Active Solar Thermal Energy Applications in Buildings (Part 1)

Yerevan State University of Architecture and Construction

INOGATE Programme New ITS Project, Ad Hoc Expert Facility (AHEF) Task AM-54-55-56

Slides prepared by: Xavier Dubuisson Eng. MSc. XD Sustainable Energy Consulting Ltd.

Table of Contents

Part 1

• Solar Energy Resource in Armenia

• Systems and Components

• Thermosiphon Systems

Part 2

• Designing Solar Thermal Systems

• Typical System Configurations

• Installation and Commissioning

• Financial Analysis

• Solar thermal applications in Armenia

• Further References

THE SOLAR ENERGY RESOURCE

Solar Trajectory

2-3 Solar Resources - Solar Radiation

Summer solstice

90° - latitude + 23 °

Equinox

90° - latitude

Winter solstice

90° - latitude - 23 °

To find out solar position & intensity at your location: http://www.nrel.gov/midc/solpos/solpos.html

Maximum elevation angle (height of the sun at solar noon): ϒS

Calculating the Sun’s Position

ζ = 900 − α

Source: Pveducation.org

∝: elevation angle ζ: zenith angle 𝜑: latitude 𝛿: declination angle

In northern hemisphere: ∝ = 90 − 𝜑 + 𝛿

(1)

Where B = 360/365 (d-81) in degrees and d is number of days since the beginning of year

(2)

Local Standard Time Meridian

Equation of time

Time correction factor

Hour angle

Where ∆𝑇𝐺𝑀𝑇 is difference between local time and Greenwich mean time in hours

Calculating the Sun’s Position

Local solar time

Declination angle

Azimuth

Elevation

Calculating the Sun’s Position

Source: http://www.gaisma.com/en/location/yerevan.html

Elevation angle Azimuth angle

http://www.gaisma.com/en/location/yerevan.html

Calculating solar radiation on a tilted surface

Elevation angle

Panel tilt

Atmospheric Effects – Air Mass Factor

Air mass factor (AM) = 1/sin ϒS (ϒS: Elevation angle)

Sun elevation at noon over the course of one year at lat. 52 °N

Source: Earthscan, 2010

Source: PVEducation.org

Air Mass / Radiation intensity

Effect of elevation angle on attenuation of irradiation Source: Earthscan, 2010

Id: direct irradiance (kW/m2)

1.353 kW/m2 = solar constant 0.7 (% of radiation incident to atmosphere transmitted to earth) a = 0.14, h = height above sea level (km) 0.678 is an empirical fit to observed data

IG: global irradiance (kW/m2) on a clear day where

diffuse radiation is still 10% of direct radiation

Direct and diffuse radiation

Direct radiation: 60%

Diffuse radiation: 40%

Solar irradiation intensity

Irradiance

Definitions: Irradiation (kWh/m2·yr) Sunshine hours (hrs) Irradiance (W/m2) Peak sunshine hours (hrs)

Solar energy resource in Armenia

• 1720 kWh/m2,yr average in Armenia

• 1000 kWh/yr,m2 in EU

• 2500 hrs of sunshine per year

Solar energy resource in Armenia

Source: Sargsayan, 2010.

Average daily total (E1) and diffused (E2) irradiation per m2 horizontal area in Yerevan.

Annual irradiation across the globe

2-11 Solar Resources - Solar Radiation

Effect of Orientation and Inclination on Solar Irradiation

6-5 Design and Sizing

Optimal Inclination

Effect of Shading

Obstacle height Angle and Azimuth

Assessing Shading

Solar site locator ($90)

Source: http://www.solardesign.co.uk/sss.php

Assessing shading

Source: Martin Cotterell. http://www.solarpowerportal.co.uk/martins_blog/sun_path_diagrams_and_shade_lines_2356

iPV iPhone solar app: http://www.solmetric.com/solmetricipv.html

SunEye by Solmetric ($2000 + $600 for software). Source: http://www.solmetric.com

Assessing Shading

http://www.solarpathfinder.com

Approx. $300

SYSTEMS AND COMPONENTS

Active Solar Thermal Energy in Buildings

Solar water heater advertisement, 1902,..Source:..http://en.wikipedia.org/wiki/Solar_water_heating

Solar Thermal System Components

Flat Plate Collectors

A: Glazing/ Solar Glass B: Copper or Aluminium Absorber sheet

C: Powder Coated Aluminium Frame D: Collector Pipe

E: Mineral Wool Insulation F: Meander Tube

G: Selective Coating H: Bottom Plate (Aluminium)

I: Secure Glass Fixing J: Revolving Groove for Assembly

Evacuated Tube Collectors Heat Pipe

Source: www.kingspansolar.ie

Tube-manifold connection

Absorber plate

Absorber support clip

Evacuated glass tube

End support bung

Evacuated Tube Collectors Direct Flow

Evacuated Tube Collectors Sydney tube with concentrator

“Sydney” double-walled glass tube

Feeder

Outer glass tube Heat conducting plate Return

Inner glass tube w. absorber coating

Reflector

Evacuated space

Vacuum tubes versus flat plate

Advantages

• Higher operating temperatures than flat plate

• Reduced heat losses

• Higher yield per m2 of collector than flat plate (attractive where space is an issue)

• Compact and sealed construction, high protection of absorber.

Disadvantages

• High stagnation temperatures, causing more stress on pipework, insulation and solar fluid.

• Higher specific costs (€/m2 of absorber area)

• Higher cost (€/kWh) for available solar yield at medium operating temperature range.

