1st August 2020
  •  
  •  

Ambient loop technologies and carbon zero

Introduction

Though global meetings aimed at galvanising world governments into climate change action, make steady but sometimes laboured progress, there can be no doubt that general awareness of climate change has never been higher. New laws and regulations resulting from governmental actions intended to reduce energy use and achieve zero carbon emissions have created a new market for emerging technologies that offer even greater energy efficiencies. Especially technologies for the next generation of highly efficient heating systems powered by electricity.
At an industry level, few industries have yet to consider practical steps to meet the effects of climate change on their sectors. This includes the construction sector.

What the data says

Current data helps us to understand carbon emission trends and how energy demand is changing. Specifically, the evidence points to a pronounced decrease in carbon emissions from grid electricity. This is pretty much the result of the systematic decarbonisation of power is the UK grid.

  • Since 1990, power station emissions (of carbon) have plunged by over 60%.
  • Extrapolations by The Department for Business, Energy, and Industrial Strategy (BEIS) predict an 80% plunge in carbon emissions from the most significant power companies, between 2010-2020.
  • Over the same period, UK electricity rose from 22% to 65%.
    On a slightly more technical level, estimations for emissions intensities relating to grid electricity by the year 2035 are calculated to be 41gCO2e/kWh. This is well below BEIS’s 2017 projections of 55gCO2e/kW. Great news. But what caused this abrupt downturn? Answers can be found in the data.
  • In 2010, the amount of power derived from fossil fuels was equivalent to 288TWh—75% of the UK total.
  • Renewables in the same timeframe was equivalent to 26TWh—a tenth of the fossil figure. (Source: Carbon Brief, 2019.)
  • United Kingdom electricity generation measured in 2018 showed the lowest levels in a quarter of a century–335TWh.
  • Renewable source data demonstrated that another record had been broken, with an estimated 33% of the UK total in 2018.

From a climate perspective, it is definite that in the United Kingdom, continued prosperity no longer requires an increase in electricity use to power economic growth. If we measure the per capita use of electricity since 2005, we find a 25% drop. This is the lowest level in over three decades. It is encouraging indeed.
In other words, the UK economy has doubled since 1980, without a concomitant growth in electricity demand.
Why is this? Although it’s supposition, the cost of power and austerity are likely factors. What’s sure is that there has been a steady, large-scale decline in UK manufacturing as service industries gained a foothold and expanded.
On a positive note, on the regulatory front, more stringent regulations governing consumer products’ efficiency, the wide-scale introduction of highly efficient lighting, and the change to more effective consumer appliances to replace older, less environmentally friendly devices as consumers become far more ecologically aware.

Where to now?

In a domestic and industrial near-future featuring declining emissions, technologies focused on renewables, and the continued development of nuclear power will increase market share as fossil fuels are displaced.
The future is indeed bright. Projections indicate that carbon emissions relating to electric power generation will trend steadily downwards over the next decade and a half. Of those countries on the vanguard of tackling climate change, Scotland offers a shining example of what might be achieved, with three-quarters of electricity coming from renewable sources (2018 figures). By 2020 it is predicted to reach 100%.

Opportunity knocks

These factors have driven revisions of planning strategies and building regulations to take account of tumbling emission predictions. Importantly, these changes offer huge commercial prospects for modern electric heating systems, precisely because of their increased capacity for lower emissions.
What will electrical heating systems look like in the future?
The acronym, SAP, stands for Standard Assessment Procedure for Energy Rating of Dwellings. Hardwired into the SAP calculations (2012 version) is an assumption that electricity produces just under 2.5 times the amount of carbon emission as that of mains gas. Such an assumption is inaccurate, based on historical carbon factors that fail to consider a critical fact: that the current grid energy mix contains a growing proportion of clean, renewable energy.
Viewed from an SAP 10 perspective, based on both contemporary and projected data, electricity-related emissions have fallen from 0.519kg CO2/kWh to 0.233kgCO2/kWh. This represents a considerable reduction of over fifty per cent. From this point of view, electricity emissions are slightly above those of mains gas. Nor does this downward trend stop there. SAP 10.1 sets its sights even more ambitiously on a reduction to 0.136kgCO2/kWh. This would make electricity significantly more effective in emission reduction than gas.

