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Sustainable Building Design - Coggle Diagram
Sustainable Building Design
Is...
Intended to provide confort without using too much resourses by using design
Important for saving money, avoid depleting natural resourses and fighting global warming
All humans had to passivally conditionate the air of buildings before the invention of HVAC
Important concepts
Energy use in buildings
Can be analysed with detail and benchmarked
Energy Use Intensity (EUI) - kWh/m² year or kBTU/ft² year - metric to measure energy eficiency, due to its limitions, better used with in similar biudings
Certifications can be used to indentify and promote energy efficient builldings - EED Cerfitied Buildings is the most common in the US. Other example: Energy Star
Can be devided in...
internal loads (other uses)
conditioning loads (air conditioning)
Is big part of all energy consuption, with transportation and industry being the other ones
Mesured in kWh, costs of the energy used or carbon emited.
Carbon Dioxide Emissions
Eletricity also have CO2 emissions, more or less depending on the source of energy in the region
Primary energy sources have the more energy As it is converted for transportation and use as site energy, part of it is lost.
Types of sustainabe buildings
Sustainable Building (environmentally, economically and sociallly)
Zero Energy Building/Net Zero
Green Building (energy use)
Zero Carbon Building/Net Zero
Solar radiation
Spectral Considerations
The sun's radiation is filtered in certains frequency bands due to earth's atmosphere
Special materials can selectively reflect or absorb desired radiation spectral bands
Black body radiation theory: all badies emit radiation acordigly to their temperature.
The sun's radiation can be reach the earth's surface directaly or scatered, from the atmosfere (diffuse)
Sun's radiation is smaller (a little lass than a half) in polar regions than near the equator and certains mid-latitude areas. This is due to the angle the radiation reaches and the thicker layer of atmosphere it has to pass through. Sun llight is still has a impactfull force there, though
Daylighting is a Global Solution: up to 50º latitude daylight can illuminate interior spaces for 80% of core commercial hours
Graphs can showhow much and where sun radiation comes from over the whole year or in each month of the year on average. This is important to know when blocking or leting it in
Sun's path
Local Solar Coordinate System: Solar Altitude and Azimuth
Solar time: local time, measured by sun's cycle on the
Sun Path Diagram
Analemma: graph showing the sun at the same time, everyday over a year. It shows a shape of a 8 due to Earth's axis inclination and its eliptical orbit around the sun
Wind
Wind energy can be caculated to the place where you want to build a wind turbine. It's easier to calculate this in an open, plan site. Wind patterns near buildings, tress atc. are hard to predict.
Wind turbines cause noite and vibration.
At small scales, for buildings, wind turbines are more expensive than photovoltaics
Future Climate
Scientists can calculate how the clllimate will be like in all regions of the world using models and past data. This information can be useful for architects to make buildings that can still use passive cooling methods in the future, for example.
There's a trend for global warming and this will cause decrease in heating and increase in cooling, with energy source changes coming from that
Thermal Comfort
Measurements
Climate data
Main types of Climate data
Direct solar radiation (W/m²)
Diffuse horizontal solar radiation (W/m²)
Wind speed (km/h)
Wind direction (degree)
Optional:
Cloud cover (%)
Preciptation (mm)
Dry bulb temperature (ºC)
Other units: Kalvin (K) and Fahrenheit (ºF)
Relative humidity (%)
Water takes a lot of heat from a surface when evaporating. Dryer air creates more evaporation and thus cooling
Is measured in weather stations and their data can be found online for free. It's important to noteice that the microclimate of a place in the same city can be different
Typical Meteorological Year (TMY)
The data is based on measurements collected over at least 12 years. For each month, the measured monthly data for the year closest to the mean of all 12 years for that month is used, resulting in a collection of monthly measurements that may or may not stem from the same year.
Drawbacks: Based on historical data and do not consider climate change. Do not show extreme climate events.
Other climate data
Wet bulb temperature - Takes the effect of air moisture and evaporation into account
Psychrometric Chart
Chart that plots the relation between dry and wet bulb temperature, relative humidity and quantity of water in the air
Photometric quantities
Descriptions of a space
Illuminance
Overall amount of light that falls on a sensor. Unit is lux. Most used measurement in standards because it's easier to measure and can be shown in 2D maps. But this is not as similar to the human experience as image-based measurements as HDR images.
Luminance
Amount of light percived from each point in an ambient. Unit is lumen or cd per m². Is measured by a special sensor that gives the luminance for each point, but now HDR photos from calibrated cameras can be used to measure the luminance of each point of a picture.
Descriptions of light sources
Luminous flux/power
Amount of light emmited by a light source. Light bulbs come with this information. Measured in candela or, in SI, 1 lumen/starradiant
Luminous intensity
Describes the spectral distribution. More important for designers.
Air conditioning/heating
Loads
Latent loads
Cooling required to remove moisture from the air
Sensible loads
Cooling required to cool the air
Amount of internal energy in the air
Air humidity
More air humidity demands more cooling loads to remove the water from the air.
Enthalpy: energy stored within air
Heating
Heat Recovery Ventilation
Device that makes the heating more efficient by controlling the air exchenges,
Heating drops the relative humidity
Relative humidity may rise to dew point in cold areas, such as windows. This may cause problems to the building
Fresh, drier air needs to be brought into in those places where water may acumulate. A Heat Recovery Ventilation makes this more efficient since it "rescue" back some of the heat that may be lost.
Air moisture
To remove air moisture, you need to cool the air to make it reach the dew point, even if you have to heat it after.
People add moisture to the air naturally, witch helps when the air umidity is low.
Evaporative cooling/Adiabatic cooling
More simple and energy efficient, uses the natural evaporation of water to cool dry air following the enthalpy lines of a psychrometric chart
This can be used in umid weather too if the air is dried first (this can be done by absortion)
Definition of Thermal Comfort
Used to be the lack of disconfort
Now, acording to ASHRAE, thermal comfort is a condition of mind which expresses satisfaction with the thermal environment as assessed by subjective evaluation.