• Possible loss of vacuum

Absorber Coating

Source: SolarPraxis, 2002

Absorption, reflection and useful heat on various surfaces

Absorption/emission spectrum Wave length λ in μm

Collectors’ reference areas

Source: SolarPraxis, 2002

(1) Absorber area

(2) Aperture area

(3) Gross area

(1) (2)

(3) (1) (2) (3)

(1) (2) (3)

Energy Balance of Solar Collectors

Conduction

Collector energy performance

QA: available thermal power (W/m2)

G: incident irradiance on the glass pane (W/m2)

GA: available irradiance at the absorber, converted into heat (W/m2)

QL: thermal losses through convection, conduction and radiation (W/m2)

𝜏: transmissivity of glass, ∝: absorptivity of absorber ∆𝜃: temp difference between absorber and the air k1: linear heat loss coefficient (W/m2,K) – for low absorber temperatures

K2: quadratic heat loss coefficient (W/m2,K2) – for higher temps, increased thermal radiation

η0 : optical efficiecny = α * τ * F; F: absorber efficiency factor

Efficiency flat plate versus evacuated tube collectors

Source: Kingspan Solar

Storage Tanks - configurations

Solar tank with fresh water coil & internal stratification device, Source: www.viessmann.de

Standard twin coil cylinder Source: Tisun

One coil cylinder with immersion heater. Source: Tisun

Solar tank part of thermosiphon system.

Heat store with external stratification device, Source: Tisun

Energy Content of Storage Tanks

Q: heat content (Wh) M: mass of water/fluid (kg) Cw: specific heat capacity of water (1.16 Wh/kgK) Δθ: temperature difference (K) Energy content in this tank, Q: = 100 kg × 1.16 Wh/kgK × 45 K + 100 kg × 1.16 kWh/kgK × 15 K + 100 kg × 1.16 Wh/kgK × 0 K = 6960 Wh

Q = mcwΔθ

Storage tank – heat loss

BAD BETTER

Equivalent to yield from 2 m2 of solar collectors

0.6 W/K (x2) 36W 0.3 W/K (x6) 54W

1.4 W/K 42W

Total = 132W

Annual losses: 1156 kWh

Storage tank – heat losses

• Storage losses can be up to 30% of total heating requirement

• Recommended insulation thickness = 20 cm (large tanks) and applied carefully (no air gaps)

• Insulation around pipe connections and fittings important

• Ratio between height/volume: 2 < H/D < 4

Storage tank - heat losses

Large tank insulation should be at least 20 cm

Multiple storage tanks result in higher heat losses. Source: AEE INTEC

Single, large, well insulated solar tanks reduce heat losses substantially. Source: AEE INTEC

Storage Tanks - stratification

Solar tank with external stratification device and fresh water coil. Source: Tisun

Illustration of stratification process. Source: Lochinvar.

Stratification by internal lance using water density variation with temperature for layering hot water inlet. Source: Solvis

Solar Circuit

Source: Viessmann

De-airing device

Pumping station

Pre-cooling vessel

Expansion tank

Collecting vessel

Temp. sensor solar panels

De-airing device

Temp. sensor solar tank

Controller Pressure relief valve

Filling/draining connections

Pumping Station

44

Source: Bosch Thermotechnik

(1) Ball valve with temperature gauge and integrated gravity brake

(2) Compression fitting

(3) Pressure relief valve

(5) Connection to solar expansion vessel

(6) Fill and drain valve

(7) Solar pump

(8) Flow rate indicator

(9) Air seperator

(10) Control/shut-off valve

Heat Exchangers

Finned tube heat exchanger

Plain tube heat exchanger

Plate heat exchanger

Tubular heat exchanger

Internal External

Sou

rce:

Ear

thsc

an, 2

01

0

Expansion Tanks

Source: www.kingspansolar.ie

As delivered (3 bar charge

pressure)

Solar circuit filled

but cool

Max pressure, highest solar fluid temp.

Solar fluid

Nitrogen

Overheating prevention

Source: http://www.kingspansolar.ie/

Heat dissipation emitter

De-airing

Source: spirotech.co.uk http://www.avg.net.au

Control - Forced Circulation

3-49 Components and Subsystems of Solar Thermal Installation

Control Operating Principle

3-50 Components and Subsystems of Solar Thermal Installation

Wide range of control strategies

Source: STECA

Sensors

3-41 Components and Subsystems of Solar Thermal Installation

Pipework and Insulation

Insulation material specifications: • resistant to water & impermeable to vapour e.g. Armaflex closed cells (when outside) • low-thermal conductivity • Protection against rodents and bird-pecking • UV resistant

Examplary insulation of ball valves, pumps

Legionella prevention

External plate heat exchanger Source: Tisun

Internal coil heat exchanger Source: Tisun

Instant fresh water heating solutions

German requirements for domestic hot water temperature

Source: AEE INTEC, 2002.

Examples of system integration

Source: www.viessmann.de

Pumping station pre-mounted on tank

Controller pre- installed

Examples of system integration

Source: Solvis.de

Burner

Stratification device

Fresh water station

Central heating feed

THERMOSYPHON SYSTEMS

Active Solar Thermal Energy in Buildings

System Configuration

4-5 Solar Thermal Installations

Components

3-4 Components and Subsystems of Solar Thermal Installation

Control

3-48 Components and Subsystems of Solar Thermal Installation

Prefabricated Solar Systems

4-2 Solar Thermal Installations