Distribution loss

Yet lower emissions from electric powered forms of heating aren’t the only reason; new power initiatives outflank gas boiler and CHP systems. Gas and CHP energy systems exhibit comparatively higher distribution losses. This is a scientific fact, demonstrated whenever hot water is used as a means to distribute heat.
BRE’s 2016 report took as its subject matter, distribution loss factors in heat networks for homes. The study suggested significantly higher distribution losses than SAP 2012’s figure of 1.05—a figure traditionally used to derive distribution losses between a building’s plant room and the point of use.
Once 12 months of data had been amassed, it became clear that the lower an apartment’s heat load, the higher were distribution losses expressed as a % of the overall load. Consequentially, the current base value of 1.05 was raised to 1.5. This is equivalent to a 33% loss—close to a seven-fold increase. Systems designed in line with CIBSE/ADE Heat Networks: Code of Practice for the UK, display a default value of 2—equivalent to a 50% loss.
Distribution loss factors matter because of efficiency. But there is a ‘comfort’ dimension too. Heat loss from distribution conduits in thermally efficient buildings can increase air temperatures, unhelpfully overheating risers, passageways, and rooms. In some cases, this heightens the need to ventilate. And if this doesn’t do the trick, mechanical cooling maybe needs to achieve optimum conditions. Such mitigation inevitably equates to higher bills and a less than effective building.
Although the longer-term aim is to connect to a district heating system, the preferred choice is for communal infrastructure based on heat pumps when choosing a common heating source. This type of system can be readily hooked up to a district heating system in the future. This strategy offers many opportunities to develop heat pump technology.
Heat pumps work on electricity—a key differentiator in this market because electricity is clean at the point when consumers use it. By comparison, burning gas generates toxic waste products such as nitrous oxide, necessitating flues, which simply adds to costs. And given that new regulations call for stricter regulation of air quality in new developments, it will become mandatory for companies applying for local authority permits for gas CHP, or boiler-based systems, to determine how they intend to minimise any impacts their technologies may have on air quality.

Planning policies

The Greater London Authority’s (GLA) 2017 plan (draft) adopted a different approach whose goals include:

  • Less up-front energy consumption
  • More effective home insulation
  • The ‘clean and efficient supply of energy,’ whatever the system used
  • Renewable energy in all new housing developments. This would achieve carbon emission reductions of 35% above Building Regulations requirements.

As a follow up to the 2017 draft plan, the GLA published an Energy Assessment Guidance document, urging energy assessors to employ SAP 10 carbon emission data for all new developments. Due to heat pump efficiency, gas boilers are likely to be phased out.
A tariff of £60 per tonne of carbon emissions per year (for 30 years) will be levied as a commercial incentive. The latest draft London Plan is likely to recommend an increase to £95 per tonne. These guidelines apply to London only, though it is thought possible that regional authorities will soon follow suit.

Heat pump solutions

It would be useful to now review how heat pumps work. In simple terms, heat pump solutions move heat around. The heat has to be moved from within the building to outside the building. The reverse is true when heating. Heat pumps achieve this through something called the vapour compression cycle, which employs a refrigerant.
Throughout the cycle, changes in pressure govern the refrigerant’s physical properties to either absorb or discard energy in the form of heat. Coolant transiting an expansion valve loses temperature and pressure.
Thus cooled, the refrigerant enters a heat exchanger. Within air-source heat pumps, the heat exchanger takes a coil housed in the unit outside. Air passing over the coil, transfers its heat to the very low-temperature refrigerant, causing the refrigerant to evaporate. Heated refrigerant vapour now moves to a compressor. Here, it rejects its heat across a 2nd heat exchanger, aka a condenser. As the refrigerant’s heat is expelled, the refrigerant condenses. The resultant liquid, now cooled, may now be used to run the cycle over again.
Heat pump efficiency is measured as an energy efficiency ratio (EER). This is calculated as the heat absorption ratio absorbed by the pump divided by the energy the heat pump uses. Discussions about heating efficiency use the term “coefficient of performance” (COP). This is the ratio of heat rejected divided by power input. This rejected heat is always the sum of the absorbed heat plus the power input. Basic maths help us demonstrate that heating outputs and efficiencies are higher than cooling.

