Impuls3 – example Requirements Specification

Requirements Specification – Water cooker

 

ID: RS-WaCo-789
Revision: 07
Revision date: March 22, 2021
Revision status: released

Introduction

Electric water cooker

The System-of-Interest for this specification is a water cooker. The specification is intended for system-level requirements. The system (or product) is treated as a black box. In this specification the term system is used for the product. All requirements in this specification use the abbreviation WCS for Water Cooker System.

In the Requirements Analysis is stated that the main function of the WCS is “to bring water to the boil“.

Requirements are based on the ⌊Requirement template⌋.

Conditions

[CND-001] Normal operating conditions
The normal operating conditions for the product are:

  • temperature range: 5°C to 40°C
  • humidity range: 30% to 95%

 


Requirements

System-level main function: “bring water to the boil
Requirements in this section specify properties of the main function.

For all requirements condition [CND-001] applies.

REQ-001 boiling speed performance
The WCS shall bring 600 ml of water at room temperature to the boil within 3 minutes
Conditions [COND-001]
Sources [UC-789], [UC-876]
Status draft
Version, revision 3.14
REQ-002 electric energy resource
The WCS shall use no more than 100Wh to bring 600 ml of water at room temperature to the boil within 3 minutes
Conditions [COND-001]
Sources [UC-789], [UC-876], [analysis: electric energy]
Status draft
Version, revision 1.2

System-level secondary function: “maintain water temperature
Also called product features, Kunden erlebbaren Funktionen.

REQ-003 rotatable cooker body 
The WCS can be rotated on its base
Conditions [COND-001]
Sources [AS-001]
Status draft
Version, revision 1.2

Constraints, pre-conditions, standards

REQ-004 applicable standard: IEC 60335-1 
The WCS shall comply to the safety standards for household appliances IEC 60335-1 
Conditions [COND-001]
Sources [AS-002]
Status released
Version, revision 1.1


Annex A: Requirements Analysis

Stakeholder needs on “ease of use”

A number of stakeholder needs refer to ease of use as an important quality of the product. In this section the analysis is described how these stakeholder needs are interpreted.

Several models (also from competitors) show a base that includes the power cord, on which the kettle rest be positioned in any direction. Customers consider this feature to be very pleasant. Also considering some safety aspects: the kettle is automatically detached from the power source once it is lifted from the base.

AS-001 product can rotate on base
The feature that the water cooker can rotate 360° on the base / docking station / pedestal is considered to be important 
Stakeholder needs [UC-010] 
Status accepted
Version, revision 1.0

Applicable standards

AS-002 applicable standards

As stated in the marketing report MRKT-2021-4.2, the following standards apply to the product

  • IEC 60335-1 is part 1 of an international standard that addresses the general requirements for electrical/electronic household appliances and similar applications. The standard covers devices with rated voltages up to 250 V for single phase and up to 480 V for multi-phase.
References [MRKT-2021-4.2]
Status accepted
Version, revision 1.0

Electric energy consumption benchmark

How much does it cost to boil the kettle? (from: Canstarblue Australia)

Boiling an electric kettle costs 4 to 5 cents, depending on the size of the kettle and the rate you pay on electricity. Most commercial kettles range in size from 1.5L to 1.8L, with the larger kettles intuitively consuming more electricity. Kettle power will also vary between 2000W and 2400W, however this is much less important as you will soon see below.

To calculate the real running cost of a kettle, we must first work out how long a kettle will take to boil given its size and power. The below table assumes the kettle is filled to its maximum recommended capacity and the beginning water temperature is 20°C.

1.5L1.6L1.7L1.8L
2000W4m 12s4m 29s4m 46s5m 2s
2100W4m 0s4m 16s4m 32s4m 48s
2200W3m 49s4m 4s4m 19s4m 35s
2300W3m 39s3m 53s4m 8s4m 23s
2400W3m 30s3m 44s3m 58s4m 12s

The wattage of a kettle refers to how much energy it will consume within one hour. So a 2200W, for example, will consume 2200W in one hour (or 2200Wh/2.2kWh). However, as we calculated above, it only takes 3-5 minutes to boil a kettle, meaning it’s only consuming a fraction of electricity.

To elaborate, let’s take a 1.7L, 2200W kettle. When full, this kettle will take 4 minutes, 19 seconds to boil. In that period of time, the kettle will use 158.3Wh or 0.1583kWh of electricity. If you are charged 28.7c/kWh for electricity, then this means that boiling the kettle has just cost you 4.55c.