Insulation and Energy Losses

An estimated 60 million U.S. homes have inadequate insulation which wastes energy and money, and emits enormous amounts of CO2 (Carbon Dioxide or greenhouse gas) into the atmosphere. Better home insulation greatly reduces your energy costs. Insulation reduces the movement and transfer of heat and cold, which helps you to keep your home warm in the winter and cool in the summer. Insulation performance is measured by an R-value, which summarily represents its ability to resist heat or cold transfer. The higher the R value the better the insulation. Insulation quality is affected by other factors not represented by the R-value. While R-value rates the effects of the convective loops inside the insulation, it does not quantify the air leakage through a wall assembly with the insulation installed. Air leakage is inversely proportional to insulation density, the presence or absence of air barriers in the wall assembly, wind speed, and the stack effect. Because of these additional factors, a leaky wall insulated with fiberglass bats will perform worse than the same wall insulated with spray foam that has the same R-value as the bats. The performance differences are due to spray foam’s ability to reduce or eliminate the air leakage.


The highest R-value provides the best insulation. Material’s R-value enumerates its resistance to all three heat-flow mechanisms – conduction, radiation, and convection – and therefore it is a useful method to compare insulation products. Different R-values are recommended for walls, attics, basements and crawlspaces. For example the recommended attic value for our area is R30. Here are a few facts about insulation R-values:

Although one type of insulation maybe thicker or thinner than another, but if the R-value is the same both materials will insulate equally

  • Although one type of insulation maybe thicker or thinner than another, but if the R-value is the same both materials will insulate equally
  • R-value testing is done in a 70 F environment with no air movement. Ironically enough, when you need insulation the most you’re generally not in these ideal temperatures or conditions. This can result in the rated house insulation R value being higher than the actual effective R value
  • House R-value is much lower if air or water/moisture leaks are present
  • The required R-value for house insulation depends on climate and temperature
  • 1 inch of insulation is equal to approximately 30 inches of concrete
  • House Insulation R value of Blown in Cellulose Insulation is 3.70 per inch
  • House Insulation R value of Fiberglass Insulation is 3.14 per inch
  • House Insulation R value of Expanded Polystyrene is 4.00 per inch

To learn more about R-value visit:

http://www.greenbuildingadvisor.com/blogs/dept/musings/understanding-r-value

http://www.diamondliners.com/articles/58,1.html

We recommend one of these insulation types

Closed cell foam
Uses: Walls

Application: 1” thick layer in the stud cavity with R6, followed by R13 fiberglass bat for a total of R19

Advantages: great air seal, great moisture seal, made of vegetable oil, high R value

Disadvantages: dries very hard, makes it hard for electricians to do wiring

Open cell foam
Uses: Walls

Application: 3-1/2” thick layer in the stud cavity for a total of R15

Advantages: great air seal, easier to pull wires through and to do new framing, made of Castrol bean oil, no cure time

Disadvantages: moisture seal is not as good as Closed Cell, lower and inconsistent R-values

Cellulose insulation
Uses: Walls

Applied in open studs

Advantages: inexpensive, great air seal

Disadvantages: only R13 can be used on 2×4 walls, needs 48 hours cure time before drywall installation


Fiberglass bats
Used in: walls and crawlspaces

Applied between stud from R-13, R15 and R19 rolls.

Advantages: inexpensive

Disadvantages: poor air seal

Blown in wall insulation
Uses: Walls

Application: Blow into existing stud cavities between wall sheathing and drywall

Advantages: can insulate existing walls with minimal damage

Disadvantages: Cost, low R-value, plugs are visible from exterior

Blown in attic insulation
Uses: Attic

Application: Blow onto floor of attic, 12 inches thick equals R38

Advantages: low cost, great air seal

Disadvantages: Can’t use attic for storage


Closed cell attic insulation
Uses: Attic

Application: Apply to underside of roof deck between rafters

Advantages: great air seal, great moisture seal, controlled attic conditions for storage

Disadvantages: Cost, baffles need to be installed, if HVAC equipment is in the attic fire barrier must be installed at additional cost.

