 15th Feb
Max Cooling: 6.671 kW at 13:00 on 31st Aug
MONTH
HEATING, kWh
COOLING, kWh
TOTAL, kWh
January
438.98
139.88
578.87
February
323.77
214.49
538.26
March
134.19
567.56
701.76
April
79.94
676.04
755.99
May
24.71
1094.25
1118.97
June
0
1814.07
1814.07
July
0
2210.64
2210.64
August
0
2165.38
2165.38
September
0.058
1463.73
1463.79
October
12.32
837.19
849.52
November
247.37
281.34
528.72
December
470.02
144.04
614.07
TOTAL
1731.4
11608.66
13340.07
PER M²
16.71
112.09
128.81
Floor Area: 103.562 m2
According to the monthly heating and cooling loads data, represented in the graph, the house has basically the need for cooling. The heating loads are comparatively low, though some heating is observed in the period from October till May.
If considering total gains throughout the year, the largest amount of heat is received from solar and internal gains, whereas heat losses take place due to ventilation and fabric. These are the weak sides of the building. The building demands cooling, this can be reached by reducing the internal gains and strong sun radiance and using ventilation in a regulated way. The fabric losses have to be reduced as well. As they are reduced and the U-value lessened at the same time when the time lag is increased, the building will be able to deal with the diurnal temperature difference.
The heat gains and losses according to different categories are compared in the following table.
GAINS BREAKDOWN - All Visible Thermal Zones
FROM: 1st January to 31st December
CATEGORY
LOSSES
GAINS
FABRIC
36.4%
2.0%
SOL-AIR
0.0%
2.1%
SOLAR
0.0%
31.2%
VENTILATION
58.8%
3.6%
INTERNAL
0.0%
60.8%
INTER-ZONAL
4.7%
0.4%
To find out whether the building can cope with the weather, it is efficient to analyse its behaviour in critical days of the year. For instance, the coldest and hottest day performance can reveal the weak zones we need to refer in the changed building to.
The coldest day is determined to be 12th January. The outside temperatures reach only 3 degrees below zero and are generally not higher than 4 degrees above zero. According to the graph, all the zones experience comfort temperatures during this day to a greater or lesser extent. Zone one and four, facing the South, appear to be the coldest, though. Even though, Zone one, which has the largest quantity of equipment, and, accordingly, internal gains, especially during morning time, shows a higher value of temperature after the morning appliance use (10am-14am). The warmest zone is that, surrounded by other zones and having a connection with the 1st floor - Zone three. At the same time, during the hottest day, which is assumed to be 31st July, when the temperatures rise up to 40 degrees above zero, the temperature of Zone one is artificially kept to be 25 degrees, as well as other zones except for the Zone two, which is exposed to both South and North sides.
Evident is the fact that in hot summer time almost all the zones use a large amount of energy to cool the room to reach at least the critical 25°C. Changes have to be done to lessen the amount of energy consumed at this time.
Fabric is the option that can be changed to prevent extra heat gains in summer and losses in winter time. As it can be seen on the Fabric gains graph, the materials that are used now in the house easily let the heat in when the weather conditions are hot. If the spring and autumn months can use the night cool from the fabric energy exchange, the summer months seem to be totally welcoming the heat during all the diurnal period. As well as fabric can be improved, the house tightness can be increased so that the house doesn't experience serious heat losses.
The heat losses values through fabric are achieved by using the formula: , where A is the area of element (m2), U is the U-value of the material (W/m2K), ti is the internal temperature and to - external. When comparing the two critical zones One and Three, which have different orientation and are planned in the way that zone one has mostly external walls, which expose the room directly to the outside weather conditions, and zone three is vice versa mostly surrounded by other zones and in this way is considerably protected, the heat losses value for both of the zones appears to have a large difference as well. When the heat losses for Zone one amount in 0.649 kWh, the same value for Zone three is 0.079 kWh on the coldest winter day.
Approximately the same situation happens with ventilation heat losses. The fabric and ventilation gain graphs appear to be very similar, which means the problem remains the same.
When we talk about ventilation heat losses, we consider a sufficiently protected envelope of the building, which will result in a high value of tightness, so that the heat losses will be lower. To estimate the mentioned value, the following formula is used: , where n is the air change rate (ach-1) and V - the room volume (m3). If comparing the results for the same two zones, the living room and kitchen zone will have 0.362 kWh of ventilation losses when zone three, the water closet and staircase area losses will amount in only 0.079 kWh on the coldest day.
