The Passivhaus Standard delivers radically energy efficient buildings with excellent occupant comfort. I have written about the comfort aspects of passivhaus before in the Gary Vaynerchuk inspired post and in one of the LovePH series.
Heating is a key element of occupant comfort. So why does the Passivhaus Standard have a limiting benchmark for heating energy of 15kWh/m2 per annum? Isn’t this contradictory?
While this may seem contradictory, there are good reasons for it. Firstly, heating makes up a significant proportion of energy consumption in buildings, so it needs to be addressed to improve energy efficiency and reduce climate change impact. Secondly, setting a very low heating energy benchmark drives a fabric first approach, which has several benefits, comfort being a key one. And thirdly, having a heating energy benchmark singled out from primary energy means it can’t be achieved by offsetting with renewables or any other energy accounting cheats.
15kWh/m2 for comfort – delivered with radical energy efficiency, fabric first design and no cheating!
Heating: The First Target for Energy Efficiency
The exact proportion of energy consumed to heat buildings is actually quite difficult to pin down. Usually the source of energy used for heating, whether it is gas or electricity, is consumed for other purposes in addition to heating. However, most reports point to heating making up between 40% and 60% of domestic energy consumption. For non-domestic buildings, the proportion varies more and depends on the type and use of the building. In all cases though, the proportion of energy consumed for heating is close to or more than half of all energy consumed in buildings.
To make buildings more energy efficient and to address climate change, buildings need to use radically less energy for heating.
As the largest single use of energy in buildings, heating is clearly the first target when it comes to reducing building energy consumption.
Less Heating, Fabric-First
Heating energy consumption can be reduced to a certain degree with an efficient heating system. However, to reduce heating enough to meet the very low 15kWh/m2 pa required by the Passivhaus Standard, a fabric-first approach must be taken. Mediocre insulation levels and building fabric that isn’t airtight, even when combined with a highly efficient heating system, will not reach this benchmark. The need for heating must first be significantly reduced by high levels of insulation and airtight building fabric. Only then will an efficiency heating system meet the benchmark. This has three clear benefits.
The first benefit is occupant comfort.
A building that is highly insulated and airtight with high-performance windows and doors will be warm and comfortable throughout. Unpleasant draughts, radiant cold from windows, cold spots caused by thermal bridges and unhealthy condensation are all eliminated. The high-performance airtight fabric also enables balanced mechanical ventilation with heat recovery to operate effectively. This provides pre-warmed fresh air at low speed, again eliminating cold uncomfortable draughts.
The second benefit is robust and durable long-term building performance.
Poorly performing or inefficient heating equipment, such as a boiler, is likely to be upgraded or replaced several times during the lifetime of a building. Even building services currently considered highly efficient are likely to be superseded and upgraded in a matter of years as technology advances swiftly. In contrast, building fabric is very rarely upgraded over the lifetime of a building. The initial investment locks in the majority of the fabric performance for the lifetime of the building. Therefore, prioritising the fabric performance, as the Passivhaus Standard does, ensures that the building will inherently perform well for the lifetime of the building.
We also don’t know what changes or innovation in energy generation might come about in the future. Nor do we know what changes in occupancy or building use might come about in the future. High-performance building fabric will still be beneficial in either case though, enhancing the long-term durability and resilience of this approach.
The third benefit is the return on investment (ROI).
Not consuming energy in the first place is much cheaper than renewable energy generation or consuming energy more efficiently. So by driving a fabric first approach and ensuring less energy is used by design, the Passivhaus Standard provides the best bang for your buck. This is further reinforced by the robust and durable long-term performance a fabric first approach delivers, reducing maintenance and replacement costs.
A fabric first approach delivers comfort, robust long-term performance and the best return on investment.
Less Heating, No Cheating
Heating energy is specifically singled out in the Passivhaus Standard to ensure all the benefits of a fabric first approach mentioned above are delivered. This also ensures a genuine reduction in energy consumption is achieved. A heating energy benchmark can’t be offset or achieved through energy accounting cheats. What do I mean by cheats? Here are three cheats that are avoided by having a heating energy benchmark:
Cheat 1: Delivered Energy
If the benchmark was for delivered energy (that is, the amount of energy delivered to the building) then it would be possible to meet the target through different means but with poorer performing fabric. For example, a building with poorer performing fabric could be heated using a heat pump that only consumed 15kWh/m2 pa (delivered) energy. However, with a COP (Coefficient of Performance) of 3, it could provide 45kWh/m2 of heating energy and potentially a good degree of comfort. While this kind of energy account cheat doesn’t seem like a huge difference, the result is that all the benefits of the fabric first approach are compromised. Furthermore, if at any point the heat pump doesn’t work, doesn’t reach a COP of 3, or gets replaced by a different heating source, then either energy performance is compromised as more heating energy is used, or comfort is compromised.
Cheat 2: Just Primary Energy
A similar approach could be taken if the benchmark was just for primary energy without singling out the heating energy portion. Lower fabric performance coupled with on-site renewable energy generation (or heat pumps) could possibly meet the primary energy target. This is due to the reduction in losses from energy generation and distribution that on-site renewables promise. This is an energy accounting cheat though, as the actually amount of energy being consumed is the same or even greater, it’s just notionally ‘offset’ at certain points in time. As I have written about before, relying on on-site renewable generation to reduce energy consumption is a flawed approach and can even lead to the opposite result. The effect of this, however the numbers add up, is that more energy would need to be consumed for heating to maintain the same internal comfort. And again, the benefits of a fabric first approach mentioned above would be compromised.
Cheat 3: Carbon Emissions
Measuring carbon emissions divorced from heating energy is just as problematic as the previous two cheats. A poorly performing building that is supplied in part by on-site renewable energy generation, or heat pumps, or biomass, can appear to have relatively lower CO2 emissions. As already mentioned, I’ve written about the issues with this ‘Zero-Carbon’ approach before. Aside from the big question of whether or not reduced CO2 emissions (and reduced energy consumption) are genuinely delivered by these means, there is no direct relationship to occupant comfort. And once again, clearly the benefits of a fabric first approach mentioned above would be compromised.
Having a heating energy benchmark prevents these energy accounting cheats. It ensures genuine reductions in energy consumption and high levels of comfort are delivered.
Less Heating, More Comfort
The Passivhaus Standard sets a very stringent heating energy benchmark of 15kWh/m2. This ensures that the main area where energy is consumed in buildings is addressed head-on. This is part of the reason why passivhaus buildings are so energy efficient with very low CO2 emissions by design. And this is what we need in the face of climate change.
And yet energy efficiency must not compromise occupant comfort. Otherwise we could just save energy by switching off and unplugging everything!
The heating energy benchmark ensures that passivhaus buildings must be designed with a fabric-first approach. The architecture must do the work delivering radical energy efficiency. The fabric-first approach provides excellent occupant comfort, along with robust and durable long-term performance and the best return on investment.
Singling out the heating energy from the overall primary energy prevents any energy accounting cheating. Genuine radical energy efficiency without a performance gap is the result.
It’s not just about heating energy though, the primary energy benchmark of 120kWh/m2 pa is still important. This compliments the heating energy benchmark by requiring passivhaus buildings to have efficient sources of energy, efficient appliances and equipment, efficient building services and efficient lighting.
The world needs buildings that use radically less energy and provide excellent occupant comfort. The Passivhaus Standard ensures this through a stringent heating energy benchmark. Less heating, better preforming architecture, more comfort.
Heat pumps were mentioned a few times in this blog post. If you want to learn more about heat pumps I recommend John Cantor’s excellent “completely hype-free” website.
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