De-mystifying the low-carbon heat puzzle

De-mystifying the low-carbon heat puzzle

Chris Davis of Hysopt explains how HVAC digital twins are helping university energy and estate managers to identify optimum solutions for decarbonizing their heat infrastructure amid concerns over energy consumption and dependence on fossil fuels.

Against a widening backdrop of declared climate emergency, there is increasing pressure on university energy managers and estates directors to develop strategies aimed at reducing carbon emissions. In the UK, there is a target of ‘net zero carbon’ by 2050 to end our contribution to global warming. Universities are setting ambitious targets well ahead of the 2050 deadline and my company spoke to one energy manager recently who is aiming at 2030!

Many ‘low regrets’ options (where investment levels are moderate and there are no hard choices in terms of other objectives) have already being tackled, with lighting upgrades being an obvious example. Ongoing decarbonization of the electricity grid means reducing carbon from power is now reasonably straightforward.

Sterner challenges

Heat (and cooling) however represent more complex and costly issues with a myriad of technological solutions and integration options. Increasingly, universities have already adopted CHP (combined heat and power) as an energy-efficiency measure. CHP produces electricity as a useful by-product of heat generation so, in a time when both electricity costs and carbon emissions were high, CHP made sense and was a win-win option.

However, while electricity costs remain comparatively high (compared with gas), carbon emissions associated with electricity imported from the grid have fallen more than 50% in the last few years as a result of a changing electricity generation mix (virtually no coal, less gas and lots more renewables such as wind and solar.) This gives energy managers a dilemma because the lowest operating cost option for CHP no longer delivers carbon savings, meaning that universities must look at other solutions as part of their long-term energy strategy.

Cost vs carbon is increasingly going to become a trade-off where the lowest carbon forms of heat (and cooling) are not necessarily the lowest cost options. Meanwhile, electrification of heat (via technologies such as heat pumps) or development of heat networks connected to low-carbon energy sources (such as heat from waste) offer opportunities for campuses to really address the decarbonization of heat.

With complexity comes sensitivity

An area that is however increasingly misunderstood is correct hydraulic design, integration and control of these technologies, especially when dealing with complex installations. Lowering operating temperatures for example is something that needs to be thought about at the design and planning stage; it’s not a case of replacing gas boilers with heat pumps. Even with established technologies, such as CHP, it’s common for the hydraulic design and control strategy of the installation to mean that the CHP operates sub-optimally.  Hysopt has worked on more than 30 projects to optimize existing CHP installations where the hydraulic configuration of the system has been improved to increase thermal (and subsequently electrical) yield from existing installations,  resulting in 30-50% reductions in annual energy costs.

It’s also a given that as heating and cooling systems become increasingly complex, and with the addition of multiple heat sources, systems are becoming more sensitive to correct hydraulic design and control strategy.

Using digital twins to make the right decisions

Digital twins are not a new concept but it is only recently, with growing digitization and the advent of the Internet of Things (IoT), that the technology has gained traction. So, what is a digital twin? It is essentially a virtual replica of a physical system; in this case an entire HVAC installation or indeed an entire heat network (multiple buildings or campuses supplied by a single energy centre).

An HVAC digital twin uses the fundamental laws of physics to understand how a design performs. It can therefore be used to simulate how a design or system will behave in the ‘real world. This has significant benefits for university campuses looking to grasp how multiple and complex technology solutions across many buildings, each with their own heat demands, occupancy profiles and heat distribution technologies are likely to perform and deliver when measured against low energy, low carbon objectives. In short, a digital model of an HVAC installation gives energy managers and building owners real insight as to how their system works and allows objective comparisons between the impacts of multiple future design options. In this way, digital twins can help organizations to make the right technical and financial investment decisions, reduce risk and increase the prospects of delivering against targets by objectively quantifying ‘performance’ at the design stage.

Quantifying performance

Energy consumption, CO2 emissions and investment costs should be as low as possible in an HVAC design and at the same time, thermal comfort needs to be as high as possible. A digital twin that provides dynamic simulations of system performance allows multiple conceptual design options to be objectively compared against a range of key performance indicators (KPIs) such as annual energy consumption, energy cost, carbon emissions, comfort levels and capital investment. 

Sensitivity analysis (automatically performed by the digital twin modelling software) allows the preferred conceptual design to be refined in order to be fully optimized to deliver against the university’s prioritized objectives such as capital cost vs carbon emissions vs energy cost. The digital twin provides designers with an engineering tool that encourages innovation while their clients get full transparency over what they can expect before they make an investment decision.

Closing the performance gap

HVAC digital twins also perform another vital role which is to close the so-called ‘performance gap’ between design and as-built installation. How is this achieved? By using iterative optimization algorithms for selection of hydraulic components (pumps, valves, pipe sizing, heat exchangers, etc). Crude guesswork, ‘rule of thumb’ and the unnecessary addition of safety margins associated with traditional HVAC design practices are all removed, producing the additional benefit of helping to reduce upfront capital investment costs by as much as 10% on a new system installation. Furthermore, not only are these components correctly-sized and selected, the digital model also provides installers and engineers with information about how to correctly configure every component at the commissioning phase so reducing hours on site, removing ‘trial and error’ and helping to ensure the as-built design accurately reflects the optimized as-designed system.

Case study: Free University of Brussels

The Vrije Universiteit Brussel (VUB) has three different campuses: Etterbeek, Jette and Gooik. It also has various other buildings spread across the capital, and the hydraulic systems in all these buildings needed optimizing.

“The main advantage of a Hysopt digital twin,” says Eric Noels, Technology Expert Advisor to the university, “is that we now have a central platform where we can implement all the calculations for our complex heating system. Another benefit of the software is that it allows us to share models with partners as well as internally with our own departments.”

He continued: “Our heating system was originally designed for a high-temperature regime but the Paris Climate Agreement meant we had to reduce this. Unfortunately, it was virtually impossible to switch from the overheated network to a heating system with a lower temperature using traditional calculation methods. But thankfully, the Hysopt digital twin was able to resolve this problem for us. One of its most important features is the simulations which have enabled us to work out and refine the best design.”

VUB invested €600,000 to optimize the heating system, but according to Mr Noels: “Now we’re saving €300,000 a year which equates to a payback period of two years. We want to continue developing our heating system further in the future and use the Hysopt software for all our upcoming projects.”

With increasing technical complexity and growing pressure to reduce the environmental impact of campus buildings, HVAC digital twins bring transparency of performance at the design stage so allowing universities to make optimum engineering and investment choices that reduce costs and risk.

Rapid return on investment

The value a digital twin will deliver can be considered cost-neutral as annual energy savings and/or capital investment savings delivered from the digital model mean that any costs associated with production of the digital twin are recovered quickly. (Seventy-five percent of Hysopt projects pay back in under three years while capex savings on new installations more than cover the cost on day one.)

A digital model can follow the design process right through to installation and commissioning, evolving with the installation throughout its lifecycle.  The ability of a digital twin to empower and inform designers about future upgrades and extensions means that the approach should be considered by all innovative and responsible university estates.

Want to know more?  Hysopt’s HVAC digital twin software was recently awarded Product Innovation of the Year by the Chartered Institute of Building Services Engineers (CIBSE) at the 2020 Building Performance Awards. Judges commented on the scalability, breadth of applications and potential to link to thermal modelling tools. To date, it has been used to identify energy savings in more than 130 HVAC installations and, on average, found annual energy costs savings of 32%.