Can be measured bt the 7 degree ASHRAE thermal confort scale
Depends on clothing, activity, individual's biology, personal preference
Metabolic rate depends on activity and is measured in Mets. People radiate energy, heating a room.
Clothing effect on someone's heating is measured with the unit Clo.
Thermal confort index
Uses several aspects to give a number that rates the thermal confort. Over 100 of them have been crated over the years. The most used is Predicted Mean Vote
Confort Range
The thermal confort can change acording to the seasons because humans like some variation, they wear different clothes in differnt seasons etc.
ASHRAE 55 - Confort Range Standard for buildings with heating and cooling
CBE Comfort Tool for Predicted Mean Vote (PMV) and Adaptive Thermal Comfort
https://comfort.cbe.berkeley.edu/
Predicted Mean Vote
For when the building uses air conditioning
Adaptative Temperature
For when the building uses natural ventulation. A more lenient model. Has some criticism.
Spatial Thermal Comfort
We feel an average of air and surfaces temperatures. People don't like too much thermal imbalances in a room, but slightlly cooler cealings for our heads and warmer floors for our feet is acually good
Daylighting
Active solar
Sky Models
There are models that help simulate the sunlight and diffuse skylight. Different models can give better simulations and different uses
Main examples, from oldest and simplest to newest and most complex: Uniform day, Overcast sky, Clear sky, Utah sky, Perez Sky
sky models of the radiance of the celestial hemisphere important to energy analysis, lighting and even spectral effects on human health
Radiation Maps
A radiation map is a false color rendering of an outside object that depicts the solar radiation falling onto individual surfaces of the object visible in the rendering. Can be calculated for a date or the whole the year
Can be calculated with the DIVA plug-in
Useful for solar PV, shading etc.
For Calculating PV Electricity Yield, it's only needed to multiply the size of the panel, its efficiency and the solar radiation to the given point of the geometry
Opposite to passive design which uses only the form of the building, active design uses devices to manage or use the sun's radiation
Photovoltaics
While the prices of the materials have been falling dramastically, the price of instalation haven't changed and is now a big part of instaling PV
PV instalations are growing exponentially, with Europe, Asia/Pacific and North America leading by far
PV panels
PV panels are made of PV modules (or Solar cells) in series
PV modules are made of a doped silicon crystal that creates a currrent with exited electrons when sun shines on it.
Eletric output drops signifcantly when one or several cells are shaded. Blocking the production of a single cell can block the current a whole series of cells
Tilting the panels to the maximum orientation can make each panel more productive, but this tilt can cause self-shading between panels close to each other. Many other factors can influence, like wind loads, aesthetics etc.
To connect the energy produced to the grid, a invertor (AC/DC converter) is needed. This is the more expensive and the least lasting peace of equipment of this kind of instalation
Amorphous solar cells have a more uniform visual but are less efficient
There are big governamental incentives for PV in the US and other regions. THis makes usinng PV very worth it.
To calculate how much energy a PV panel will generate in kWh, multiply the solar radiation that falls on the desired area (kWh/m²) with the panel's efficiency (%), the AC/DC converter efficiency (%) and the area of the panel (m²)
PVs and the Grid
If a big proportion of people started using PVs to generate energy, this would be a chalenge for the grid, since it doesn't provide constant energy, it would require much more flexibility from other power plants because of the huge increase of demand when the sun sets. This is the situation that causes the "Duck Curve" in the energy demand curve in a day.
Increasing the number of PV systems, which are expensive and don't work all the time, in out current grid and energy consuption style would be a waste of money since the energy companies would need to more expensive utilities.
Soon people won't only have to think about building Energy Zero homes but also homes that are good for the Grid. Possible solutions include:
IoT could distribute part of the energy consumption of smart devices to late in the night, for example. This could even be controlled by the utility company
Using home batteries would be a solution for the Duck Curve but would create another big problem for cloudy days with everybody demanding again all at once. These batteries are good for emergency backups in energy insecure areas,
Using Feed In Tariffs instead of Net Metering. Feed-in tariffs incentivize home owners to adjust their load curves to the demands of the grid by either storing surplus energy in a home battery or by using appliances at different times
Solar hot water
An ancient idea
Solar collectors
Solar collector Types
Flat plate collector
Most common
Vacuum tube collector
Heats to boiling temperatures, more used for industrial processes
thermosiphon system
Sizing a solar collector in summer
First of all, "how much hot water do I need?"
Typical hot water use is 40l/person per day (this is variable)
It's needed to know
the temperature of the water provided,
the desired temperature and
the solar radiation in the summer
This can be checked in a radiation map
Light and Human Vision
Human vision
The eye needs time to adapt to a new environment with different light intensity. With big differences, it may take 10 min or more depending on age.
The light is absorbed by 3 different types of cells in the retina:
Rods, responsible nighttime vision (Scotopic) and the periferal vision. Can see dim light but not colors.
Cones, responsible for daytime vision (photophic). they have 3 sub-types to see the primary colors red, blue and green
Ganglion cells (recently discovered and now yet well understood) have peak sensibility at the blue color and can supress melatonin production
seasonal affective disorder is condition caused by lack of daylight in northern regions and can be treated with strong artificial light
Cones and Rods working together give the Mesophic vision, between the photophic and scotophic vision.
The human eye can see in a huge range of light intensity (12 orders of magnitude, from 10^-6 to 10^6 cd/m²), from starlight to sunlight, but only in a fraction of this range at a time (3 orders of magnitude in cd/m²).
Photometry - Luminous Flux
The luminous response curve of the human eye is stronger around the green spectrum in daytime vision and stronger around blue light in nighttime vision.
Daylight is the visible electromagnetic spectrum, between 380 and 780nm
Spectral distribution of light sources
Affects color rendering
Related to luminous flux
See Photometric quantities in 'Measurements'
People have different preferences in amount of light needed, so giving the power of choice to the user with a dimmer is ideal.
Daylighting Design Principles
Daylighting is the act of lighting the interior or exterior of a building with natural light.
