ᐅ Air-to-air heat pump vs. air-to-water heat pump vs. trench ground collector – Differences
Created on: 12 Dec 2019 10:33
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Neubau2020
Hello,
I am currently trying to decide how the heating energy should be generated.
Here in the forum, I came across the horizontal ground loop collector, which I find very interesting. In conversations with two prefabricated house suppliers, I mentioned that I am considering generating energy with a horizontal ground loop collector. Both times, the response was, "We’ve heard of horizontal ground loop collectors, but never installed one."
One offer included an air-to-water heat pump (Luxhaus KfW55), and the other included an air-to-air heat pump with controlled residential ventilation (Streif Haus KfW40). The house will have two levels, no basement, around 190 m² (2,045 sq ft), on a fairly flat plot with no special features.
I am wondering how the horizontal ground loop collector differs technically and in price from the air-to-water heat pump.
Is the technology inside the house the same, or are there other factors to consider, such as system size and design?
Is the main difference simply that instead of the external unit of the air heat pump, I install the trench and lay the pipes?
What is the price difference?
What about the long-term difference in energy consumption? The air heat pump needs to run continuously on electricity to draw in air—how does it work with geothermal energy from the horizontal ground loop in this regard?
Lastly, a question regarding the air-to-air heat pump:
The sales representative from Streif Haus said that if I wanted to switch from the air-to-air heat pump to an air-to-water heat pump, it would cost about 10,000 euros more. Is that a realistic estimate?
I am currently trying to decide how the heating energy should be generated.
Here in the forum, I came across the horizontal ground loop collector, which I find very interesting. In conversations with two prefabricated house suppliers, I mentioned that I am considering generating energy with a horizontal ground loop collector. Both times, the response was, "We’ve heard of horizontal ground loop collectors, but never installed one."
One offer included an air-to-water heat pump (Luxhaus KfW55), and the other included an air-to-air heat pump with controlled residential ventilation (Streif Haus KfW40). The house will have two levels, no basement, around 190 m² (2,045 sq ft), on a fairly flat plot with no special features.
I am wondering how the horizontal ground loop collector differs technically and in price from the air-to-water heat pump.
Is the technology inside the house the same, or are there other factors to consider, such as system size and design?
Is the main difference simply that instead of the external unit of the air heat pump, I install the trench and lay the pipes?
What is the price difference?
What about the long-term difference in energy consumption? The air heat pump needs to run continuously on electricity to draw in air—how does it work with geothermal energy from the horizontal ground loop in this regard?
Lastly, a question regarding the air-to-air heat pump:
The sales representative from Streif Haus said that if I wanted to switch from the air-to-air heat pump to an air-to-water heat pump, it would cost about 10,000 euros more. Is that a realistic estimate?
S
Strahleman12 Dec 2019 15:36We are currently planning our house with a ground loop collector (DIY) and a ground source heat pump. Fortunately, this is quite straightforward because there is a dedicated forum where many experts discuss ground loop collectors. Special planning software (Trenchplanner) has even been developed specifically for DIY builders. You just need to be willing to study the topic in detail since the number of service providers for installing ground loop collectors is still quite limited in Germany.
As Tego12 already mentioned, there are basically no additional costs. In fact, the opposite is true. If you install the ground loop collector yourself, it is a fairly attractive option thanks to government subsidies (BAFA) compared to an air-to-water heat pump. Currently, there is a 4,000 euro subsidy plus an optional 500 euro load management bonus and an additional 500 euros if you install a solar system larger than 7m² (about 75 ft²). So, up to 5,500 euros total subsidy for new builds. The pipes including accessories can be purchased online for around 1,000 euros, plus rental costs for excavators or fees for the civil engineer. Additionally, the heat pump units usually cost somewhat less than air-to-water heat pumps. So, installation costs are basically around zero. You often still have a good portion of the subsidy left over (depending on pipe length and trench size).
The annual operating costs of a ground source heat pump are about 20% to 40% lower than those of an air-to-water heat pump. Of course, this depends on the actual COP and seasonal performance factors you achieve in reality. However, you definitely won’t pay more than with an air-to-water heat pump. In summer, the ground source heat pump can also provide very inexpensive active cooling, whereas air-to-water heat pumps require a considerable amount of energy for this.
What exactly do you mean by a "large plot"? The definition varies quite a lot depending on the region. If your plot is truly large enough, I would definitely consider the ground loop collector as an alternative. There are basically no disadvantages, and it is a great alternative to the often used air-to-water heat pump.
Air-to-air heat pumps are cheaper because they do not require underfloor heating. In my opinion, however, they are the least efficient type of heat pump.