Needless to say that solar radiation is one of the important factors to gain heat. The quantity of heat, received by the house will depend on a wide range of things, but the first and the most obvious is glazing. If we consider the window orientation of the building, we can clearly see that a large area of glazing is located on the south facades as well as facing the courtyard. By this structure designers aimed the building to gain maximum heat for winter months from the South and face a cooler area, the courtyard, in arid hot summer months. The West facade has no windows at all, taking into account that Western sun is the hottest. To compare the exposure to sun direct and indirect radiation and figure out the significance of solar radiation, the comparison of two, used to compare before, zones was held, Zone one and Zone three. First, totally exposed to the sun, facing the South, and hidden among other zones and facing the North, Zone three.
Represented above, the two pairs of graphs display solar radiation in the two zones. In particular, the two zones evidently differ in the means of received direct and indirect radiation. Zone One, mostly exposed to the sun has a large potential of receiving heat during winter months, at the same time remains dangerous when it goes about summer sun protection. The North facade Zone doesn't receive any direct solar radiation, but has an intense period of indirect solar gains, which can be used by locating windows in a way to catch the evening sun. All things considered, the building performance has to be compared with that of a passive one, for all the changes to be made in an effective way. The main points to consider are the fabric and ventilation losses, as well as solar exposure, orientation and internal gains. These are the weaknesses of the given house in Madrid and they are the first to be changed to design a low-energy house.
With reference to the PassivHaus benchmarks, the main principles of an energy-efficient house for a Madrid climate house are the following:
Heating/cooling less than 15 kWh/m² per year each;
Primary energy demand for heating, hot water and household electricity less than 120 kWh/m² per year;
U-value of the insulation layers of external components of building envelope less than 0.15 W/m²K;
Window U-value less than 0.8 W/m²K;
House envelope air tightness must not exceed 0.6 h-1 at a pressure of 50 Pa;
South orientation, shading - passive use of solar energy;
Heat recovery system (rate over 80%), which uses air-to-air heat exchanger;
Energy-saving household appliances.
According to the values the designed house in Madrid experiences, it doesn't meet the demands of PassivHaus standards. The total amount of energy used for cooling and heating reaches 128kWh/m², while it shouldn't exceed 15kWh/m² each. The equipment in the house isn't energy efficient and releases a large amount of heat, which leads to a serious demand for cooling during hot summer months. The window U-value in the initial variant of the house reaches up to 2.710W/m²K when according to the benchmarks the value should be close to 0.8W/m²K. The U-value for most of the external components has a value around 0.3-0.6 W/m²K, while the PassivHaus standards keep the U-value equalling the most 0.15 W/m²K. As well as that, the house doesn't use any heat recovery system and doesn't have any shading devices, though the orientation is chosen entirely in a right way. For this reason, a number of changes are advised to be made for the building to perform in an energy-saving way.
Description of the improved fabric specification and ventilation strategy
In order to improve the building's performance, some changes in its fabric, ventilation and equipment have been made. As the U-values didn't meet the standards of the PassivHaus construction energy-efficient strategies, described above, the layers and their thicknesses of especially external materials have been changed to meet the benchmarks. However, the use of standard glazing didn't allow the U-value to drop as low as 0.8 W/m²K, and reached 1.77W/m²K. It is seen as an improvement from the former 2.710W/m²K, but further low-emissivity glazing layers are advised to be considered for changing the value to a lower one. In other materials the U-value reached the values described in the benchmarks, reaching less than the critical value mentioned.
As the Inter-Zonal category of heat gains/losses in the initial variant of the house didn't influence the house performance much and reached the low number of 4.7% for losses and 0.4% for gains, the materials for the internal partitions and flooring were left as they were in the initial house specification.
The new envelope material properties are as follows:
External Wall
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Timber Cladding
22.0
544.0
1220.0
0.115
2
Vapour Barrier
0.5
935.0
2301.0
0.414
3
Air Cavity
150.0
1.3
1004.0
5.560
4
Timber
200.0
720.0
1680.0
0.140
5
Straw Board
200.0
310.0
1300.0
0.057
6
Timber
200.0
720.0
1680.0
0.140
7
Plasterboard
13.0
950.0
840.0
0.160
The initial U-valueof 0.470 W/m²K was changed to 0.14W/m²Kand the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786), from 5.8 hrs to 13. With this kind of properties, the building will remain cool in summer hot days and receive the heat from hot days during the cool night time.
Internal Partition
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Plasterboard
13.0
950.0
840.0
0.160
2
Glass Fibre Quilt
100.0
12.0
840.0
0.040
3
Plasterboard
13.0
950.0
840.0
0.160
The initial variant internal partition an insulation layer of glass fibre quilt between two layers of plasterboard.
