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CHP for residential care homes (Combined Heat and Power).

The Cogeneration Gap – Part 1

Often seen as an ideal application within the residential care home, in this short blog series Adveco discusses the argument for onsite energy cogeneration, the operational costs, the environmental impact and highlights the increasing performance gap between ‘dirty CHP’ and the latest generation of highly efficient micro-CHP…

Whether building a new residential care home or refurbishing an older property to be fit for purpose, the importance of energy provision has risen up the agenda, resulting in a proliferation of on-site power generation. According to a report by Centrica Business Solutions (The Energy Advantage Report, June 2018).

“…more than 80% of commercial operations are expected to invest in on-site power production to generate up to a quarter of their electricity requirements by 2025.”

One popular choice has been the deployment of combined heat and power (CHP), also known as cogeneration. This is the simultaneous production of usable heat and electricity from a single process and source of fuel (typically gas) and is one of the most effective methods available to significantly increase the energy efficiency of a building. With an engine directly coupled to a generator, similar levels of efficiency to that of a conventional source of power can be achieved, and by locating such an installation on-site at the point of consumption, the usual energy losses associated with power transmission through the grid are eliminated.

Additionally, thermal energy is extracted from the CHP process by recovering the waste heat produced by the engine and generator during the power generation process. This drastically reduces the amount of fuel energy lost to the environment as exhaust, instead using it to contribute towards a local heat demand. With a significant continuous demand, such as would be typically seen in a residential care facility a CHP unit can run for very long periods of time and thus drastically reduce the reliance on conventional boiler technology and improve the overall efficiency of a building, reducing emissions and making financial savings.

Understanding the advantages of CHP

For operators and managers of care facilities, there are two basic questions to ask. If you have CHP what should you do with it? If you don’t, should you upgrade your plant room to include CHP?

I want to make it clear that in my opinion there are enough benefits that you definitely want CHP, but you may not want to buy it outright. CHP will have an environmental and cost savings impact in any building, but it only provides a payback case on Capex in the right type of building. That is why you may not want to invest in the technology.

If your building already has CHP it is because someone made the decision to select Combined Heat & Power based on either a financial or an environmental reason. But there are notable differences in between those who design, and those who operate the building.

Designers have historically chosen CHP based on carbon savings requirements from things such as Part L, or the London Plan, which other UK cities will mirror, rolling out their own equivalent local environmental policy.  Designers need carbon savings to get planning permission for a project to be built. It is the most important thing for the designer, and it is the minimum that must be done to successfully complete their job. That is why the designer selects CHP. If you inherited a building built in the last five years with CHP, then it was probably selected for SBEM carbon savings to meet Part L.

So, in this scenario you have CHP, but if it was installed purely for carbon savings, then we have to accept that may not be the most important thing to the end client and their facilities management team. Foremost is the functioning of the building, so the priority is the reliability of supply of heating and hot water, next is the operating costs of the building, and this is then followed by environmental concerns like NOₓ and carbon emissions.

It needs to be recognised that CHP is a support technology, as opposed to a critical technology. Water heaters and boilers are critical equipment, if they break down it influences the heat and hot water supply to the building, and therefore the comfort and safety of the residents. CHP, like many renewables, makes no difference to the reliability of the supply. Whether it is on or off the building still has heating and hot water. If you have inherited a CHP, then you need to decide what you want to do with it.

Shutting it down is an option. You could turn it off and forget about it.  If you do that then you will pay no maintenance, nothing for energy consumption by the unit and, there will be no loss of heat or hot water supply. You will not have any carbon savings either, but, since the building regulations are not policed you can, unfortunately, do this.

Alternatively, you can pay for maintenance and energy and then start reaping the rewards of operating the CHP. Rather than using just gas or electric water heaters for all the domestic hot water (DHW) needed for washing, cleaning, showers and baths, the CHP will supply heat captured from its operation to warm, or preheat stored water. The CHP can supply as much as 90% of the hot water needed by the care home with the water heaters used to ‘top-up’ the water temperatures and meet periods of high demand for Part L systems. CHP is also a great way to build a guarantee of consistent hot water service. Typically, a care home system will operate two or more water heaters, but should one fail it would result in a reduction in available hot water. With the addition of a CHP able to preheat at least 60% of a care home’s hot water needs, residents and staff should not see any obvious change in their hot water services should a water heater fail.

In part two we will consider the cost of operating CHP and gauging when and if you should look to upgrade to the technology…

Micro-CHP and The Urban Balancing Act.

Micro-CHP and The Urban Balancing Act

Adveco expert Bill Sinclair, Technical DirectorAdveco’s Technical Director, Bill Sinclair, discusses balancing concerns over the cost to health from NOX emissions with the advantages of using micro-CHP in urban commercial building projects.

A by-product of the combustion of hydrocarbon fuels, Nitrogen Oxides (NOX) are a major contributing factor to poor air quality, the most toxicologically significant being a combination of nitric oxide (NO) and nitrogen dioxide (NO₂). It can cause lung irritation and respiratory infections as well as being linked to cancer, asthma, strokes, and heart disease. The Royal College of Physicians believes it directly leads to as many as 40,000 deaths each year with an estimated cost of £20 billion to the country in healthcare and lost working days. This has led to widespread recognition that more needs to be done to address NOX emissions with attention more than ever-shifting to encompass the production of emissions from the built environment.

