Ground Source Heating Pipe
- Thread starter philberto
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Doctor Drivel
I recall one in the USA, where they had a large underground water tank and lots of pipe under the ground. The tank can be overground as long as it is insulated. A pump just circulated the water through the loops and back to the tank. This made the water in the tank the same temp as the earth. The heat pump extracted heat from the water (water contains 4 times more heat than earth). The COP was very high.
The COP figures given for heat pumps are the best case example. As soon as the ground temp drops so does the COP.
What is the ballpark for the loops per kW output?
The COP figures given for heat pumps are the best case example. As soon as the ground temp drops so does the COP.
What is the ballpark for the loops per kW output?
Doctor Drivel wrote
The ground area is calculated according to the refrigeration capacity of the heat pump.
Thats the difference between the heating output of the heat pump and its power consumption. Most company's will have performance diagrams for their systems charting the refrigeration capacity or you can calculate either theoretical or actual refrigeration capacity using known data from refrigerant tables relevant to the corresponding refrigerant used.
The extraction rate from the ground varies depending on the type of soil.
A ball park figure of about 20- 25 watts per sq meter can be used.
The smaller the pipe used then the more per sq meter needed. 20mm pipe is laid at 3m per sq meter. 32mm @ 1.5m per sq meter etc.
The ground area is calculated according to the refrigeration capacity of the heat pump.
Thats the difference between the heating output of the heat pump and its power consumption. Most company's will have performance diagrams for their systems charting the refrigeration capacity or you can calculate either theoretical or actual refrigeration capacity using known data from refrigerant tables relevant to the corresponding refrigerant used.
The extraction rate from the ground varies depending on the type of soil.
A ball park figure of about 20- 25 watts per sq meter can be used.
The smaller the pipe used then the more per sq meter needed. 20mm pipe is laid at 3m per sq meter. 32mm @ 1.5m per sq meter etc.
There are many good programs designed to work it all out, juggling ifs and maybe's around in the head is a pointless exercise and practically imposible to get accurate.
Basically you want the collector loops to pick up as much heat as posible, e.g. if the ground temp is 12c then that is what you should be looking to collect. To do that the pump must be sized to suit the size and length of the loops, you need balanced loops to circulate the brine mixure evenly and most importantly to get as much turbulance in the collectors as posible
Got to go to work more later if required.
Basically you want the collector loops to pick up as much heat as posible, e.g. if the ground temp is 12c then that is what you should be looking to collect. To do that the pump must be sized to suit the size and length of the loops, you need balanced loops to circulate the brine mixure evenly and most importantly to get as much turbulance in the collectors as posible
Got to go to work more later if required.
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Doctor Drivel
With boilers you go to SEDBUK and they give the efficiency to an "average" British and climate. OK when coupling a boiler to say a thermal store this pretty meaningless, as peak efficiencies, etc are more important. But at least something is there as a yardstick.
With heat pumps the COP (Co-efficient Of Performance) is peak efficiency only. None condensing boilers can "peak" at 90% plus, yet average is only 79-80% at best - big drop. Once the ground cools around the slinkies the COP falls off quite quickly. This is never mentioned. So, a COP average is needed for say that particular area - ground temps and conditions..
So when the say it has COP 4, 1kW consumed and 4kW output, don't think that will be the case all year around. It will be more like COP 2.
With heat pumps the COP (Co-efficient Of Performance) is peak efficiency only. None condensing boilers can "peak" at 90% plus, yet average is only 79-80% at best - big drop. Once the ground cools around the slinkies the COP falls off quite quickly. This is never mentioned. So, a COP average is needed for say that particular area - ground temps and conditions..
So when the say it has COP 4, 1kW consumed and 4kW output, don't think that will be the case all year around. It will be more like COP 2.
There is no industrial standard as yet so everyone is still learning to an extent.
I agree with the COP being very up in the air so to speak and some installions I've seen would be lucky to break even.
We work on 12c at 1200 mm and can virtually guarantee that or better through the heating season.
If you can centralize the collectors at 600mm, and have all the loops at the same length + or - 10%, preferably with a reverse return on the manifold you should be able to balance the loops and get and even spread across the area.
The pump must be sized to circulate the liquid with turbulance through all the loops, on the other hand too big and it becomes less cost effective, for the same reason smaller 32mm pipes are considerably less cost than bigger sizes, and are also much easier to handle from a labour point of view.
I agree with the COP being very up in the air so to speak and some installions I've seen would be lucky to break even.
We work on 12c at 1200 mm and can virtually guarantee that or better through the heating season.
If you can centralize the collectors at 600mm, and have all the loops at the same length + or - 10%, preferably with a reverse return on the manifold you should be able to balance the loops and get and even spread across the area.
The pump must be sized to circulate the liquid with turbulance through all the loops, on the other hand too big and it becomes less cost effective, for the same reason smaller 32mm pipes are considerably less cost than bigger sizes, and are also much easier to handle from a labour point of view.
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