2015-10-19

1

Passive Solar Design and Concepts

Daylighting

2015-10-19

2

Winter

Summer

Passive Solar Heating

Good architecture?

The judicious use of south glazing coupled with appropriate shading and thermal mass.

Passive solar

• Direct (or indirect) gain of solar energy through windows or in attached sun-spaces for space heating

• high performance fenestration and/or transparent insulation

• application of thermal mass for storage and to reduce overheating

• can include natural ventilation

• design for maximization of natural Daylighting

• Apply design principles to increase heat gain and reduce cooling loads

Good architecture and energy conservation!

2015-10-19

3

Sun Position and Chart

Seasonal Variation in sun-altitude

Solar Radiation Definitions

Global solar irradiance

and its components

The radiation from the sun that meets the earth without any change in

direction is called direct or beam radiation, Gdir.

The radiation from the sun after its direction has been changed by

scattering in the atmosphere is called diffuse radiation, Gdif.

The radiation from the sun after it is reflected on the ground is called the

ground reflected radiation, Gref.

The sum of the beam, diffuse and reflected solar radiation on a surface

is called the global solar irradiance, GG.

GG= Gdir + Gdif + Gref

From “Planning and Installing Solar Thermal Systems”, James & James/Earthscan, London, UK

2015-10-19

4

Solar Spectrum

Sun spectrum AM 0 in space and AM 1.5 on the earth with

a sun elevation of 41.8o

From “Planning and Installing Solar Thermal Systems”, James & James/Earthscan, London, UK

Solar irradiance outside atmosphere

Direct solar irradiance at sea level

Solar Radiation

Global solar irradiance and its components with different

sky conditions

From “Planning and Installing Solar Thermal Systems”, James & James/Earthscan, London, UK

2015-10-19

5

ipreciado.wordpress.com

2015-10-19

6

Direct or Indirect Passive solar Gain

www.greenandpractical.com

Direct gain Indirect gain

2015-10-19

7

www.homepower.com

Traditional Passive Solar Design (Direct Gain)

http://www.solar365.com

• Direct Solar Gain –South Glazing (clearstory windows)

2015-10-19

8

Passive solar design at York University

Passive Solar Heating

Mass walls and (transparent) Insulation

2015-10-19

9

Passive Solar Heating/Cooling

Fenestration

The location and operation of shading

Interior Shade

Exterior Shade

Attached Sunspaces

Attached Sun Space

Photo Credit: Pamm McFadden (NREL Pix)

Passive Solar Heating on Residence, France

2015-10-19

10

Mass Wall

Indirect Passive Solar Concepts

Trombe Wall (Indirect Passive Solar)

http://www.smartshelterresearch.com/23-passive-solar-schools/

2015-10-19

11

Storage Walls

A storage wall (e.g. Trombe wall) is a sun-facing wall built from

material that can act as a thermal mass (such as stone, concrete,

adobe or water tanks), combined with an air space, insulated

glazing and vents to form a large solar thermal collector.

During the day, sunlight would

shine through the glazing and warm

the surface of the thermal mass. At

night, if the glazing insulates well

enough, and outdoor temperatures

are not too low, the average

temperature of the thermal mass

will be significantly higher than

room temperature, and heat will

flow into the house interior.

From “Solar Engineering of Thermal Processes”, Duffie & Beckman

Energy flows through direct-gain vs collector storage wall as a function of time of day

2015-10-19

12

http://cleantechnica.com

2015-10-19

13

Passive Solar Examples

Involves the direct use of sunlight for daylighting and space heating

2015-10-19

14

Window Performance

Passive Solar Heating

Advanced fenestration

2015-10-19

15

Canadian Energy Rating System

Canadian Energy Rating System was designed to show the average heating season thermal performance of windows. The Energy Rating procedure is incorporated in the Canadian Standard A-440.2-98, “Energy Performance of Windows and Other Fenestration Systems.” The Energy

Rating (ER) combines the effects of U-value, SHGC and air leakage characteristics of windows.

