Chapter 1. Introduction

For the greenhouse project we’re planning to install a heat/cold storage underground. This is a plan that didn’t seem very feasible at first as the impression was that it would require major investments. This impression was based on lack of knowledge about the different functions.

When we want to heat a home with earth warmth, energy needs to be IN the ground first. Typically this could be the case when the sun heats the upper layer of the earth during daytime and this energy gets regained during nighttime. However, with a greenhouse things become a little easier; A greenhouse generates a lot of excess heat during a sunny day. We can store this excess heat underground as well, just like the sun warming up the ground would do under normal circumstances, and use this excess energy to:

  • heat the house during nighttime
  • heat fishwater during nighttime

Schematisch Overzicht

Section 1. Aardkorf

Aardkorf is the Dutch term for a great big tube basket underground. Basically it gets put underground only 4 meters deep while the height of the basket does not exceed approximately 2 meters. This is well under the frost line (20cm). Information from the vendor on how much this costs, we still see a pretty steep price:

  • approx. 650 euro/basket
  • approx. 250 euro/hole in the ground


Having approx. 3 of these baskets installed would therefore cost approx. 3000 euro. Far less than a vertical heat/cold storage but still a rather big expense.

So I tried figuring out what these are made of and it appears they’re about 100m of Tyleen, simply bundled together by 4 bracing pieces of wood. 100m of tyleen and some wood costs approx. 50 euro. Adding some t-and-right-angle connectors for the piping costs a couple of euros, renting an excavator from Boels in Almere costs approximately 200 euro and propylene glycol costs about 35 euro for a 10 liter jerrycan. Since the 300 meter of tube will contain approximately 160 liters of liquid, in order to protect it against freezing up to -11C we can dilute the  glycol approx. 25%, so we need 4 of these 10 liter jerrycans. This would total about 500 euro, a day or so to assemble the baskets and a day or so of digging with the excavator.

Section 2. Excavator

So I’m going to have to do a LOT of digging. I decided to rent an excavator from Boels.


This is a 1.5 ton excavator and according to the specs it will dig up to 2.30 meters deep. That’s pretty good as it is and it’s certainly going to make a HUGE difference compared to doing it with a shovel!! However, I will need to dig a ramp first and then drive into the ramp with the excavator so I can dig to 4 meters.

The day price for a machine like this is 175 euro and having it delivered and picked up will be another 50 euro, so this is the most expensive part of the heat/cold storage project. However it will be worth it as I’ve always wanted to use a tool like this. FWIW, Tracy has also indicated ‘Me too!’

Section 3. Propylene Glycol

The water that goes into the pipes needs antifreeze. We could of course simply buy some at the car shop but that’s pretty toxic stuff.

So we searched around and Tracy found this company that sells ‘biologically degradable antifreeze’. A quick scan indicates that the active ingredient is propylene glycol. So I searched for where I could find this and I guess it’s actually pretty safe as it gets sold as… cow food!


Got a nice discount on it as well!

Section 4. Tyleen

I also found a nice site which sells tyleen tubes at a very nice low price! Ordered 3 of these 100 meter rolls and some coupling pieces.

TyleenSet back another 135 euro, so it’s starting to add up.

Chapter 2. Permit

While ordering all this stuff I’m pretty much backing myself into a corner as I do not even know for sure yet if I’m allowed to do this or whether I need a permit to do so. If I need a permit, will I actually get it? Keep your fingers crossed for me please.

UPDATE: Well, I guess keeping your fingers crossed worked!! I just received a phone call from City Hall by a very friendly lady who had been forwarded my request about a permit. While she was on the phone with me she also received my greenhouse plan and was apparently interested enough to set up a meeting with her and the city’s ecologist!

UPDATE 14-01-2014: Sent another email to Duurzaam Almere to ask about the appointment but mostly about the permit and if I even need one. We’re planning to start digging in the backyard as it is all cleared up from trees and bushes now, the tyleen tubing has been delivered, the propylene glycol has been delivered, etc. We’re now also planning to  reuse rainwater. We’ll need to be digging for this as well so this can be combined nicely.

UPDATE 23-01-2014: Tracy and me had a very positive meeting with two people from the city of Almere, Anne Marie van Osch (Projectleader Sustainable Energy) en Roel Njio (Relationmanager VTH). The baskets don’t require a permit, but they need to be reported.

UPDATE 19-02-2014: A while ago I decided to send an email to Anne Marie en Roel. We had agreed that I would get feedback in a week but didn’t hear anything. Today I got an email back, Roel apologized for ‘putting it on hold’ due to busy work. The Heat/Cold storage needs to be reported through Omgevingsloket. The report is so complicated that I asked for their assistance. The report does not appear to be intended for individuals but much more as a stimulus to hire certified professionals to do this for you.

Section 1. Reporting

There are some complications regarding the reporting of the heat/cold storage. As we can see in the screenshot below:

wko1A certificate number of the designer of the closed ground energy system needs to be submitted. That’s a fairly big problem as I don’t HAVE a certification. Googling for ‘certificering bodemenergie systeem ontwerp’ gives a link to  PDF document (Dutch) of and says the following:

Earth energy is a successful, sustainable technique that’s used more and more often. The expected growth may not lead to proliferation. The government is going to introduce a mandatory certification. BodemenergieNL (previously NVOE) had developed the ‘leergang bodemenergie’ in that context.

Very interesting. But let’s be realistic, I want to put waterlines under my backyard in order to retain some heat energy. Words like ‘proliferation’ make me wonder if this is at all relevant to what I would like to be doing. As owner of a small piece of land I would like to heat up that piece of land during daytime in order to be able to extract some of that heat during nighttime. Doesn’t the sun do that nearly every single day without any certified designer/engineer having any say in it?

Anyway, after that the following quote shows the real purpose in my opinion:

The government will introduce a mandatory certification for earth energy systems. In the context of the SWKO program the govenment has detailed this mandatory certification with the stakeholder. The mandatory certification will apply to consultancy firms, installation companies, drilling firms and maintenane companies.

Who are the stakeholders? That must be those firms doing the work, after all it’s their bread and butter. So in my opinion what we’re seeing here is just another economic stimulus instead of an environment stimulus. While this is fine in some ways, I also sometimes get tired with the hidden motives.

Peculiarly, the PDF of bodemenergieNL says also:

The AmvB earth energie is planned on juli 1st 2013. There will be a transition period of 1 year. After July 2014 only certified companies will be allowed to work on earth energy systems.

So at this date, februari 19th 2014, no certification is required yet. Then why is is mandatory to enter a certification number at the omgevingsloket I wonder.

However, since I’m planning to make this part of my business, it seems like a genuinely good idea to follow some of these trainings and become certified to make a design, install it and maintain it. has a few trainings:

  • Basic Earth Energy (3 days)
  • Specialisation above-ground design and realisation open/closed (3 days)
  • Specialisation underground design and realisation closed systems (2 days)
  • Specialisation underground design and realisation open systems (2 days)
  • Specialisation exploitation open/closed (2 days)

The 4th training won’t be necessary for me, so in total this would mean some 3 + 3 + 2 + 2 = 10 days of training.

Chapter 3. What’s Next?

Well, after building this, I need to get a move on with actually building the greenhouse itself and solar panels for heating.