With a greater emphasis on renewables to make our cities more self-sufficient and resilient in terms of meeting energy needs, low carbon electricity’s share of generation has currently risen to a record 50.1% across the UK with (33.4% of which is generated by renewables). But, as old power plants go offline and are replaced by unpredictable supplies like solar and wind, combined heat and power (CHP) becomes increasingly advantageous. Able to reduce a building’s reliance on the grid, yet when demand is high such as when it is cold and dark, provide a more reliable power source, CHP also has the added benefit of providing high-grade heat at lower cost in conditions where a heat pump coefficient of performance falls and the energy cost increases beyond that of gas.

Although all CHP with a catalytic converter is cleaner than the grid, localised NOX emissions from ‘dirty’ cogeneration should be a concern. Where CHP is used to offset condensing boiler run hours, if the CHP is dirtier than the condensing boiler then the local emissions are worsened. Despite air pollution and NOX mainly arising from road traffic – half of the current NO­X pollution in London is attributed to vehicles – emissions from decentralised energy production are now being seen as a contributing factor. It is therefore of great importance that the NOX emissions from new CHP units within built-up areas are lower than condensing boilers if they are to have a positive effect.

Setting a new threshold for emissions

Micro-CHP (Combined Heat and Power) in urban commercial building projects.The 2018 EcoDesign directive sets a NOX emission limit for CHP units at 240mg/kWh. This threshold, despite being approximately equal to emissions that would result from producing heat from a boiler and consuming electricity from conventional power plants, is too lenient. Air quality has been a critical driver in the revisions within the London Plan which now treats CHP with a lot less enthusiasm – although still accepting that there remains a strategic case for CHP systems as long as the NOx emissions are equivalent or lower than those of ultra-low NOx gas boilers.

The cogeneration industry has not been sitting on its laurels, and a new generation of ‘clean’ CHP brings all the advantages of onsite, on-demand cogeneration, and exceeds the London Plan’s expectations of ‘very low levels’ of NOX, meeting Euro 6 standards for emissions. More compact and much cleaner, micro-CHP units (in accordance with EU standards at 50kW or less rated electrical power) are available with far lower emission rates. This is the case for the TOTEM m-CHP, for example, which is independently certified at just 10mg/kWh.

If we compare a CHP meeting the 2018 EcoDesign limit of 240mg/kWh to that of a TOTEM m-CHP, we can demonstrate the real difference in the latest generation of CHP. Using a unit of 20kW electrical output, a gas input of 70kW, in a situation with an average annual run time of 6,500 hours for a standard application such as a hotel or apartment block, the yearly NOX emission from a ’dirty’ CHP will be 109.2kg/year, compared to 4.55kg/year for Adveco’s TOTEM. And remember, this option is also improving local air quality because the m-CHP is used to offset the run hours of a condensing boiler which at emissions over 30 mg/kWh is dirty compared to the CHP.

Hybrid futures

There will always be projects where in certain circumstances m-CHP will have a place and other renewables are closed out due to limitations of either the site or the technology. By the same token, we would never advocate m-CHP for every building. As is so often the case in the commercial world, each project will have its specific requirements, requiring a more bespoke approach to the provision of hot water, heating and power generation.

Increasingly we hear from consultants who are struggling to pass any kind of gas or gas CHP based heating system because of the issues around NOₓ emissions, despite the advantage of the high-grade heat necessary to meet the needs of commercial projects. Simply opting for heat pumps, providing a lower grade of heat, isn’t a practical alternative. One answer then is to use a combination of two or three technologies to provide a high heat, low cost, low NOₓ system.

This is particularly relevant to large buildings where a heat pump alone is simply not suitable. These projects need an additional, high-grade source of heat. Now, that essentially takes you to gas, but if the building is big enough, after the heat pump, but before the gas, can sit m-CHP to provide low NOₓ and very low running costs.

We can also make a case for using Combined Heat and Power in existing buildings which already have gas boilers and do not have the electrical supply needed to utilise a heat pump. Again, it does not make sense to fit just a heat pump. But we do not want to use CHP to offset low-temperature heat pumps, it has to sit after a heat pump, offsetting the gas heater. Such an approach will still offer some carbon savings, definitely cost savings and, if that CHP is a low NOₓ appliance when compared to the boiler, then we also have NOₓ saving. At worst such a system is going to be carbon neutral, but cost and NOₓ effective.

The move towards all-electric in smaller buildings also reopens the door for solar thermal with better payback case and better carbon savings. Used in conjunction with low-temperature ASHPs in an arrangement to ensure that it offsets the high-grade source, it offers an alternate hybrid approach that does not require CHP. But we believe gas-fired m-CHP will continue to play a necessary role as part of many hybrid systems, achieving effective water temperatures for commercial applications whilst balancing running costs and savings.

As with any project, design what is best for the building. We would never advocate ignoring the risk of increasing air pollution locally with ‘dirty’ CHP systems, so if Combined Heat and Power is the best fit for your project’s needs then it is vital to choose the lowest NOX emitting equipment available. Right now, the Mayor of London is supporting the city’s Cleaner Heat Cashback scheme for SMEs, proposing scrapping of old gas boilers and replacing them with a variety of options including new efficient gas boilers. If we can demonstrate that m-CHP, either standalone or in a hybrid system, can offset condensing boiler run hours and make emissions cleaner then there is surely a place for the technology, even in the centre of our busiest cities.

Discover more about TOTEM m-CHP 

Download the TOTEM m-CHP brochure