Daylighting Framework
3 main aspects of good daylighting
Daylight availability: There is enough daylight in a space throughout the year
Energy: The daylighting concepts help to reduce building energy use
Visual comfort: Occupants find it neither too dark nor too bright
Beauty and architectural expression
Ocupant control
Daylight Dashboard
It's a simulation that gives you a snapshot of the projected performance of your building design in terms of amount of light, shading devices, glare, solar heating etc.
A much simpler and hands-on approach is using scale models in the sun to see how sunlight will interact with it.
Daylight Availability
Daylight autonomy
Simulations may draw lines around places that have daylight autonomy but that doesn't mean those are 'boundaries' and the rest doesn't have daylight.
Daylight autonomy corresponds to the percentage of the occupied time in the year when a target illuminance of 300 lux is provided by daylight alone within a building
Different locations in North America doesn't change the Illuminance map so much in computer simulations, so rules of thumb apply
Façades oriented to the equator get more sunlight
What Surfaces Matter?
Ceiling
Glass
Different types of glassing have different light transmittances. A good target is 60-80%
Outside ground
The sunlight bounces from the ground to the ceiling and then to the deep parts of the room. Light colors are important
Reflectance
There are mirror-like and diffuse reflections.
The reflectance of a diffuse reflector material can be obtained by measuring the Illuminance falling on the surface and the the luminance of a point in the surface. Then, caculate the rest (expensive method).
Reflectance of materials can be compared in CIBSE reflectance charts which comes with examples (cheap and works better)
Daylight Area Exercise
The goal is to understand how building occupant evaluations of the daylight within spaces compares to daylight availability simulations
Users of built spaces are asked to draw the daylit areas and then this is compared to a simulation. The average of the responses trend to agree with the simulation in the most part but in extreme cases, not so much.
Rules of Thumb
Rules of Thumb are useful principles of wide application that are not intended to be accurate or reliable in every situation. In this case, they can be used for the daylight potential for the massing of a building
The #1 geometric propertythat determines how deep the daylight enters the space is the height of the window. (following rules aplies to the US)
With venetian blinds, the daylit area distance from the window usually is 1.5 to 2 times the window-head-height (from floor to window head)
Without shading devices, this number increases up to 2.5
External obstruction: the sky angle (vertical angle from zenith to the top of the building in front) times the window-to-wall ratio have to be above 2000. To calculate the needed window-to-wall ratio: WWR>2000/angleΘ. Cutoff level for WWR is about 80% (fully glazed façade)
For daylighting, the height of a atrium have to be lower than 2.5 times the width of the atrium
Skylights and Urban Massing
In the US, only 2-3% of a ceiling is needed for skylights to daylight a whole building
Since most skylights have some thickness due to the plenum of the building, a slanted ceiling can improve the daylighting capacity 8-9 times. Decreasing the thickness of the roff is even better.
Daylight simulations can be made for the massing of whole cities. This can be used to test different urbanistic guidelines and help urban planing
Daylighting Simulations and Availability Metrics
Daylight Simulations
Simillar to Architectural renderings, they use surface-based models to render lighting. The materials need to be separeted in layers and have correct properties. Pay attention to trees, nearby buildings, thickness of walls and llight leaks
Can be used for:
Demonstrate code compliance and reduce risks (e. g. for certificates)
Compare and analyse desgin
Firms that have in-house modelers usually have simulations impacting the design more.
There's a consensus that designers should do the simulations themselves too so they are more effective.
Computer renderings that can be done for both Luminance or Illuminance.
Daylight Factor Calculation Methods
Global Illumination Methods
1940s Daylight Factor Protractors + Original Split Flux Method
1980s Radiosity (has some advantages over ray tracing)
1990s Split Fllux Method in Ecotec
1920s Waldram Diagrams
Rendering tools nowadays use Radiosity, Ray Tracing or a combination of both methods
Radiance (Raytracing)
Simulation parameters
Light bounces
'Magic lies on the simulation parameters'
Ambient division
Simulate light rays coming from the 'camera' at a point, passing though a grid (pixels) and hiting visiblle geometries with realistic materials.
Can simulate reflective and refractory materials
If you simulate a sidelit space very carefully, how accurate can you expect a daylight simulation using Radiance to be? For a variety of different sky conditions, I will end up with a mean relative error of around 20% (a very good result)
Which global illumination method is most accurate when it comes to calculating the daylight factor? This depends on the application. For “simple” narrow façades, all methods may lead to comparable results. However, the methods diverge when daylight enters a building via multiple reflections.
Common rendering mistakes
Using complex 3D geometries for trees - only a plane turned to the building is needed
Not considering windows' frames, wall thickness, ceiling, the correctly configured materials
Simulations always tend to be better than reality because we forget trees, nearby buildings, surround ground, etc
These simulations can take hours to be done, but advances in graphic cards are making this time shorter, even to the point of making real-time walk-thoughs, which help desginers to make even more evaluations in a state of flow
Daylight Availability Metrics
What are key limitations of the daylight factor compared to a climate based metric?
The daylight factor yields the same result for any building orientation.
The daylight factor is independent of the local climate.
Visual Comfort
Types of glare
Disability Glare
Glare that precudes a person from seeing a object. Ex.: when a lifeguard can't see all swimmers in a pool.
Three leading causes of disability glare in the built environment:
Disability glare can be caused by a convex façade with a specular reflective glazing
Disability glare can be caused by a flat surface with a strong forward scatter optical refelction
Disability glare can occur when wall is painted in a highly reflective, matte white
Disconfort glare
An occupant can still see all objects of interest within a scene but the overall brightness or luminance contrast within a scene cause strain of the eye which – over times - might lead to discomfort, premature tiring of the eye and other effects.
People can easily adapt in some situations just by moving or turning a little and this flexibility should be given in architecture. It's important to notice the balance between confort and visual interest.
The two terms that daylight glare probability relies on to predict the likeliness of glare at a given moment in time and in a particular view direction are scene brightness and contrast
Veiling Reflections
The latter is really a subset of the former two and corresponds to times when reflectances of specular surfaces act as glare sources.
Definition: the absence of visual disconfort (no occupants complaints)
A more nuanced definition: the balance between visual liabilities (glare, veiling reflectances, lack of privacy) and visual assets (view, acess to daylighting, visual connection to the outside)
Long-term Visual Comfort
For screens, people need a contrast ratio over 3 or 4.