As Tego12 already mentioned, there are basically no additional costs. In fact, the opposite is true. If you install the ground loop collector yourself, it is a fairly attractive option thanks to government subsidies (BAFA) compared to an air-to-water heat pump. Currently, there is a 4,000 euro subsidy plus an optional 500 euro load management bonus and an additional 500 euros if you install a solar system larger than 7m² (about 75 ft²). So, up to 5,500 euros total subsidy for new builds. The pipes including accessories can be purchased online for around 1,000 euros, plus rental costs for excavators or fees for the civil engineer. Additionally, the heat pump units usually cost somewhat less than air-to-water heat pumps. So, installation costs are basically around zero. You often still have a good portion of the subsidy left over (depending on pipe length and trench size).
The annual operating costs of a ground source heat pump are about 20% to 40% lower than those of an air-to-water heat pump. Of course, this depends on the actual COP and seasonal performance factors you achieve in reality. However, you definitely won’t pay more than with an air-to-water heat pump. In summer, the ground source heat pump can also provide very inexpensive active cooling, whereas air-to-water heat pumps require a considerable amount of energy for this.
What exactly do you mean by a "large plot"? The definition varies quite a lot depending on the region. If your plot is truly large enough, I would definitely consider the ground loop collector as an alternative. There are basically no disadvantages, and it is a great alternative to the often used air-to-water heat pump.
Air-to-air heat pumps are cheaper because they do not require underfloor heating. In my opinion, however, they are the least efficient type of heat pump.
Hi, I initially wanted a trench collector as well, but didn’t want to do it electrically... the heating contractor wanted about 6000 € for it, so in the end I decided to go for drilling instead. It cost a few thousand more, but I didn’t mind.
In the end, I wanted something that works smoothly. The company that was going to do the trench collector hadn’t done it before.
Of course, it’s not cost-effective, but is a new build ever really cost-effective?!
Good luck!
In the end, I wanted something that works smoothly. The company that was going to do the trench collector hadn’t done it before.
Of course, it’s not cost-effective, but is a new build ever really cost-effective?!
Good luck!
mini_g! schrieb:
@Tego12 : Could you share how you approached your horizontal ground collector? Did you select the heat pump yourself? Did you order the collector pipes prefabricated?
Sorry if this has already been discussed here in the forum.
Thanks! miniCertainly, I’ll roughly outline the steps:
1) Research, mainly on the pink forum: about 10 hours (probably could have done it in less, but I really enjoy the topic)
2) Planning with the planning tool on the pink forum and by creating a thread there for discussion, plus coordination with my heating engineer: about 4 hours;
We defined the end of the manifold as the interface. Up to the manifold was my responsibility, from the manifold onward was his. He handled pressure testing and filling, which is no different from a deep geothermal borehole system. I chose the heat pump from his offer. I was very satisfied with the heating engineer and definitely wanted to purchase through him.
3) Ordering materials and planning the process (I ordered through a user on the forum who offered complete packages of two times 300m (984 feet) pipe + manifold + accessories; the manifold was prefabricated, the pipes were just pipes... we had to lay the slinkies ourselves, but that was incredibly easy): about 2 hours
4) Preparation on-site the day before installation: I marked the layout on the ground with spray paint for the excavator operator and brought all materials to the construction site, 2 hours
5) Installation day: excavator + operator + plate compactor (paid), and me + one colleague. The excavator dug according to my plan, my colleague and I laid the pipe. The excavator covered everything up again at the end. The whole thing took 11 hours (but only about 2.5 hours were pipe laying… that went really fast), it was fun and we finished successfully; I also got to practice operating the excavator a bit but handed it back quickly, otherwise it wouldn’t have been finished... ; 11 hours
6) The entry into the house was done by my company using a sewer pipe through the foundation slab; it’s no different from other utility entries, no issues there.
That’s basically it... the commissioning etc. was done with the heating engineer... it’s exactly the same as with a deep borehole system.
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neubau201913 Dec 2019 09:37@Tego12
How much area did you need for your energy pile collector, and what heating load was it designed for?
Is it possible to plant trees and similar vegetation over the slinkies?
How much area did you need for your energy pile collector, and what heating load was it designed for?
Is it possible to plant trees and similar vegetation over the slinkies?
neubau2019 schrieb:
@Tego12
How much area did you need for your horizontal ground heat exchanger, and what was the heating load?
Is it possible to plant trees or similar over the coils? My plot is 500 m² (5400 sq ft), with the garden covering about 300 m² (3200 sq ft). The collector uses the size of the garden (a 1.5 m (5 ft) wide trench running around the edge, with a small loop going into the middle at the end... I laid it straight past the left and right sides of the house). Our soil is somewhere between sandy and loamy. We have an approximately 5 kW heat pump, and the heating load is around 4 kW. According to the tool, our trench would be suitable for up to about 6 kW, so everything is quite relaxed.
You can plant whatever you want above the pipes... they are indestructible (in any case, use the RC "resistance to crack" pipes as recommended in the pink forum).
Basically, nothing can really go wrong unless you damage the pipes. As long as you don’t hit them with an excavator bucket... that’s almost impossible.
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