Measurement

Measures such as EER and COP are critical if we understand the energy efficiency of heat pumps. And also what this energy-efficiency tells us about carbon emissions and energy consumption. With the introduction of the Energy Related Products Regulations, the efficiency in cooling and heating of a heat pump system has changed to seasonal efficiency, which considers system performance throughout the year – as represented in SEER and SCOP.
This is not the place to carefully follow the derivation of such calculation. Suffice to say that the change’s primary effect is to gain a better insight into system performance throughout the year and the changes in external temperature that occur.
We can use this calculation to derive the carbon emissions from electricity consumed by the heat pump, which involves the multiplication of an energy consumption figure by a carbon emission factor (CEF). The primary energy factor (PEF) links primary to final energy by determining the amount of primary energy required to generate one electricity unit. Significantly, fundamental energy measurement is set to become the basis for compliance under new Part L guidance.

Performance and compliance

In the meantime, the yardstick for compliance remains carbon. Independent studies show the impact of the change in the carbon emission factor. If we use the former carbon emission factor of 0.519kgCO2/kWh, CHP systems just meet carbon reduction targets, but only when used in residential blocks consisting of over seventy units, or in hotels with around one hundred rooms. On the other hand, heat pump systems fail to meet the standards required.
However, considering how heat pumps work and using an SAP 10 carbon emissions factor of 0.233kgCO2/kWh, it can be demonstrated that heat pump systems are more than capable of achieving carbon reduction targets. CHP systems, communal boilers, and direct electrical systems need additional carbon reduction measures to make the 35% carbon reduction target.
Using up-to-date SAP 10.1 figure of 0.136kgCO2/kWh, the difference will be even higher. So while historically, planning sought to prefer combined heat and power systems in medium to large scale residential projects, the suggestion is that, in the future, new policies may wipe out any advantage CHP once had. Where carbon reductions of around 35% become the intended target, at least in residential developments, the default solution becomes the heat pump.

Ambient loops

And so, to ambient loop systems. These work by circulating low-grade heat to every dwelling in a development. Each apartment houses a water-to-water heat pump that draws water from the ambient loop, raising its temperature to a suitable heating or hot water level. Heat pumps in apartments function quite effectively when loop temperatures are maintained within quite broad parameters (between -10°C and +30°C.)
The ambient loop concept brings several heat sources within its scope, including:

  • ASHP (Air source heat pumps)
  • Boreholes with thermal piles
  • Surface water such as a sea, river or canal
  • A fourth or fifth generation district heating
  • Waste heat recovery.

We discussed above the recurring problem of overheating in high-temperature solutions. In an ambient loop system, moving low-temperature heat from site to site can be achieved with negligible heat loss. As a bonus, apartment heat pumps can generate cold water for cooling.
Another positive commercial aspect of ambient loop systems is that the same plant and pipework is used for both heating and cooling—no additional costs. Apartment heat pumps simply work in reverse, absorbing energy from the loop instead of discarding it. Considerable savings can be made by having a single, dual-purpose central plant heating system instead of two separate systems.
Heat pump efficiency varies according to the source temperature:

  • Shared borehole array: 10°C average to the heat pump = COP of 6 for heating; 35°C for underfloor heating, and 3.2 for domestic hot water (at 55°C). There are similar efficiencies for surface water.
  • Ambient loops pre-heated centrally by the heat pump to 25°C, a COP of 11.2 in heating (at 35°C for underfloor heating), or 5.7 for domestic hot water (at 55°C). This can achieve seasonal efficiencies of between 3 and 3.2. The point of optimal efficiency for a primary loop is 25°C.

Apartment heat pumps connect with the loop. For domestic or hot water heating, the heat pump draws water out of the loop before heating it between 35°C and 60°C (user’s preference). Economies of scale can be achieved in larger complexes through the use of centrally located heat pumps.

An example of typical carbon reduction

Results from an SAP-based calculation to compare an ambient loop system with a combi central boiler/CHP system are revealing. Assessments were made using SAP 2012 with adjustments to consider changes in carbon factor and distribution losses under SAP 10.

Results

No discernible difference could be seen using Elmhurst’s Design SAP 2012—it didn’t appear to drive change. Switching to a SAP 10 perspective made a big difference. There was a marked reduction in the calculated dwelling emission ratio for the ambient loop system. Also, the dwelling emission ratio for the boiler/CHP system significantly increased. Over the whole block, comparing a current CHP/boiler system with a future ambient loop heat pump system generates CO2 savings of 143 tonnes.
Framing this reduction in carbon reduction in terms of reduced offset payments makes ambient loop heat system technology compelling.

Chris Nicholls
Commercial Director

Read More