---
title: "Active and passive solar control"
subject: "Building Technology"
chapter: 1
key: "semester_6/building_technology:active-passive-solar"
source: https://www.bctengineer.com/q/semester_6/building_technology/active-passive-solar
site: BCT Engineering
---

# Active and passive solar control

Building Technology · Chapter 1: Functional Requirements of Buildings

- Asked in: 2081 Chaitra, 4 marks
- Video: [Passive Solar Design Principles](https://www.youtube.com/watch?v=YylmeMilok8) — Master Builders Victoria
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/active-passive-solar
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-1

## Question

State and explain how active and passive solar control system is achieved in building.

## Short answer

Passive solar uses design (orientation, Trombe wall, shading) without mechanical parts. Active uses devices (solar water heater, PV panels, motorized shades) with pumps or fans.

## Answer

**Solar control** means using the sun's energy for heating in cold seasons and keeping it out in hot seasons.

#### Passive solar control
Uses only the building design and natural energy flows, with no mechanical parts.
- **Orientation and layout**: Main openings face south.
- **Direct gain**: South windows let in winter sun to heat the floor and walls (thermal mass).
- **Trombe wall**: A dark masonry wall behind glass absorbs heat and releases it into the room.
- **Sunspace / greenhouse**: an attached glazed space.
- **Shading devices**: chhajja, louvres, pergolas and trees, to block summer sun.
- **Reflective roof colours, insulation and cavity walls** to cut heat gain.
- **Natural ventilation and evaporative cooling**.

```text
 Winter sun --> [glass] --> room, dark wall stores heat
 Summer sun --> blocked by overhang
```

#### Active solar control
Uses mechanical or electrical devices, with collectors and a pump or fan.
- **Solar water heater** (flat-plate collector with a circulating pump or a thermosyphon tank).
- **Solar air heater** with a fan to blow warm air into the rooms.
- **Photovoltaic panels** to give electricity for lights, fans and heat pumps.
- **Motorised shades / louvres** that follow the sun.
- **Solar-powered absorption chillers** for cooling.

Passive systems cost little and need almost no maintenance. Active systems give more control but cost more and need maintenance. The best design combines both.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Passive solar control uses
   A. Building design and natural flows only, no mechanical parts
   B. Pumps and fans
   C. PV panels
   D. Motorised shades
   Answer: A. Direct gain, Trombe wall, shading, and orientation are passive. (Key point: Passive)

2. A Trombe wall is
   A. A solar PV array
   B. A dark masonry wall behind glass that absorbs and releases heat
   C. A pump-driven collector
   D. A louvre that follows the sun
   Answer: B. It stores sun heat and releases it into the room. (Key point: Trombe wall)

3. Which is an active system?
   A. Chhajja
   B. Direct gain window
   C. Flat-plate solar water heater with pump
   D. Pergola
   Answer: C. Active systems use collectors with pump or fan. (Key point: Active)

4. Compared with active, passive systems
   A. Cost more and need much maintenance
   B. Give more control
   C. Need electricity
   D. Cost little and need almost no maintenance
   Answer: D. Active gives more control but costs more. (Key point: Comparison)

## Related in Building Technology

- [Passive solar design and building layout](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apassive-solar-design) — Building Technology, chapter 1
- [Achieving thermal comfort, active and passive methods](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aachieve-thermal-comfort-active-passive) — Building Technology, chapter 1
- [Renewable energy and trapping solar energy](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aenergy-renewable-solar-066j) — Building Technology, chapter 1

## Related in other subjects

- [Passive vs active replication; availability](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Apassive-vs-active-available) — Distributed System, chapter 7, asked 2×
- [Active vs passive; active replication working](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Aactive-passive-working) — Distributed System, chapter 7
- [Active vs passive; non-inverting (s+8)/(s+2)](https://www.bctengineer.com/question.md?key=semester_5%2Ffilter_design%3Aactive-passive-difference-noninverting) — Filter Design, chapter 6, asked 5×
- [Active vs passive; realize 4(s+2)/(s+1)](https://www.bctengineer.com/question.md?key=semester_5%2Ffilter_design%3Aactive-passive-noninverting-4s-plus-2) — Filter Design, chapter 6, asked 5×