The main characteristics we pay attention to are the U-value, which equals 0.350 W/m²K (calculated by Ecotect), and the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786), 5.8 hrs. These characteristics haven't been changed.
Roof
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Bitumen/Felt Layers
1.5
1700.0
1000.0
0.500
2
Plywood
22.0
620.0
1300.0
0.138
3
Polyethylene Medium density
0.5
935.0
2301.0
0.414
4
Glass Fibre Quilt
150.0
12.0
840.0
0.040
5
Air Cavity
50.0
1.3
1004.0
5.560
6
Glass Fibre Quilt
150.0
12.0
840.0
0.040
7
Polyethylene Medium density
0.5
935.0
2301.0
0.414
8
Plywood
13.0
620.0
1300.0
0.138
The U-value, which equalled 0.540 W/m²K in the initial variant of the house was changed to 0.120W/m²K, and the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786), from 3.0 hrs to 2.63.
Window
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Glass Standard
10.0
2300.0
836.8
1.046
2
Argon Glass
25.0
1.8
218.8
5.560
3
Glass Standard
10.0
2300.0
836.8
1.046
4
Argon Glass
25.0
1.8
218.8
5.560
5
Glass Standard
10.0
2300.0
836.8
1.046
The initial variant double-glazed window with an air gap was changed to a triple-glazed window with argon gas inside.
The main characteristics we pay attention to is the U-value, which equals 1.770W/m²K, but was reduced from the initial 2.710 W/m²K (calculated by Ecotect), which remains a big value, but can be changed with the help of adding low-emissivity layers on the glass.
External Door
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Oak
25.0
650.0
3050.0
0.230
2
Zink
5.0
7000.0
390.0
113.0
3
Steel
5.0
7800.0
480.0
45.0
4
Polyurethane Foamed
300.0
40.0
1674.0
0.032
5
Steel
5.0
7800.0
480.0
45.0
6
Zink
5.0
7000.0
390.0
113.0
7
Oak
25.0
650.0
3050.0
0.230
The U-valuewhich equalled 0.460 W/m²K in the initial variant of the house was changed to 0.1W/m²K, and the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786), from 1.5 hrs to 12.5.
Internal Floor
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Plywood
18.0
620.0
1300.0
0.138
2
Air Gap
150.0
1.3
1004.0
5.560
3
Plasterboard
13.0
950.0
840.0
0.160
The main characteristics we pay attention to are the U-value, which equals 1.760 W/m²K (calculated by Ecotect), and the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786), 2.2 hrs. These characteristics haven't been changed.
External Floor
#
Layer Name
Width
Density
Sp. Heat
Conduct.
1
Plywood
22.0
620.0
1300.0
0.138
2
Polyethylene Medium density
0.5
935.0
2301.0
0.414
3
Glass Fibre Quilt
200.0
12.0
840.0
0.040
4
Timber
200.0
720.0
1680.0
0.140
5
Plywood
20.0
620.0
1300.0
0.138
6
Polyethylene Medium density
0.5
935.0
2301.0
0.414
7
Oak
20.0
650.0
3050.0
0.230
The U-value, which equalled 0.520 W/m²K in the initial variant of the house was changed to 0.14W/m²K, and the thermal lag(defined with the help of excel document "Dynamic thermal properties calculator (ver 1.0)" based on ISO13786),from 3.5 hrs to 17.7.
As for the internal gains, the equipment has also been changed, resulting in the following table:
Zones
Type of Equipment
Number of appliances
Heat Gains (Watt)
Time of Operation (hrs)
Surface Area (m²)
Internal Gains (Watt/m²)
Zone one
C.F.Lights
Oven
Refrigerator
Dish Wash.
Coffee Br.
7
1
1
1
1
18
710
310
138
210
7
1
8
1
0.5
55.257
0.66
0.53
1.8
0.1
0.07
Zone two
C.F.Lights
1
18
1
3.663
0.2
Zone three
C.F.Lights
1
18
0.5
10.775
0.03
Zone four
C.F.Lights
PC
3
1
18
20
5
5
10.697
1.04
0.38
Zone five
C.F.Lights
2
18
3
5.616
0.8
Zone six
C.F.Lights
PC
3
1
18
20
5
5
8.099
1.38
0.51
Zone seven
C.F.Lights
3
18
1
9.45
0.23
The use of energy-efficient equipment has significantly decreased the level of internal gains per square meter in each zone. The lights have been changed to compact fluorescent lights, the refrigerator to a less-hour operation one, PCs to energy-saving mode and dish washer to a conveyor type one, as well as oven, releasing 710W. As soon as the changes have been made, the hours of work have been reviewed and eventually the oven and dishwasher operation hours were considered 1 hour less.