People can accept an certain amount of glare if it's just for very few moments of the year/day. This varies acording to the building.
Ex.: At MIT, the students in the Gund Hall study potentially experience disturbing glare while still finding their workplace visually comfortable 4% of the time.
Visual interest
Connectivity (how much of the space I can see from a POV). Less conectivity makes more private. More connectivity makes more social and on control
View and daylight area: only the middle part of the façade gives views. The top is mostly important for daylighting. So the top and the bottom of a window's shading system could be controlled independently, with middle being more closed to prevent glare and give privacy while to top gives light. The bottom of the façade gives little views and daylight so it can be a wall to avoid solar gains.
View
A view is a universally recognized asset in architecture and real estate.
Benefits of a window include occupants’ ability to focus on a faraway point to adirect link to the outside world.
It seems surprising that there are no well established metrics to evaluate a view.
A view requires:
direct lines of sight between an inside observer and select outside objects
content
since views work two ways, a view may become a privacy concern
Real State developer are the ones interested the most in views since it adds lots of value to buildings.
Having views for multiple directions or to objects of interest is even better.
Research on Urban Views
Views can be computaded - simulations can predict the quantity or quality of views in a project. Two important aspects are sky exposre and visibility of objects of interest
Occupant Behavior
Manual Lighting Control
you have to at least make sure that the lighting, the systems all over your building are turned off when nobody's there.
the moment that matter is when you enter the space first, when you are close to the light switch.
when it's 300 lux, which is our daylighting target level, the likelihood that somebody switches on the light is 10--20%.
The preference for the use of daylight (active user) vs artifical lighting (passive user) depends on the user
Occupants typically switch off the light when they leave. Swinching on or off the light when they are in the space is more unpredictable.
Shading Control
The two main triggers for office workers for closing a dynamic shading system such as blinds
Glare
Direct sunlight right near their work place
shading devices outside the glazing heats the building less
Light Fixtures
Light reflectors are used to manipulate the light distribution emitted by a light source. reflectors of different shapes gives different distributions: Ex.: Parabolic reflactors craetes parallel light rays.
Commercial buildings tends to spend more energy on lighting. Commercial buildings need to follow ASHRAE 90.1 in the US -- the most important lighting standard
Electric lighting
Light sources
Two key characteristics
Correlated color temperature
Color rendering index
Hability to mimic daylight. Important for accurate colors but not always the best metric.
Types
Incandescants
Standard incandescant lamps
A heater that also emmits some light
Halogen lamps
Good for control the light as it can be similar to a point source
Discharge
Fluorescent lamps
Complicaded.
LED
Last much more and spend much less energy. Poor color rendering.
Lighting Design
Types of design variables evaluated by simulating the electric lighting in a space using IES files:
The required distance between lighting fixtures to get an even illuminance distribution at a desired target level
The required lighting power density
The balance between direct and indirect lighting
Choosing fixtures nowadays is easy due to companies giving lots of info and possibility to make comparisons of their models.
Lighting Controls
It's fundamental to turn off the lights when possible to save energy. Designing for daylight and a good electric system is not enough.
Overview of Traditional Lighting Controls
Manual, automated, and automated with manual override
Bi-level switching
Manual dimming
Photocell–controlled on/off
Photocell–controlled dimming
Façade systems.
fewer sensors
less dependent on interior changes
works well for top lighting or in the absence of a shading device
good solution for shared spaces (atria, retail, open plan)
Ceiling systems.
more sensors but more individualized
considers blind setting
suitable for private offices
requires careful commissioning
Occupancy sensors
There are the cheap one that use infrared and are usually next to the door. Not very sensitive but they don't really have to be to check the door.
The more expensive ones can use ultrasounds too. They should scan the whole room.
Can increase the energy use by turning the lights on too much if not in vacancy mode.
Modern Smartphone-Based Lighting
Main task: to only provide as much lighting as required when people are in the space.
Thermal loads
Thermal Mass and Heat Flow
Thermal Mass
Heat
Internal energy is a formofenergy that is stored in a material as molecular motion (sensible energy) or that is associated with the phase of thematerial (latentenergy).
Sensible energy is measured in temperature (concept of absolute zero, degree Celsius, degree Kelvin, degree Fahrenheit).
Latent energy is the amount of heat energy released or absorbed by a substance during a change of phase.
Heat (Q) = TM x (T before - T after)
Heat required to change the temperature of an object. A negative energy value indicates that energy is absorbed by the object.
Thermal Material Properties
Density
Thermal conductivity
Specific heat
Volumetric Heat Capacity
We tend to rely more on Volumetric Heat Capacity than Specific Heat because we need to consider the volumetric quantities in a building.
Even though air have a high Specific Heat like water, it have a very small VHC, unlike water. Therefore, the same quantity of air stores much less heat than water.
In buildings, we usually use air to heat and cool buildings, but considering its VHC, this material is not efficient to transport these loads, unlike water. Air is used because it's more pratical, even though it's not so thermodynamically smart.
Thermal Mass (TM) = Volumetric Heat Capacity (VHC) * Volume
Thermal Mass in Buildings
thermal mass is beneficial to maintaining the indoor temperature of a building within the comfort range when the outdoor temperature fluctuates above and below the thermal comfort range during the course of a typical day
Thermal mass "smooths" the variations of outside temperature. it also creates an effect of "time lag" between the variation of the temperature outside and inside. The grater the thermal mass, the bigger the effects.
High Thermal Mass versus Light Weight Construction
Fever curve graph
Fever curves are frequently used to test the ability of different design to keep a space within a given comfort range.
Fever curve is a graphical method to analyze temperature distributions over the course of a year. The curve shows the cumulative number of all (occupied) hours in a year during which a temperature is above a given temperature.