 

Natural ventilation

Natural ventilation is the process of supplying and removing air through an indoor space without using mechanical systems. It refers to the flow of external air to an indoor space as a result of pressure or temperatures differences. There are two types of natural ventilation occurring in buildings: wind driven ventilation and stack ventilation. While wind is the main mechanism of wind driven ventilation, stack ventilation occurs as a result of the directional buoyancy force that results from temperature variation.

The static pressure of air is the pressure in a free-flowing air stream and is depicted by isobars in weather maps. Differences in static pressure arise from global and microclimate thermal phenomena and create the air flow we call wind. Dynamic pressure is the pressure exerted when the wind comes into contact with an object such as a hill or a building and it is characterized by the following equation:

where (using SI units):

= dynamic pressure in pascals,
= fluid density in kg/m3 (e.g. density of air),
= fluid velocity in m/s.

The impact of wind on a building affects its ventilation and infiltration rates and the associated heat losses or heat gains. Wind speed increases with height and is lower near the ground due to frictional drag. Wind’s impact on the building form creates areas of positive pressure on the windward side of the building and negative pressure on the leeward and sides of the building. This is why building shape is crucial in creating the wind pressures that will drive air flow through its apertures. In practical terms wind pressures will vary considerably and this variance will create complex air flows and major turbulence by its interaction with environmental elements (trees, hills, etc.) and with the urban context (buildings, structures,etc.). Vernacular and traditional buildings in different climatic regions rely heavily on natural ventilation for maintaining thermal comfort conditions in the enclosed spaces.

Insulation system design

Design guidelines are offered in the UBC (Uniform Building Code), building regulations and other related literature and include a variety of recommendations on many specific areas such as:

  • Building location and orientation
  • Building form and dimensions
  • Indoor partitions and layout
  • Window typologies, operation, location, and shapes
  • Other aperture types (doors, chimneys)
  • Construction methods and detailing (infiltration)
  • External elements (walls, screens)
  • Urban planning conditions

The following design guidelines are selected from the Whole Building Design Guide, a program of the NIBS (National Institute of Building Sciences):

  • Maximize wind-induced ventilation by siting the ridge of a building perpendicular to the summer winds
  • Widths of naturally ventilated zone should be narrow (max 13.7 m [45 feet])
  • Each room should have two separate supply and exhaust openings. Locate exhaust high above inlet to maximize stack effect. Orient windows across the room and offset from each other to maximize mixing within the room while minimizing the obstructions to airflow within the room.
  • Window openings should be operable by the occupants
  • Consider the use of clerestories or vented skylights.

Wind driven ventilation

Wind driven ventilation depends on wind behavior, on the interactions with the building envelope and on openings or other air exchange devices such as inlets or chimneys. For a simple volume with two openings, the cross wind flow rate can be calculated using the following equation:]

Q=Uwind√((Cp1-Cp2)/(1/A12C12)+(1/A22C22) (1)

The knowledge of the urban climatology i.e. the wind around the buildings is crucial when evaluating the air quality and thermal comfort inside buildings as air and heat exchange depends on the wind pressure on facades. As we can see in the equation (1), the air exchange depends linearly on the wind speed in the urban place where the architectural project will be built. CFD (Computational Fluid Dynamics) tools and zonal modeling is usually used to design naturally ventilated buildings. Wind catchers are able to aid wind driven ventilation by directing air in and out of buildings.

Some of the important limitations of wind driven ventilation:

  • Unpredictability and difficulties in harnessing due to speed and direction variations
  • The quality of air it introduces into buildings may be poor due to pollution, for example due to proximity to an urban or industrial area
  • May create a strong draught and discomfort

Stack driven ventilation

(For more details, see Stack effect)

The stack effect used for high-rise natural ventilation

Stack effect is temperature induced. When there is a temperature difference between two adjoining volumes of air the warmer air will have lower density and be more buoyant thus will rise above the cold air creating an upward air stream. Forced stack effect in a building takes place in a traditional fire place. Passive stack ventilators are common in most bathrooms and other type of spaces without direct access to the outdoors.

To adequately ventilate buildings using the stack effect, the inside and the outside temperatures must be different so that warmer indoor air will rise and exit the building at higher apertures, while the colder and denser air from the exterior enters the building through its lower level openings. Stack effect increases with greater temperature differences and increased height between the higher and the lower apertures. The neutral plane in a building occurs at the location between the high and low openings at which the internal pressure will be the same as the external pressure (in the absence of wind). Above the neutral plane, the air pressure will be positive and the air will rise. Below the neutral plane the air pressure will be negative and the external air will be drawn into the space.

