Design question examples - Systems

A design question is a way of stating an issue or query in such a way as to produce information on which a design decision can be made. These are example design questions pertaining to building systems.

MC Building Physics can answer these types of questions using a number of methods depending on your requirements.

Can solar thermal be combined with a building's existing systems?

Why investigate the feature?

Solar thermal water heating uses solar energy to heat domestic hot water.

Hence either designing in or retrofitting solar water heating panels could achieve savings for hot water production.

What are the issues?

When the hot water is required.
How much hot water is required.
How much solar heating is available.
When the solar heating is available.
Is it more effective to fit photovoltaic panels instead?
Health and safety
What the conventional hot water system is.

What are the criteria for adoption?

Possible criteria are -:

Financial - Simple payback, NPV
Carbon emissions reduction - Tonnes saved, cost per tonne saved.

Break the issues down

Estimate when and how much hot water is needed. Options include (in ascending order of complexity) -:

Using benchmarks or guidance figures.
From metered data in an existing building (if available).
Temporary installation of instrumentation to measure demand.

Estimate when and how much solar heating is available. Options include (in ascending order of complexity) -:

Using benchmarks or guidance figures.
Calculation of available solar from weather data files.

Evaluate how much use can be made of the available solar heating. Options for this include -:

Rule of thumb or hand calculation.
Spreadsheet calculation.
Full simulation of the solar thermal system.

Will chilled beams work in my building?

Why investigate the feature?

Using chilled beams are an inherently efficient way of providing cooling in a space.

If comfort cooling is deemed necessary then this method will be a high performance way of supplying it.

What are the issues?

Amount of cooling required.
Space for the beams.
Type of chilled system (ceiling, passive or active)
Fresh air supply method.
Chilled water temperatures used in the building.

What are the criteria for adoption?

Sufficient capacity being installable
Financial - Simple payback, NPV
Carbon emissions reduction - Tonnes saved, cost per tonne saved.

Break the issues down

Calculate the amount of cooling required - This should only be done using the approved method (CIBSE in the UK).

Evaluate energy savings. Options include -:

Simple calculation based on cooling hours.
Full simulation of system.

Is mechanical ventilation with heat recovery a better choice than natural ventilation?

Why investigate the feature?

Both methods of ventilation have plus and minus points.

Which is better for the application is very dependent on the building design, how it is used and the climate.

What are the issues?

Fan energy versus recovered heat energy.
Control of ventilation.
Service space.
Cost (capital, running and maintenance).

What are the criteria for adoption?

Financial - Simple payback, NPV
Carbon emissions reduction - Tonnes saved, cost per tonne saved.
Occupant satisfaction/productivity

Break the issues down

Energy use - Calculating the comparative energy use between the two systems is the key part of answering the design question. Stage by stage it requires the following -:

Define how the building is to be used including occupancy, ventilation strategy.
Predict the energy use of the building for both cases.
Use the predicted energy use to evaluate the financial case for each.

Control of ventilation - The following need to be considered

Supplying sufficient fresh air.
Ventilation to prevent overheating.
Night purge cooling.