ER = solar heat gains – conductive heat losses – air leakage heat losses

ER = 0.8 * 72.2 * SHGCw – 21.9 * Uw – 0.54 * (L75 / Aw)Where,

ER is Energy Rating, W

SHGCw – Solar heat gain coefficient of a window

• The Solar Heat Gain Coefficient (SHGC) is the percent of solar energy incident on the glass that is transferred indoors both directly and indirectly through the glass. The direct gain portion is the solar energy transmittance, while the indirect is the fraction of solar energy incident on the glass that is absorbed and re-radiated or transmitted through convection indoors. For example, 1/8" (3.1 mm) uncoated clear glass has an SHGC of approximately 0.86, of which 0.84 is direct gain (solar transmittance) and 0.02 is indirect gain (convection / re-radiation). – (See more at: https://www.guardian.com/commercial/ToolsandResources

Uw – Overall heat loss coefficient, W/(m2oC)

72.2 represent the average solar radiation on a vertical window during the heating season, (W/m2)

0.8 factor is to account for exterior shadings on windows.

21.9 represents average temperature difference over the heating season.

Canada has a variety of weather patterns – ranging from mild climate in southern BC to very cold northern regions. Therefore, there have been a number of situations arising in certain mild regions as well as with window designs in which the ER values do not seem to reflect the use of better fenestration technologies (such as low-E, argon-filled, insulated spacer and so on). This has been identified as a major obstacle in acceptance of the Energy Rating system. Again, the issue is not the technical soundness of the ER equation but the proportional contribution of the solar effects and insulating effects. Manufacturers can voluntarily rate energy performance of windows using the services of Canadian Standards Association.

See also https://en.wikipedia.org/wiki/Solar_gain

Passive or Active?

Mass

Wall

OOPS! No storage

2015-10-19

16

Simple Example Model

Polystyrene Insulation

Double Pane Vertical Window

Concrete Patio Stone Floor (painted black)

Why Store Energy?

• solar energy is a time-dependent energy resource

• load does not match available energy

• cost consideration (avoid peak use)

• short term or long term storage

A solar energy process with storage. (a) Incident solar energy, GT, collector useful

gain, QU, and loads, L, as a function of time for a 3 day period.

From “Solar Engineering of Thermal Processes”, Duffie & Beckman

2015-10-19

17

Air Based Thermal Storage

An air based thermal storage

(e.g. Solarwall, InSpire Wall)

pre-heats the outside air

before it enters the building to

provide fresh air changes and

natural humidification.

Source: http://www.rockymtsolar.com/ Source: http://oee.nrcan.gc.ca/

Packed-bed Storage

A packed bed is a large insulated container filled with

loosely packed rocks a few centimeters in diameter.

Circulation of air through the void of the packed bed

rocks results in natural or forced convection between

the air and the rocks.

From “Solar Engineering of Thermal Processes”, Duffie & Beckman

Direction

of flow

2015-10-19

18

Modes of Operation

From “Solar Energy Engineering”, Jui Sheng Hsieh

Mode 1 – Charging Mode

When the sun is shining but there is no space heating demand, hot

air from the collector enters the top of the storage unit and heats up

the rock bed. As the air flows downward, heat transfer between the

air and the rocks results in a stratified temperature distribution of the

rock bed, being the hottest at the top and the coolest at the bottom.

The cool air then returns to the collector to be heated.

Charging Mode

From “Solar Engineering of Thermal Processes”, Duffie & Beckman

High stratification due to high heat transfer coefficient-area

product, UA.

2015-10-19

19

Modes of Operation

From “Solar Energy Engineering”, Jui Sheng Hsieh

Mode 2 – Discharging Mode

When no solar energy can be collected but there is a heating

demand, hot air is drawn from the top of the rock bed into the house

and cooler air from the house is returned to the bottom of the bed,

causing the bed to release its stored energy. (Note: Charging and

discharging a pack-bed storage cannot be executed at the same

time! This is in contrast to water storage systems.)