Stack ventilation benefits:

  • Doesn’t rely on wind so it works on still and hot summer days when most needed
  • Stable air flow (compared to wind)
  • Greater control in choosing areas of air intake
  • Sustainable ventilation method

Stack ventilation limitations:

  • Lower magnitude compared to wind ventilation
  • Relies on temperature differences (inside/outside)
  • Design restrictions (height, location of apertures) and may incur extra costs (ventilator stacks, taller spaces)
  • The quality of air it introduces in buildings may be polluted for example due to proximity to an urban or industrial area

Natural ventilation in buildings relies mostly in wind pressure differences but stack effect can augment this type of ventilation and partly restore air flow rates during hot, still days. Stack ventilation can be implemented in ways that air inflow in the building does not rely solely on wind direction. In this respect it may provide improved air quality in some types of polluted environments such as cities. For example air can be drawn through the backside or courtyards of buildings avoiding the direct pollution and noise of the street facade. Wind can augment the stack effect but also reduce its effect depending on its speed, direction and the design of air inlets and outlets. Therefore prevailing winds must be taken into account when designing for stack effect ventilation.

Estimating stack effect ventilation

The natural ventilation flow rate can be estimated with this equation:

English units:

QS

= Stack vent airflow rate, ft³/s

A

= cross-sectional area of opening, ft² (assumes equal area for inlet and outlet)

Cod

= Discharge coefficient for opening (typical value is 0,62)

g

= gravitational acceleration, around 32.2 ft/s² on Earth

Had

= Height from midpoint of lower opening to neutral pressure level (NPL), ft

NPL

= location/s in the building envelope with no pressure difference between inside and outside (ASHRAE 2001, p.26.11) American Society of Heating, Refrigerating and Air conditioning Engineers

TI

= Average indoor temperature between the inlet and outlet, °R

TO

= Outdoor temperature, °R

SI units:

where:

QS

= Stack vent airflow rate, m³/s

A

= cross-sectional area of opening, m² (assumes equal area for inlet and outlet)

Cod

= Discharge coefficient for opening (typical value is 0.62)

g

= gravitational acceleration, around 9.81 m/s² on Earth

Had

= Height from midpoint of lower opening to neutral pressure level (NPL), m

NPL

= location/s in the building envelope with no pressure difference between inside and outside (ASHRAE 2001, p.26.11)

TI

= Average indoor temperature between the inlet and outlet, K

TO

= Outdoor temperature, K

Measuring insulation performance

One way to measure the performance of a naturally ventilated space is to measure the air changes per hour in an interior space. In order for ventilation to be effective, there must be exchange between outdoor air and room air. A common method for measuring ventilation effectiveness is to use a tracer gas. The first step is to close all windows, doors, and openings in the space. Then, a tracer gas is added to the air. The reference, American Society for Testing and Materials (ASTM) Standard E741: Standard test method for determining air change in a single zone by means of a tracer gas dilution, describes which tracer gases can be used for this kind of testing and provides information about the chemical properties, health impacts, and ease of detection. Once the tracer gas has been added, mixing fans can be used to distribute the tracer gas as uniformly as possible throughout the space. To do a decay test, the concentration of the tracer gas is first measured when the concentration of the tracer gas is constant. Windows and doors are then opened and the concentration of the tracer gas in the space is measured at regular time intervals to determine the decay rate of the tracer gas. The airflow can be deduced by looking at the change in concentration of the tracer gas over time. For further details on this test method, refer to ASTM Standard E741.

Ventilation architecture

An air handling unit is used for the heating and cooling of air in a central location.

Ventilating (the V in HVAC) is the process of “changing” or replacing air in any space to provide high indoor air quality (i.e. to control temperature, replenish oxygen, or remove moisture, odors, smoke, heat, dust, airborne bacteria, and carbon dioxide). Ventilation is used to remove unpleasant smells and excessive moisture, introduce outside air, to keep interior building air circulating, and to prevent stagnation of the interior air.

Ventilation includes both the exchange of air to the outside as well as circulation of air within the building. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. The two principal building ventilation methods are mechanical/forced and natural.