In an intermittently used space, low thermal mass is better because the space can be left unconditioned when unoccupied. It then takes less time and energy bring it back to a comfortable temperature range when the construction is light-weight
Heat Flow
In order to understand the thermal behavior of a building, it is useful to think of the building as a system with a boundary, with the boundary consisting of the building envelope (basement, external walls and roof). One can predict how a building will behave over time by recalling the first law of thermodynamics, i.e. any excess energy crossing the buildingenvelope is going to be stored in the building’s thermal mass. If incoming and outgoing energy flows balance each other, then the system is in equilibrium and no energy is stored. Equation: E incoming = E outgoing + E stored in thermal mass
Heat always flows from the hottest to the coolest. This is a dynamic process since the outdoors conditions are always changing.
Forms of heat flow:
Conduction, for materials touching
To avoid conduction, we use insulating materials.
Air is a good insulator but the convection increase the heat flow.
Conductance. Property that describes how well a material conducts heat.
C (conductance) = κ (conductivity)/material thickness
Measured in W/m2 K or BTU/h ft2 ºF
Resistance, inverse of conductance: R = 1/C
Total resistance in a material of multiple layers is their sum: R = R1 +R2 + ...Rn
It's more useful for calculations and used in building codes, called as 'R' value in American building codes, which require an certain R value. In these codes, convection of the air layers between an reference point inside and outside the building (these points do not touch the wall) is taken into account.
Convection, for fluids
Radiation, can happen at a distance and without a medium.
Insulation Materials and Window Technologies
Building Envelope Calculations
Windows are the part of the envelope of a building that have the least resistance -- more windows, more conductance.
An envelope with higher resistance will follow the outside temperature more slowly
Phase Change Material (PCM) is an aditive that increases the TM of paints, gypsum boards etc.
Equation to calculate the heat loss rate of a building envelope (measured in W):
Q’ = ΣUA * (Tinside – Toutside)
U value is the conductance. ΣUA (heat loss coefficient) is the sum of all conductances times the area of each part of the envelope.
Building codes
They tells how much insulation is needed for each climate. In the US, it's the ASHRAE 90.1 but each state and sometimes counties will have modified codes. They give the R value in imperial units in the US (1 m2·K/W = 5.67446 ft2·°F·h/BTU)
Insulating Materials
Expanded polystyrene (EPS)
Easy to work with.
Glass fiber
unconfortable to work with due to tiny pieces that can get in your eyes.
Mineral fiber/wool
the best to work with since it's squishy like a sponge, so can be cut a little bigger and easily fit into spaces leaving no gaps.
Cellulose
Mold and fire resistant paper. Blown into cavities. Not good with umidity.
Straw bale
Natural, renweable material that's cheap but not as effective as the others. May atract critters
Vacuum insulation panel (VIP)
Incredible performance, multiple times better than the others, expensive, can't be perfurated.
Window Properties
Visual light transmittance
It's the percentage of visible light that can pass through a glazing normally. Desired to be as high as possible for daylighting.
Solar heat gain coefficient
Consider the whole solar spectrum and the glazing's radiation when it heats up. It's a percentage too.
Window Study
Types of glazings
Sgl_Clr_6 Single pane glazing, 6 mm clear glass (R~1, illegal in the US, τvis=88.4% SHGC =81.8%)
Dbl_Clr_6_6_Air Double glazing: 6 mm clear glass, 6 mm air gap, 6 mm clear glass (R~2, τvis=78.6% SHGC =70.2%)
Dbl_Clr_6_13_Arg Double glazing: 6 mm clear glass, 13 mm argon gap, 6 mm clear glass (R2.2, τvis=78.6% SHGC =70.5%)
Dbl_Clr_6_1_Vacuum Double glazing: 6 mm clear glass, 1 mm vacuum, 6 mm clear glass (R2.5, τvis=78.6% SHGC =70.6%)
Dbl_LoE3_high_solar_gains_Clr_6_12_Arg Double glazing: 6 mm clear glass Low –ε coating high solar gains on 3rd surface, 13 mm argon gap, 6 mm clear glass (R4, τvis=76.2% SHGC =62.9%)
Dbl_LoE2_all_climates_Clr_6_12_Arg Double glazing: 6 mm clear glass Low –ε coating all climates, 13 mm argon gap, 6 mm clear glass (R4.3 τvis=62.8% SHGC =27.1%)
Coatings improve the performance of glazings.
They can be selective to the spectrum of infrared they reflect.
High e-coating low solar gain reflects all infrared, good for hot climates. Low e-coating high solar gain only reflects the far infrared of objects (typically the spectrum that comes from inside) and lets the near infrared from the sun.
The coating heats the glazing it's on. Choose depending if you want heat inside.
Insulation in windows is relatively more expensive than in walls. Walls should be a priority.
20% of a window are frames
Skylights and Passive Solar Heating Potential
Skylights receive a lot of solar radiation and can be used for passive heating.
They may loose heat if there's no coating due to hot air rising to the roof and radiating energy there.
Only a little of skylights are enough for daylighting.
Types
Conventional Skylight R-2 U=2.8 W/m2 K
Insulating Glass Skylight R-10 U=0.5 W/m2 K τvis = 62% SHGC= 0.25
Nanogel filled R-20 U=0.28 W/m2 K (aerogel glazing)
Summary: you want low U value because you want to separate the inside from the outside. That's why you have a building envelope. You want, typically, high visual light transmitters. And then the solar heat gain coefficient, the warmer your climate is the lower you want it to be. Cold climate you want it high. And for the in-between climate, you do an annual performance simulation.
Radiation maps calculated for heating months can be used for building and urban planning to check when windows are beneficial or a liability for heating. Windows that get a lot of radiaiton are beneficial, windows without it make the building loose heat.
the solar radiation times the solar heat
gain coefficient times the fudge factor (1.6 W/Km²) needs to be bigger than the heating degree hour times the U value for a window to be useful for passive heating.
Shading and Integraded Facade Design
Static Shading
Why Shading?
Avoidance of visual discomfort (glare).
Avoidance of thermal discomfort (overheating).
Avoidance of cooling loads (energy).
Why not Shading?
Solar gains needed to reduce heating loads.
Maintain a view to the outside.
Basic Guidelines For Designing Static Shading Systems
Use horizontal shading systems such as blinds and overhangs for equator-facing windows. Horizontal elements effectively block vertical surfaces when the sun is high in the sky.
