Getting realistic about what our historic buildings can be used for
Principal Engineer, Partner, Max Fordham LLP
The preservation of our historic building stock is crucial in our efforts to achieve net zero. When coupled with suitable heating technology, a properly maintained and draft-proofed historic building can be energy-efficient and comfortable. However, some buildings may have limitations on how much they can be changed due to their age or historical value, which can limit the extent of alterations. In such cases, it may be challenging to draft-proof these buildings to the required standards, resulting in higher energy consumption for maintaining comfort levels. One may question if an over-reliance on cheap fossil fuels has led us to use these buildings in ways we shouldn't.
As we look to a net zero carbon future, should energy use be the driver that dictates what a building could be used for?
The business-as-usual case typically looks something like this: the decision that makes the most significant contribution to energy use is when the client sets the brief, which dictates how the building will be used. The architect then decides what fabric improvements are possible within the bounds of conservation. We do not define minimum insulation levels and air tightness when refurbishing historic buildings, in order to avoid damaging historical or traditional building fabric. Upgrades are only encouraged if reasonably practicable, resulting in significant energy efficiency variation across buildings.
The heating system designer goes to work. Firstly, they determine what air temperature will provide comfort for the given activity as defined by the client's brief. Then, the heating system is designed to deliver the heat necessary to achieve comfort. It is not always possible to achieve the required level of comfort, regardless of the heat thrown at a space by the heating system.
Cold drafts are an issue in any building and will quickly chill anyone who cannot escape them. But with a large enough and hot enough radiator, most spaces can be made comfortable for almost any activity.
Heat pumps will play a key role in electrifying heating in a way that responsibly uses our available zero-carbon energy. A heat pump coupled with a low-temperature heating system will achieve the highest efficiency and lowest running costs. However, a low-temperature heating system is unlikely to be able to economically deliver the same amount of heat as a fossil fuel system due to the costs of large radiators, the heat pump itself, and possible electrical infrastructure upgrades.
This sounds like a problem for the deployment of heat pumps. Or perhaps we could see it as an encouragement to consider appropriate energy use? Just because we could make a space comfortable by throwing energy at it doesn’t mean we should.
Let us look at the design process again; this time, we bring energy use to the front and centre by setting an energy budget.
The architect makes the first pass at estimating what fabric energy improvements can be made while respecting the building's heritage and available budget. The heating system designer then calculates the temperatures that can be achieved within the energy budget.
The client can then decide if the activity they have planned for the space can be carried out comfortably. For example, if a person is shopping with a coat on, a space temperature of 16°C will provide comfort, but 22°C will be more appropriate for a restaurant where you will be sitting still and dressed to impress. If comfort cannot be provided within the limits of the energy budget, the client has two choices. Improve the fabric performance to a point where the space becomes viable for the chosen activity, or rethink what the space will be used for.