“Mechanical” or “forced” ventilation is used to control indoor air quality. Excess humidity, odors, and contaminants can often be controlled via dilution or replacement with outside air. However, in humid climates much energy is required to remove excess moisture from ventilation air.

Kitchens and bathrooms typically have mechanical exhaust to control odors and sometimes humidity. Factors in the design of such systems include the flow rate (which is a function of the fan speed and exhaust vent size) and noise level. If ducting for the fans traverse unheated space (e.g., an attic), the ducting should be insulated as well to prevent condensation on the ducting. Direct drive fans are available for many applications, and can reduce maintenance needs.

Ceiling fans and table/floor fans circulate air inside a room which reduces the perceived air temperature because of evaporation of perspiration on the skin of the occupants. Because hot air rises, ceiling fans may be used to keep a room warmer in the winter by circulating the warm stratified air from the ceiling to the floor. Ceiling fans do not provide ventilation as defined as the introduction of outside air.

Natural ventilation

Natural ventilation is the ventilation of a building with outside air without the use of a fan or other mechanical system. It can be achieved with operable windows or trickle vents when the spaces to ventilate are small and the architecture permits. In more complex systems warm air in the building can be allowed to rise and flow out upper openings to the outside (stack effect) thus forcing cool outside air to be drawn into the building naturally through openings in the lower areas. These systems use very little energy but care must be taken to ensure the occupants’ comfort. In warm or humid months, in many climates, maintaining thermal comfort solely via natural ventilation may not be possible so conventional air conditioning systems are used as backups. Air-side economizers perform the same function as natural ventilation, but use mechanical systems’ fans, ducts, dampers, and control systems to introduce and distribute cool outdoor air when appropriate.

Standards

For standards relating to ventilation rates, in the United Stated refer to ASHRAE Standard 62.1-2010: Ventilation for Acceptable Indoor Air Quality. These requirements are for “all spaces intended for human occupancy except those within single-family houses, multifamily structures of three stories or fewer above grade, vehicles, and aircraft. In the revision to the standard in 2010, Section 6.4 was modified to specify that most buildings designed to have systems to naturally condition spaces must also “include a mechanical ventilation system designed to meet the Ventilation Rate or IAQ procedures [in ASHRAE 62.1-2010]. The mechanical system is to be used when windows are closed due to extreme outdoor temperatures noise and security concerns. The standard states that two exceptions in which naturally conditioned buildings do not require mechanical systems are when:

  • Natural ventilation openings that comply with the requirements of Section 6.4 are permanently open or have controls that prevent the openings from being closed during period of expected occupancy, or
  • The zone is not served by heating or cooling equipment.

Also, an authority having jurisdiction may allow for the design of conditioning system that does not have a mechanical system but relies only on natural systems. In reference for how controls of conditioning systems should be designed, the standard states that they must take into consideration measures to “properly coordinate operation of the natural and mechanical ventilation systems”.

Another reference is ASHRAE Standard 62.2-2010: Ventilation and Acceptable Indoor Air Quality in low-rise Residential Buildings. These requirements are for “single-family houses and multifamily structures of three stories or fewer above grade, including manufactured and modular houses,” but is not applicable “to transient housing such as hotels, motels, nursing homes, dormitories, or jails.”

Standards relating to ventilation rates in the United Stated are described in ASHRAE Standard 55-2010: Thermal Environmental Conditions for Human Occupancy. Throughout its revisions its scope has been consistent with its currently articulated purpose, “to specify the combinations of indoor thermal environmental factors and personal factors that will produce thermal environmental conditions acceptable to a majority of the occupants within the space.” The standard was revised in 2004 after field study results from the ASHRAE research project, RP-884: developing an adaptive model of thermal comfort and preference, indicated that there are differences between naturally and mechanically conditioned spaces with regards to occupant thermal response, change in clothing, availability of control, and shifts in occupant expectations. The addition to the standard, 5.3: Optional Method For Determining Acceptable Thermal Conditions in Naturally Ventilated Spaces, uses an adaptive thermal comfort approach for naturally conditioned buildings by specifying acceptable operative temperature ranges for naturally conditioned spaces. As a result, the design of natural ventilation systems became more feasible, which was acknowledged by ASHRAE as a way to further sustainable, energy efficient and occupant friendly design.

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