Solar Home Design and Thermal Mass

Solar Home Design

And

Simulation of Thermal Mass

Stefan Fortuin

fortland@gmail.com

Papers

Renewable Energy System Design

Renenwable En Conversion Devices

Energy Policy

Greenhouse Science and Policy

Source: http://jc-solarhomes.com/five.htm

Five Solar Thermal Principles

See document design for the sun!! 1. Heat Gain

Heat gain refers to the heat accumulated from the sun: Solar-thermal-heat is trapped using the greenhouse effect. The ability of a glazing surface to transmit short wave radiation and reflect long wave radiation is known as the greenhouse effect.

2. Heat Transfer Heat is transferred by conduction or convection. Convection: hot portions of a liquid or gas

will rise and cold portions above it will sink. Conduction rate of heat transfer has to do with the conductivity of the medium and the temperature differences.

3. Heat Storage Heat transfer to a storage medium can be maximized with the aid of a multi tank heat storage

vault system.

4. Heat Transport Heat transport from solar collector to heat storage vault. In cold climates it is important to

separate the heat collection area from heat storage area. Closed loop systems use a circulator pumps to transport heat from sun to storage vault. Warm climates use simple batch heaters, water tanks enclosed inside glazed boxes.

5. Heat Insulation A solar home is worthless without adequate insulation: About R25 in the walls and R35 in the

roof/ceiling area. Heat storage vaults and heat transport tubing should also be well insulated. Sunrooms must be isolated from living quarters with doors or drape to prevent heat loss at night.

Source: http://jc-solarhomes.com/five.htm

Energy End-use in NZ Houses

Source: BRANZ 1998, Conf. paper NO.57

Energy End-use in NZ Houses

Source: BRANZ 1998, Conf. paper NO.59

Energy-wise Renewables 11

Passive Solar Designfor NZ Homes:

Since solar energy is free, why arent many

more homes in New Zealand designed to use

passive solar principles to provide space [or

water] heating?

Source: EECA

Seasonal Sun Path

Source: EECA: Energy-wise Renewables 11: Passive Solar Design for New Zealand

Solar Room Orientation

Source: EECA: Energy-wise Renewables 11: Passive Solar Design for New Zealand. Adapted from David Pearsons The New Natural House Book.

Parameters

Reflection (%) Thermal Mass

Thermal Conductance (K-Value)

Source: EECA/Waitakere CC: Design for the Sun

Solar Heat Gain

Radiation Conduction Convection

Source: EECA/Waitakere CC: Design for the Sun

Solar Heat Gain Checklist

Source: EECA/Waitakere CC: Design for the Sun

Ensure that north windows will allow direct sun onto thermal mass for 6 hours on a sunny winters day,

Given the right combination with insulation and thermal mass, the area of north-facing glazing should be about 10-20% of the houses floor area . (You can calculate the area using EECAs Energy Wise Design for the Sun manual to balance the rate of heat loss (dependent on insulation) with thermal mass and local climate)

Windows on east or west walls would ideally be 2-5 % of total floor area.

On a south wall windows should be the minimum necessary for adequate ventilation and light. Consider the use of clerestorey windows (above the roofline) to bring sun and light into south-facing rooms.

For a complex house design, or on a south-facing slope, consider a mix of passive solar systems, using direct, indirect and isolated heat gain where each is appropriate.

Eaves or other overhangs prevent overheating by the high summer sun. The average window works well with a 400-500mm overhang, while glass doors require 700-900mm depending on wall height and orientation.

Be very careful with the design of a conservatory. It is likely to overheat in summer unless you build in ventilation and shade, and on winter nights it could leak heat massively if it cannot be sealed off from the rest of the house. The value of a conservatory is in the quality of living space it offers. Ensure that it is also thermally efficient, not a thermal drain.

Solar Heat Gain Checklist

In Pictures

Source: EECA/Waitakere CC: Design for the Sun

Solar Heat Storage Checklist

Source: EECA/Waitakere CC: Design for the Sun

Choose or create site conditions suitable for a solid concrete floor for solar heat storage. The floor offers the best opportunity for thermal and economic performance.

A large thermal mass may slow down morning heating up, and too little mass does not store sufficient energy. So choose the correct size of thermal mass. It is possible to calculate your requirement exactly by balancing it with the solar gain and insulation of the house. Alternatively you can use the rules-of thumb that follow.