For east- and west-facing windows vertical shading elements are preferable because they can block low solar altitudes which may trigger glare and overheating during the summer.
Façades facing away from the equator do generally not require static shading since direct sunlight is rarely incident on these façades. (obs. in 2021: in the tropical region, façades facing away from the equator can also have direct sunlight).
Horizontal and vertical shading systems can be combined.
Should be designed based on solar and climate studies. Sun radiation should be blocked or not when the building need solar gains or not (among other things).
Radiation maps are useful to see which areas should be shaded and to test shading systems on the trial and error method.
Geometric solutions for the shading of a window can be made from 2D or 3D methods that, based on when the sunlight needs to start being blocked, discovers the size of the shading system that is needed. Actually it's the angle with the sun that's important since making multiple shadings of smaller size works the same.
Some methods will not take into account the losses in daylighting and heating that completely blocking direct sunlight causes. There's a component on DIVA called Shaderade that try to find a balance between shading and heating in the winter.
Can be a big part of the a architectural comcept in contemporary architecture.
Static vs. Dynamic Shading
Building does not require/allow for user intervention.
Architectural perception of exterior movable shading devices is that they look 'messy' (Lam), are complicated to maintain, subject to freezing rain (climate dependant).
Movable shading devices (venetian blinds) offer a dynamic response to a dynamic signal.
Trees and other vegetation can function as a compromise.
Dynamic shading devices are 'risky' because occupant responses are difficult to predict.
Shady: a shading device in the windows that follows you.
They performance simulations for shadinds must consider their structure and thickness that will be used in the construction, not just the shapes used in the conception.
Integrated Façade Design
When internal, shading systems heat up with sun's radiation and radiate this to the room in infrared. Windows with low e-coating trap this radiation inside.
External dynamic shading systems may break more due to the elements.
Simulations in DIVA can show the best trade-off between shading, heating and daylighting
Innovative Façade Components
Aerogel glazings are expensive but offer diffuse daylight and thermal properties of a wall.
Split blinds can have the lower and the upper part adjusted independently can offer slightly better daylighting.
Electrochromics is a switchable glazing system that uses a electric current to change the optical transmitance of a window on demand. They can reduce excess light but can't fully block glare. They keep the view to the outside.
Thermotropic glazings are polymer blends that turn opaque and slightly translucent when switched on. Only needs electric current during the transition, which takes minutes.
Ventilation
Ventilation introduction
Ventilation is the use of air to provide acceptable indoor air quality.
Forced ventilation is the intentional movement of air in and out of a building using fans, intakes and exhausts vents.
Natural ventilation is the flow of air through planed openings in the building envelope such as windows, doors, grilles etc.
Infiltration or exfiltration is the flow of air through imperfections of the building envelope. They may be a important part of ventilation.
It's needed 10 liters of hygienic fresh air per second, per person, for breathing and indoor air quality should be provided to the inside of a building
This can be converted into Air Exchange Per Hour, based on the size of the building and how many people are there. This shows how much of the air volume in a building needs to be replaced every hour.
Infiltration
Blower Door Tests
A fan creates a negative pressure in a building with closed windows etc., forcing air in though the leaky points of the envelope. Those points can be investigated during by feeling or measuring air coming in with a incense. Measuring how fast the preassure of the building gets reduce express how much infiltration there is. Results are expressed in m3 /m2h @ 50 Pa of negative presssure.
There is a difference between ACH50 and ACHnat. You want to reach an ACH50 < 3. An ACH50 < 1.5 means that your house requires mechanical ventilation.
Energy efficient houses have been found to have an average ACHnat of 0.5 h-1 (range 0.02 h-1 to 1.63 h-1), compared to 0.9 h-1 for ‘normal new construction houses’.
Ventilation Losses
Energy loads on a building due to infiltration and ventilation are dependent on the amount of air changes per hour:
Qinfiltration= (ACH x volume x c x ρ) x (Tinside-Toutside)
Where: ρ = Density of Air 1.2 kg/m3
c = Specific Heat Capacity of Air (20°C) ~ 1000 J/kg K
How many times the volume of air in a building is changed per hour shows how much air accually needs to be conditionated.
Residential Weatherization Techniques (avoid infiltration)
There are several products in the market like pads or wraps that help seal windows, doors, walls etc.
Natural ventilation
It's free, it avoids cooling loads, it's atractive.
It's not always possible to have only natural ventilation in some non-residential buildings, but a hybrid system is always possible.
Even in colder climates, it's smart to allow natural ventilation due to climate change.
Climate data is very important to know when natural ventulation is good. When it's too hot outside, natural ventilation should be avoided too.
The amount of natural ventilation needed for cooling depends on the cooling load needed and the outside temperature (directly proportional). This amount comes from a graph from the book Natural Ventilation in Non-Domestic Buildings, by CIBSE
Natural Ventilation Potential
Ocupants need to be warned when it's apropriate to open the windows. An example is the Syracuse Center for Excellenceby Toshiko Mori, which uses lights to tell that.
Not only temperature influences when it's good for natural ventilation, but noise and pollution too.
See the book Natural Ventilation in Non-Domestic Buildings by CIBSE
Air flow
Buoyancy
Density difference between warm and cold air induces air flow.
This can be useful for buildings in what's called Stack Effect or Chimney Effect.
Strategies:
Use a solar chiminey. They maximize heat gains in unoccupied spaces in elevated heights. It heats air which expands and exausts, creating a negative pressure that drives in colder air bellow
Similar: Evaporative cooling tower.
Maximize inlet and exaust height difference and size
Usually expressed through a volume flow
rate "q". Units: cubic feet per minute (cfm) or l/s
Ventilation rate is also expressed per person or per unit floor area
q = area * velocity
Air flow happens when there's air pressure difference.