Modes of Operation

From “Solar Energy Engineering”, Jui Sheng Hsieh

Mode 3 – Auxiliary Mode

When there is sunshine and at the same time load demand, hot air from

the collector is led directly into the house and cooler air from the house

is led directly into the collector, both bypassing the storage unit. The

auxiliary heater shown in the figure can be used to remedy the energy

deficiency of the collector or the storage to meet the loads. Through the

by-pass route, the auxiliary heater alone can be called upon to meet the

entire energy demand.

100%

Auxiliary

2015-10-19

20

Horizontal Flow Rock Bed

From “Solar Energy Program, A Guide to Rock Bed Storage Units”, Enermodal Engineering Limited

Baffles (used to

increase flow path)

Sensible Heat Storage Materials

From “Solar Energy Engineering”, Jui Sheng Hsieh

* Water has three times the heat capacity of rock on a volume basis,

meaning that rock requires three time more volume than water to store

the same amount of sensible heat!

2015-10-19

21

Energy CalculationsEnergy Equation: Energy needed to heat hot water is Q

Q = Vol x Density x Specific Heat x Temperature Rise = kJ

Or

Units Check

Q = (L) x kg/L x kJ/kg°C x °C = kJ

The (constant pressure) specific heat of water or Cp is the amount of energy (KJ) required to heat one Kilogram of water 1 degree Celcius or (Kelvin). This value is not constant but varies slightly with temperature, e.g.,

Properties of Water

955

965

975

985

995

1005

0 10 20 30 40 50 60 70 80 90 100

Temperature, oC

De

ns

ity

, k

g/m

3

4.15

4.16

4.17

4.18

4.19

4.2

4.21

4.22

4.23

4.24

4.25

Sp

ec

ific

He

at

(k

J/k

goC

)

993.4 kg/m3

4.181 kJ/kg oC

35

Range

Specifc heat and density of water

For our purposes, over the temperature range considered, we can assume the value of thespecific heat and density of water is effectively fixed at the average values given above.

2015-10-19

22

Example Cal’c.

• Example: What is the energy required to heat a 270 L tank from 15°C to 55°C

• For this example the following is assumed to be true: • The density of water is 0.993, Cp = 4.181

• (1 litre of water is equal to 0.993 kg)

• The price of electricity is $ 0.35 kWh

• 1 Joule is equal to a Watt second (i.e., J = Ws)

• ∆T = 40

Q = 270 L x 0.993 kg/L x 4.181 kJ/kg°C x 40°C

= 44,838.7 kJ or 44.8 MJ

In kilowatt hours this much energy is:(Note that one Joule of energy is a Watt of power operating for one second or a Ws)

Therefore

Q= 44,838.7 kJ = 44,838.7 kWs

= 44,838.7 kWs x( 1 hr/3600 s)

= 44,838.7/3600

= 12.45 kWh

At an electrical energy cost of $035/kWh, this energy costs:

Cost = $035/kWh x 12.45 kWh = $4.35

2015-10-19

23

Phase Change Storage

When a substance undergoes a solid-liquid phase transition,

it usually involves a large amount of latent heat with a small

volume change.

A phase change storage would be a space-saver if it

satisfies the following conditions:

1) the phase transition must occur at a temperature

compatible with the heating and cooling load requirement

2) the process must be reversible over a large number of

cycles without degradation

3) the material must be inexpensive and can be used safely

A few salt hydrates (salts bonded to water molecules)

possess the desired qualities to serve as phase-change

materials (PCMs).

For Phase Change

v

Temperature

En

tha

lpy

Dh

2015-10-19

24

Storage Media

From “Thermal Energy Storage for Solar and Low Energy Buildings”, IEA Solar Heating and Cooling Task 32