A concrete floor slab should be about 100 mm thick, exposed to direct sunlight, dark in colour,.and insulated underneath.

A masonry wall (e.g. brick, concrete, block, etc) should be 100 to 150mm thick, and insulated on the outside.

Avoid covering up thermal mass floors with carpet because it reduces the rate of heat absorption. In places where you will be sitting with your feet on the floor you can use rugs for comfort.

Avoid air cavities in thermal mass (e.g. fill concrete block cavities). Avoid thermal mass walls in shady areas unless they are well insulated. They will lose too

much heat to the outside, without giving the benefit of absorbing the suns heat. Internal thermal mass walls are better than external as they dont lose heat to the outside at

night. However external walls will usually get more sun and offer the most practical solution. A thermal wall of half height will offer some thermal storage while still allowing a view. Make a thermal mass wall into a feature wall. Build it with ornamental stone, artistic earth,

patterned bricks, etc.

Large Day/Night temperature fluctuations may require active intervention twice a day to maximize passive systems.

Solar: Active

Source: EECA/Waitakere CC: Design for the Sun

Solar: Active

Source: www.greenbuilder.com

Trombe Wall Thermal Chimney

Insulation

Thermal Mass

Thermal Mass & Insulation

Hot Box Test

Insulation (I)

Thermal Mass (M)

Insulation - Thermal Mass (IM)

Thermal Mass - Insulation (MI)

Th. Mass - Insulation Th. Mass (MIM)

Insulation Th. Mass - Insulation (IMI)

Envelope configurations:

Source: www.ornl.gov roofs and walls

Thermal Mass & Insulation

Source: EECA/Waitakere CC: Design for the Sun

Thermal Mass & Insulation:

Example of Central Thermal Mass

Source: www.solarserver.de

Day/Night Influence of Thermal

Mass

Basics of Building Insulation

Vapor barrier Some insulation products absorbing moisture can easily loose up to 50% of its

thermal efficiency.

Radiation 65% to 80% of all energy that goes from the warm side to the cold side of a wall

assembly, summer and winter, is radiant heat.

Eflective products, on the other hand, stop approximately 70 % of all radiant heat by reflecting up to 97% of the radiant heat rays.

Conduction Stagnant air is a better insulation than any solid material

Conventional thermal insulation does not stop heat rays; but rather, will absorb them and transfer heat. Thus, mineral wool and other thermal insulation will only slow down the transfer of heat.

Convection/Ventilation Air Changes per Hour (ACH) The number of times one house volume of air leaks

through the house in one hour. Test: (de)pressurize a house with ablower to a pressure difference of 50 Pascals and

then measure the flow through the blower. Measure the internal air volume of the house and divide.

Energy Storage Options

Energy Generation Options

Advanced Materials

Aerogel (foamed glass)

Thermal conductivity 0.003 W/m.K (90-

99.8% air)(0.024 W/m.K for Air)

(0.04 W/m.K for fibre glass/wool)

Phase Change Materials (PCM)

Hydrides (liquid-solid)

Fatty acids and esters (liquid-solid)

paraffin (liquid-solid)Used in Wallboard!

Phase Change Material

Phase Change Wallboard

Source: http://eetdnews.lbl.gov/cbs_nl/nl16/phase.html

Next:

Read: Energy-wise Design for the sunManual

Design a house (architect)

Model the House using ALF 3

Determine Renewable Energy supply at the Site

Evaluate performance

Remodel (iterate)

BRANZ ALF 3

ALF 3 Software, Manual, House Insulation Guide

Adopted as Compliance Method for NZBC Clause H1 Energy Efficiency

Demonstrate the effect of varying:

Insulation (loss)

Location and Size of Windows (gain)

Thermal Storage

Annual Loss Factor 3 (ALF)

Source: BRANZ No 51

Problems / Limitations

Thermal Performance (Utilizable gain) depends on: Requirements of the occupants / design / materials

(pre-build)

Behaviour of the occupants (post-build) Ventilation, air-tightness

Heating schedule intermittent heating favours light weight building, not high

thermal mass

Available resources / Renewable energy Climate

Effective Thermal Mass

Effect of Thickness

Source: BRANZ No 51