Driving Forces for Airflow in Buildings
Pressure difference (sqr(2ΔP/ρ)) can happen due to wind or bouoyancy
For wind, it depends on wind speed and two coeficients for the window
For buoyancy, it depends on indoors temperature, temperature diffference with the outside and the height difference between two windows
Air flow, q , and air exchange rates, ACH, are closely related
Calculation Procedures
Envelope flow models (semi-empirical models)
Computational fluid dynamics (CFD)
Combined thermal and ventilation models
Physical scale models
Occupant behavior
Pleasant sounds and smels from nature induce people to open the windows
People needs to be reminded to when to open or close windows. An example is a building that shuts down the heating when the window is open. When it's cold again, people will need to close it.
Wind-induced Air Exchange
The bigger the windows, the better, but they need to be opened in the right moments.
Wind driven air flow in a single sided single vent:
q = CAU (C=pressure coeficient ~0.025, U=wind speed, A=windows area)
Cross-ventilation.
Narrow buildings are better for
The coming wind push against one side of the building (positive pressure) and leave a negative pressure on the roof and the oposite side. Air wil try to follow the path from positive pressure to negative pressure.
Wind vs chiminey effect
Wind ventilation is much more effective, but is more variable and therefore, less reliable, specially in certain areas.
Therefore, it's useful to plan for both.
Consider fan assisted natural ventilation. it has low energy consumption and helps when wind or buoyancy is not enough.
For natual ventilation, the bigger the window, the better. For buoyancy, vertical size matters too.
Barriers to natural ventilation
During design
Building and fire regulations (biggest one)
Need for acoustic protection
Designing a naturally ventilated building requires more work but can
reduce mechanical system (design fee on a fixed percentage of system's cost)
Increased risk for design team (occupant behavior)
Difficult to predict pattern of use
Devices for shading, privacy & daylighting may hamper the free flow of air
Problems with automatic controls in openings
During operation
Occupants not understanding the system
Safety concerns
Noise from outdoors
Dust and air pollution
Solar shading covering the openings
Internal Gains and Load Calculations
Internal Heat Gains are divided in three groups:
Heat from occupants
Heat from electrical equipmentand appliances
Heat from electric lighting
It's considered a different group from equipment due to lighting being part of architectural design and thus more under control of the designer, unlike equipment.
Occupant Loads
Turning things off when noone is in the building is the biggest savings one can accomplish in certain buildings
People genarate heat and moisture to the building. It depends on age, gender, activity etc. but the heat is 100W on average.
Maximum occupancy heat gains = activity-related heat gain * no. of people / conditionated floor area
Schedules of occupancy are important for simulation programs to calculate the occupant loads throughout the day.
Equipment and Lighting Loads
Heat gain due to a variety of equipment, including computers, coffee machines, hot water pipes etc.
Sun Wind and Light (Chapter 4) provides lower and upper margins for different buildingtypes:
Offices : 8 to 17 W/m2 (Studioload typicallyaround 26 W/m2)
Education: 14 to 23 W/m2
Residential: 2to 6 W/m2
Schedules of occupancy are important for simulation programs to calculate the occupant loads throughout the day.
It's more difficult to predict how much heat the equipment produces.
Thermostat Settings
Different Thermostat Models
Manual
Programmable
Self-learning/wireless
Common Misconceptions about Thermostats
Thermostat is an on/off switch
Thermostat is a dimmer switch
Thermostat is an accelerator
Turning down the thermostat has little or no effect on energy consumption
When people don't have good insulation and a tight envelope, they tend to use more heating to compensate.
Schedules are important to know when to heat a building. IoT can help with that (but sometimes tech can go wrong)
What does a thermostat setback do?
It relaxes the target temperature at a thermostat to a lower temperature for heating and a higher temperature for cooling
Load Calculations
In a cooling dominated climate, the equipment loads are very important to be decreased
Definition of the balance point temperature: The balance point temperature corresponds to the temperature at which a building is in thermal equilibrium with the outside as conduction and infiltration losses ideally cancel out solar and internal gains
Deep buildings always need some cooling, even in winter, due to the amount of internal heat sources (usually done by just blowing fresh air in.
An architect and a HVAC engineer must work toghether to reduce the loads in a building. It isn't the architect's job to specify how, but he still needs to talk with the engineer anyways because sometimes architectural solutions are needed. Ex.: if a cooling load needed to too small to be worth it to buy a air conditioner, an architectural solution will do the trick.
Load definition
The ideal load is the amount of heat that has to be added or subtracted from a space for it to maintainthe zoneair temperature at a certain level.
Load is measured inkWh or BTU.
Normalizingtheload to the conditionedarea helps to comparedifferent spaces. (EUI equivalent.)
The load of a space does not correspond to its energy use which requires further conversion dependingon the HVAC equipment used
Manual Load Calculations
Solve the heat balance equation for each hour
independently (steady state) and can be implemented, for example in Excel.
Numerical Load Calculations
also take transient thermal effect from thermal mass into account. Examplesimulation programsare EnergyPlus, TRNSYS, eQuest/DOE2 and ESP-r. In 4.401/4.464 weare usingEnergyPlus through DIVA4/Archsim.
Building Energy Model
Is a thermal simulation software that also rates the performance of the building
Has two purposes:
Load calculations
Engineers care about this, they just want to make a system that can cool or heat the building enough
Energy Analysis
Designers care about this when they care about sustainability and costs
What does one need for a Building Performance Simulation (BPS)?
building model
simulation program (GUI & engine)
suitable metric
Energy Plus
Is a American Energy Model of great use.
Building Energy Models for design purposes are perfect for checking relatively what's going on, not so much for exact numbers.
Ocupancy, weather files, infiltration and plug-loads tend to not be the same number as in reality and are hard to predict. They make the buildings' calculatioons go somewhat off but the models are still useful to analyse the building itself.
Should Architects use this?
Simulations can give more varieted designs than rules of thumb.
AIA says it can help the architect know if the design is efective and should focus on the orders of magnitude, not small numbers.
Good to understand better what's going on with the engineer's work and graphs
HVAC for Small Buildings
General Considerations
The main purpose of an integrated project delivery approach to building design is to foster collaboration and joined ownership among different members of the design team (so both designers and engineers have responsability over the HVAC systems and thermal confort of the building once they collaborate in this, instead of it only being the engineers' responsability).
