What is renewable cooling?

Demand for cooling is expected to increase. Since most of cooling is using the electric compression cycle, this will result in higher demand for electricity and increased stress for the electric grid.

But this is not an unavoidable outcome. It could also very well be, that an increased cooling demand is not problem at all - if met by devices following the highest efficiency standards and using renewable energy in short, but efficient, renewable cooling.

And this term triggered me to write this short article, as I am struggling with it.

"Renewable Cooling". The 2009 version of the Directive on the promotion of the use of energy from renewable sources (2009/28) mentions cooling 52 times, without defining what renewable cooling should be. Since 2013, we have an agreed upon procedure on how to count the renewable energy contribution of heat pumps for heating, and again, no definition or accounting method for cooling was mentioned. Is cooling so difficult to understand? I guess not, as all of us have a fridge and understand what it does.

The "Renewable" in Renewable cooling makes it more complex. Let me try to explain why. 1. In renewable heating, the renewable share is the useful energy provided minus any energy needed to operate the process. For heat pumps, this means the drive energy is deducted from the useful heat - the remainder is renewable heat and the renewable energy is supplied in endless amounts outside the building. As the energy providing the evaporation effect is taken from inside the compartment (building/process) that is intended to be cooled, this energy is not renewable according to the definition (remember: renewable energy must come from the outside).

And then there is also a statistical issue: Traditional energy statistics is based on the trade of energy carriers. Only renewable energy, that is part of the energy market is metered. All other sources, in particular renewable heat, are deemed for statistical purposes. Doing so for cooling would be even more challenging.

2. Cooling is a service, derived from final energy - either via the vapor compression cycle or via ad/absorption. Rarely is cooling measured and if so, than the amounts are not transmitted to statistics authorities. A simplified approach to deem cooling provided via the number of units installed must fail, as the operating hours are not know and depend on comfort requirements, building standard, efficiency of the cooling technology and not least, the climate.

So what could be renewable cooling?

If you follow me insofar as to say that if it is renewable, then it should be replenished automatically, that could be a start.

A. Passive renewable cooling is the use of a naturally occurring and stable temperature difference

This means using the difference in temperature between an object to be cooled (for example a cookie) and another, cooler medium (for example air). So if I was a baker with the need to cool down my cookies after taking them from the oven, I could simple put them on the tray and expose that tray to the air around it. Voila: tasty cookies, cooled by a natural, free, renewable cooling process.

The same should be true for opening the windows in my house, office or factory or putting a few bottles of beer/soda/... or my body into cold water (see the picture above).

Examples with a bigger impact are the use of snow for cooling (as done in a hospital in Sundsvall), the use of ice (as done in the Hungarian Parliament building in Budapest) or the use of larger bodies of water via district heating systems.

From a heat pump perspective in geothermal and hydrothermal applications, the ground or the body of water can be used to cool the building or process. This application is in principle available for about 1 million installed units, pending a proper hydraulic set-up.

Trying to quantify: the given examples can be used to provide significant accounts of cooling, albeit a statistical approach, which could be similar to the one applied to determine renewable heating, needs to be developed .

B. Active renewable cooling is the result of a technological process

Technology to produce cooling/refrigeration most often uses a refrigerant cycle either run by thermal energy (sorption) or by mechanical energy (produced via gas or electric engines). The latter case is the dominant one and shall be explored here. It is important to get this right, as the technology based solution is providing most of the cooling today.

The cooling effect derived from the refrigerant cycle can be determined in the same way as renewable heating is determined: the amount of driving energy is deducted from the useful cooling provided. As the energy to drive this process comes from the inside of a building or from an industrial process (as cooling them is the goal of the exercise), the result is not called renewable cooling. Nonetheless, using this excess/exhaust or waste energy makes for a very efficient process.

Two attempts are made to determine renewable cooling from cooling/refrigeration devices

a) using the excess cooling (= waste energy) from a heating process, which is produced anyhow, without any further energy input. This cooling effect will happen automatically and the effect needs to be disseminated in order to close the cycle - so why not use it and benefit from it? I like the approach, but have to admit, that statistically, it will be a real challenge.

b) using 100% renewable drive energy. In this case, the drive energy is renewable, but depending on whether it is electricity or thermal energy, it is already counted in other parts of energy statistics and if a separate recognition of renewable cooling is wanted (and double counting is to be avoided), must be deducted from these statistical buckets.

This leaves me with some conclusions:

1. The current set of definitions and the systematic of statistics are not fit for recognizing the amount of energy used for cooling. In order to maintain the integrity of the system, the full amount of cooling can never be considered renewable with the current set of definitions.
2. At the same time, demand for cooling is expected to increase and efficient solutions exist in the combination of renewable drive energy (mostly electricity, but also thermal energy), the use of waste energy and the setting of minimum energy performance standards (MEPS)
3. The topic is of an importance, that should not be slowed down by the question of whether or not cooling is renewable. That's a challenge to policy makers, that is not addressed in the revised renewable energy directive.

The considerations presented here are very preliminary - I would like to know your opinion - do you agree, do you disagree, do you have a totally different opinion? (and please indicate where you come from, as your background and geographical location will most likely determine part of your answer).

The discussion is only beginning - so it will make sense to develop a good understanding with a wide range of stakeholders.

Version 1.1 - 25.8.2018

Version 1.2 - 30.8.2018: Added some examples for passive cooling that show, that this is already and established technology.