As was previously stated, the ventilation strategies have also been improved. After the changes have been made to the materials of external surfaces, it is claimed to be reasonably protected from the wind, so for the Ecotect simulation the number of 0.25ach instead of previous 0.5ach is chosen.
As a result of poor ventilation system, the initial variant of the building in Madrid lost 58.8% of heat. To improve the performance of the ventilation system, a heat recovery system has been implemented. Ecotect doesn't allow specifying a heat recovery system, though replacing the actual air change rate with an effective will conclude in a heat recovery system result. The amount of heat, recovered from the ventilation losses estimated an average 40% (though PH standard is 80%). Hence, the effective ACH is calculated as the following:
In our case, .
A heat recovery system requires an installation of a heat-recovery ventilator.
Analysis of the PassivHaus Variant of the House
If assuming the building has its air conditioning system (with a heat recovery system) on 24/7, and having taken into account the changes made to the house, including internal gains decrease and envelope material change, the energy analysis results have changed as follows.
The gains and losses have sufficiently decreased, which can be proved by the comparison of Gain breakdown graphs of the initial and changed variant of the house. The ventilation losses reached up to 0.8kWh/m² in the initial variant, whereas the improved variant shows the maximum result for the same category to be maximum 0.4kWh/m², which is twice as less. As well as ventilation losses, another weakness of the initial house, internal gains category, has improved to a less value. At first, the data was as large as 0.9kWh/m², while the new result indicates a maximum of 0.6kWh/m². The conduction characteristics of the envelope have reduced in number as well, being 0.15kWh/m²; whereas the initial values of this category reached as much as 0.25kWh/m². The Inter-Zonal gains and losses remain as low as they have been in the initial building design, though.
On the other hand, the results can be further improved by setting a timetable of the active system, providing cooling and heating, operation. As a research, a timetable of conditioning system operation was set to work only during the occupancy hours for every room and resulted in a much lower amount of energy consumption. The comparison of the three results, including the initial variant, the improved 24/7 conditioning and the improved with a set operation timetable, are described in the following graphs.
The percentage value of Inter-Zonal gains in the variant with a set operation timetable changes to a greater value, though, and reaches 15%, which means further improvements of construction materials can be made.
As soon as we compare the monthly heating and cooling loads with those of the initial variant, we can see a slight decrease in values from 128kWh to 102kWh total cooling and heating loads per m². The decrease is actually caused by the reduction in heating loads mostly. But if we consider the timetable of active conditioning system operation, a dramatic decrease can be easily noticed and reaches in total 42kWh per m². If referring to the PassivHaus benchmarks, which have a standard of 15kWh per m² per each cooling and heating (amounts 30kWh in total), it can be seen that the energy loads of the improved house are very close to the benchmark, having a difference only in 12kWh per m².
MONTHLY HEATING/COOLING LOADS (IMPROVED, 24/7 OPERATION)
All Visible Thermal Zones
Comfort: Zonal Bands
Max Heating: 1.356 kW at 01:00 on 15th Feb
Max Cooling: 4.662 kW at 13:00 on 31st Aug
MONTH
HEATING, kWh
COOLING, kWh
TOTAL, kWh
January
149.255
201.167
350.422
February
103.858
240.401
344.260
March
32.746
574.716
607.461
April
10.829
694.046
704.876
May
1.244
1024.001
1025.244
June
0
1446.971
1446.971
July
0
1661.810
1661.810
August
0
1622.314
1622.314
September
0
1259.456
1259.456
October
0.772
847.949
848.721
November
58.754
312.708
371.462
December
148.937
196.131
345.068
TOTAL
506.396
10081.670
10588.066
PER M²
4.89
97.349
102.239
Floor Area: 103.562 m2
MONTHLY HEATING/COOLING LOADS (OPERATION TIMETABLE)
All Visible Thermal Zones
Comfort: Zonal Bands
Max Heating: 1.1 kW at 01:00 on 15th Feb
Max Cooling: 4.597 kW at 13:00 on 31st Aug
MONTH
HEATING, kWh
COOLING, kWh
TOTAL, kWh
January
33.678
78.466
112.144
February
21.974
84.770
106.744
March
6.207
187.740
193.947
April
0.684
228.214
228.898
May
0.325
389.701
390.026
June
0
685.781
685.781
July
0
833.687
833.687
August
0
790.436
790.436
September
0
575.426
575.426
October
0.168
259.593
259.761
November
13.350
107.706
121.057
December
36.937
82.706
119.643
TOTAL
113.323
4304.226
4417.548
PER M²
1.094
41.562
42.656
Floor Area: 103.562 m2
According to the graphs, displayed above, an operation timetable for a conditioning system can sufficiently effect in saving of energy, no matter whether it is a heat recovery system or a regular one. In both ways a dramatic decrease in value proves the need for creating a schedule.