So far we have concentrated on quantifying and optimizing energy loads in buildings for heating, lighting, cooling, and internal gains using basic building design and passive systems concepts. Now we are looking at the mechanical heating & cooling systems that are required to meet these loads.
Heating
Heating systems
Source Energy
Solar
Wood
Oil
Gas
Biomass
Electricity
Heating System
Furnace
Solar collector
Baseboard heater
Heat pump
Distribution System
Air
Advantages
Ventilation, cooling and humidity control
Disadvantages
Space requirements
Water
Advantages
Limited space requirements
Radiant heating and cooling
Disadvantage
No ventilation
No humidity control
Electricity
Advantages
Space requirements
Flexibility; easy to control, cheap to install
Disadvantage
No ventilation
No humidity control
High operation costs
Examples of Heating Systems
Hydronic heating distribution systems
To consider: pipe expansion, air vents and water drains, pipe insulation
Perimeter Loop
One pipe
Two pipe reverse return
Radiant Panels
A radiant floor has a larger heat exchange surface than a conventional radiator and may hence operate at a lower temperature.
Furnaces
Condensing Furnace
As opposed to a regular furnace, a high-efficiency or condensing furnace extracts so much heat from the exhaust gases that water vapor in the exhaust condenses. Such furnaces mustbe designed toavoid the corrosion that this highly acidic condensate might cause. No chimney is required.
Fuel
Natural gas
Allow automation of the process. No poor air quality. Contributes to global warming.
Wood
Causes poor air quality. Cheap. More work intensive.
Wood pellets
Burns better than wood and comes from a waste product (sawdust) which makes it almost carbon neutral. Easier to work with than wood.
Heating have a long history from the simple open fire to the fireplace and to the regular furnace. Wood is burned to create heat, but the newer systems try to have better efficiency and air quality.
Air conditioning
Invented in early XX century for food refrigeration and used as a luxury in buildings until mid century.
Cooling systems
Compressive refrigeration (more physical process)
Absortion refrigeration (more chemical process)
Their work is based on the Heat Pump
Considerations
Heat pumps can be used for both heating and cooling.
They can make 2 in 1 air conditioning devices that are easy to install but the heating is not as efficient as other systems (or at least used to be since now they are being sold in places with much colder winters)
Historically, utilities tend to promote heat pumpssincethey tend to rununder capacity inthe winter.
Nowadays heat pumps are promoted as the goal is to reach an all electric energy supply system. As the electric grid is getting decarbonized, heat pumpsare againconsidered to be a viable, energy-saving technology.
Heat pumps work well withradiantheating systemsas they providelow temperature energy.
The heat being pumped into the ground during summer will heat it up and make the system less effective if the heap is not recovered during winter.
The deeper you go into the soil, the less the temerature fluctuates over the year. At 5m, it's almost the same all the time.
Heat pumps works by moving a refrigerant through the refrigeration cycles, cooling in the expansion valve and heating up in the compressor. This makes the heat from a heat source to a heat sink
Mini split systems and ground source heat pumps work on the same physical principle, but the latter (ground source heat pumps) uses the ground as a heat sink or reservoir
Examples of systems that use the ground for heat pumps:
Ground Source Heat Pump
Vertical (more expensive, efficient, uses less land
Horizontal (less efficent and expensive, uses more land)
Groundwater (less expensive of all, uses aquifer, which may not be alowed due to environmental issues)
Ground Source Heat Exchanger (used for cooling incoming air)
The term "Geothermal" is often used to refer to ground source heat pumps but an actual Geothermal system used hot temperatures from kilometers deep into earth's crost.
HVAC for Large Buildings
Duct Sizing
Depends on two main components: (the bigger one is used)
Number of people (freash air supply)
Maximum heating or cooling load
The standard air speed of an air duct is 1.5m/s.
Duct size is the needed air in m³/s divided by the air speed in m/s. The result is the area of the cross section of the duct.
Then, we need an equally sized return air duct.
Positioning Ducts
Laying the suply and return ducts in a building is a puzzle. They occupay a lot of space and that's why plenums are so big. Not thinking about the ductwork early on the project can make it more difficult later.
Ducts outside needs to be very well insulated.
Breaking up the HVAC and duct sistems in smaller units makes the project more complicated and the system less efficient, but make may make the ducts smaller.
Air terminal boxes (ATUs) receive air from an AHU and control airflow and sometimes temperature of the supply air into a specific room or zone to maintain the desired space temperature.
Laboratory and Fume Exhaust Fans: they are big machinery that sucks the air from labs and throw it as high as it can do so people in the neighborhood don't breath it.
Peak loads can be calculated in simulations
HVAC Systems
Heating/cooling takes a lot of space.
Devices
Absorption Refrigeration Cycle
Thermallydrivencoolingsystem whereheat is usedto regenerate the salt solution.
Less efficient than compressive refrigeration but can already work at low thermal heat (60o C), i.e. high grade energy (electricity)usedto runa compressor is replaced with low gradeenergy (heat).
The heat to concentrate the salt solution can come from natural gas (direct fired) or waste heat (indirect fired) or even the sun.
Centrifugal Chiller
Cooling Tower
In larger buildings a secondary loop consisting of water is used to cool the evaporator coil. The water is transported from the coolingunit to the roof of the building and thencooled by evaporation.
Condenser Water Systems
Boilers and hot water systems
Used to generate hot water or steam though pipes for various devices for heating, domestic hot water or dehumidification.
Components of a HVAC System
Zone requirement (heating/cooling needed)
Air handling (distribution)
Cooling/heating
Heat rejection/absortion
Architectural solutions for smaller plenums/ducts
Underfloor plenums (they make the ceiling disponible for thermal mass, lighting systems, aesthetics etc.
These solutions make the needed ducts to be only the one for fresh air, by conditionating the air that is already in the building:
4-Pipe Fan Coil Unit
Radiant Ceiling Panels
Chilled beans
Other technologies
District Cooling and Heating
Heating and cooling ffor several buildings is centrated in one building. More efficient due to the bigger scale. Popular in campuses.
Combined Heat and Power
Again, it can be more efficient to produce heat, chilled or cooled water and energy in the same building.