As a matter of fact, the numbers of cooling loads increase simultaneously with improving the fabric U-value at the same time when the heating loads decrease sufficiently.
The building's performance during the hottest and coldest days of the year remain the same, though, each zone experiences a temperature level of the comfort range and only Zone One doesn't have the increase in temperatures due to the morning use of kitchen appliances, that it used to have in the initial variant.
Though the orientation of the building had been changed to 2.5° counter clockwise, we can't see evident results of this minute change. Anyway, the optimum orientation suggested by Ecotect is aimed to lessen the amount of overheated period gains and receive maximum use from winter sun.
Strengths and Weaknesses of the Redesigned House, Suggestions for Further Improvements.
One of the most important advantages of the improvement that has been made in the house, located in Madrid, is the sufficient decrease in heating and cooling demands. Using both passive and active techniques at the same time made it possible to keep the indoor temperatures benefit from the cool nights and hot days by changing the envelope thermal characteristics. On the other hand, that resulted in an increase of the cooling loads and due to the amount of cooling demands, the cooling strategies can be improved in future changes of the house.
If we talk about the weaknesses of the house, it can be mentioned that the glazing, which occupies a large area on the South and East facades, attracts a big amount of solar radiation into the house. Due to this, cooling loads are greater than could have been when a reduction of solar radiation through glazing would have been made.
In general, the PassivHaus benchmarks prove their benefits to the modern energy-inefficient designs. Ecotect appears to be one of the effective tools, which helps to apply and analyse various techniques for the building to meet the mentioned standards. In other cases, the architectural design ideas as well as a precise material choice take responsibility for the building's performance.
There are though a number of drawbacks of the building and its computer simulation that can be improved. Firstly, the Autodesk Ecotect software simulation can be more precise if:
The walls were modelled including their thickness, to take into consideration self-shading that the building makes.
Shading devices on the South facades were modelled and the windows would receive less solar radiation.
The building had a more enhance climate-responsive design, such as adding the second roof for the heat to enter the house slowly during the hot days of summer.
The building had a more compact form, creating, possibly, a courtyard, closed from minimum 3 sides. This can be reached either by changing the form of the building, or adding some additional structures (like a wall, that was designed but not modelled in this simulation).
The air conditioning operation times were created in a more detailed way. That is actually the drawback of the program that we need to keep in mind.
As for the improvements of the design itself, including points that can be used in an Ecotect simulation as well, the following can be suggested:
Modern heat-recovery systems operate as efficient as recovering up to 95% of the heat. Hence, the more effective systems then those recovering 40% are suggested.
As the climate of Madrid is hot and dry in summer months especially, active and passive cooling is suggested. To add to those form changes mentioned above, a courtyard space can be created with a pool, which could provide passive evaporative cooling for summer months. As to active evaporative cooling, the system can be implemented in the ventilation ducts to cool the air, coming from outside, or wind catchers with an evaporative cooling option can be installed on the roof.
Replacing the shading devices, a PV system can be partly installed in the windows. That can create an interesting glazing design, that will make use of winter sun and shade the indoors (and make use as well) from the strong summer radiation.
The roof can be changed to a green one. These kind of roofs are not only visually attractive, but also energy efficient and make a passive evaporative cooling effect, though in winter they work as an energy, in other words, heat saving, layer. This kind of roof can also bring to naught the "Urban Heat Island" effect.
The roof, which is totally exposed to the sun, can also be used to hold PV (photovoltaic) as well as ST (solar thermal) panels, which can operate as a cooling system for the overheated period.
To conclude, the given building has a great potential of becoming a worthy example of a PassivHaus embedded technology. Improvements can be made both of passive and active techniques, though some of them can be hard or impossible to simulate in Ecotect. To say more, the climate can be considered at a closer view, as the weather data in Ecotect is usually gathered in a non-urban zone (airports, for instance). That is why some of the factors such as the "Urban Heat Island" or terrain and altitude effects on the wind speed and direction, which can be used for cooling needs, are not included in the computer simulation analysis.
