Hey guys, I'm currently a student and completing my Technical report, the project I've chosen is geothermal Asphalt. I've constructed a prototype and it works but I am struggling on the design part, I have searched a ton and have found nothing on designing the ground loop or sizing the heat pump. I would like to design the ground loop for per km of roadway (1000m) and the road width is 12.95m I have no idea where to look, or if there are any equations available. Any help is greatly appreciated!! Thanks, Jason

So Jason you are using asphalt essentially as a solar thermal btu collector for a water source heat pump?

Sizing a heat pump depends on the load of the area you wish to heat. Capacity of a loop system needs to meet the requirements of the heat pump.

It shouldn't be that hard to develope a formula for BTU's collected by X meters of asphalt on a sunny day.

Next you would need a more conventional collector for nights, cloudy days and snow covered roads. I also would think you would need to research potential negative impact on the road.

jamesATthermalbatterysystemsDOTcom developes hybrid systems with storage tanks to bank btus. Drop him a note.

My goal on the project isn't to use the asphalt as a solar btu collector but instead to use the ground heat, further heated by the heat pump to be then sent through HDPE throughout the asphalt to warm/cool it

I put tubes in my driveway for a similar ideas.... I used concrete and was going cover it with black asphalt researfacing coating. My plans were...heat a pool, warm the ground in preparationfor winter, melt snow in winter, provide hot water for bathing in the summer....I haven't completed the project yet.

So sort of an ice melt thing? Maintaining temperature in an asphalt road is advantageous for......?
Obviously there would be considerable expense in this, just trying to understand cost v benefit.

Anyway to get to the answer of design, you would have to identify the closest major city to your km of road and design parameters (i.e. do you want to maintain 70 year round or keep the surface between 30 and 80 for instance). Are you going to have perimeter insulation?

I suspect you'll be cooling dominated in most areas sout of the artic (or maybe there too) as a good sunny day may easily create twice the btus to reject as a cold cloudy day will require extracted.

I Live in Canada, Ontario and the reason why I would like to use geothermal is to prevent snow from staying on the road. The system wont be on all the time, only when precipitation is detected the system will turn on for the duration of the snow fall and will remain on until the roads are dry.

There is no doubt it will be very expensive, but I hope the long term savings of the system will offset the cost as there will be no need for salt trucks or plows anymore.

During the winter time I would like to maintain a temperature of 3 degrees Celsius (37.4) and during the summer time when the asphalt temperature reaches 50 degrees Celsius the system will turn on, cooling the asphalt preventing damage to the surface

Posted By newbostonconst on 06 Apr 2014 08:38 AM
I put tubes in my driveway for a similar ideas.... I used concrete and was going cover it with black asphalt researfacing coating. My plans were...heat a pool, warm the ground in preparationfor winter, melt snow in winter, provide hot water for bathing in the summer....I haven't completed the project yet.

Whenever you heat something in the summer you will actually be cooling the driveway. How does that "warm the ground in preperation for winter"?

GOY,there appear to be differing opinions on how many btu/sf you can collect from solar. You are going to have to pin down a value before you can answer your other questions.

My goal on the project isn't to use the asphalt as a solar btu collector

GOY, snow melt systems use terrific amounts of energy. Typically, they are employed only in a few places. You first need to calculate the heat loss of your roadway to get an idea of how many geo systems per mile would be required to keep it from freezing.

A black driveway in summer can reach 150° F surface temp in the summer. If my field temp is 50° F and I pump the meth/h2o between the two loops you should move significant amount of heat to the field heating the ground which a portion can be extracted over winter.....

Posted By newbostonconst on 08 Apr 2014 08:31 AM
A black driveway in summer can reach 150° F surface temp in the summer. If my field temp is 50° F and I pump the meth/h2o between the two loops you should move significant amount of heat to the field heating the ground which a portion can be extracted over winter.....

You can't "bank" btu's too long, meaning most of your heat energy will migrate away (the very principle that makes geo work). Do not expect an impact for more than a few days and then only if you jump straight from cooling to heating. Better I think to use that energy for domestic hot water or a pool.

Wouldn't there be a point where having a ground loop large enough to just pump the brine between road surface loop and the ground loop to keep the road above freezing? Not using any heat pump.

Chris

Posted By ChrisJ on 08 Apr 2014 09:28 AM
Wouldn't there be a point where having a ground loop large enough to just pump the brine between road surface loop and the ground loop to keep the road above freezing? Not using any heat pump.

Chris

Ya but the the loop field would have to be huge....would love to have the drilling contract on that

I was hoping the use of a heat pump would make the loop significantly less and once the asphalt is above 3 Celsius the heat pump can basically shut down as long as the temperature does not go below 3 Celsius.

I think anybody would love to have the contract on this Dean haha, for sure it will be crazy expensive.

I haven't thought of the idea of storing energy from the summer, is there any way to bank the BTU's for a long period of time?

"I haven't thought of the idea of storing energy from the summer, is there any way to bank the BTU's for a long period of time?"

You can bank btu's for a short period of time in a variety of ways, but long term storage would likely cost more than the savings you would recognize from it.

I have an old Wirsbo/Uponor snow and ice melting surface condition design manual, just for some reference here are some numbers for you to get you started. My manual is in that silly non base 10 system so sorry for the numbers that you will have to convert. Depending on where specifically you are, I show that you have a 0F to -25F design temperature so lets just assume you are 0F outdoor air temp.
Based on this you then need to figure surface temperature, which you are saying is 3C. i will give you a few different conditions so you can see how many BTU's this would take.

Based on 0F outside temp with 35 degree surface temperature and 0MPH wind you need 83 BTU's per sq foot with 87 degree supply temp for 6" on center and 116 degree supply temp for 12" on center
Based on 0F outside temp with 35 degree surface temperature and 5MPH wind you need 98 BTU's per sq foot with 95 degree supply temp for 6" on center and 129 degree supply temp for 12" on center
Based on 0F outside temp, with 35 degree surface temperature and 10 MPH wind you need 133 BTU's per sq foot with 112 supply temp for 6" on center pipe or 157 degree supply temp for 12" on center which starts to exceed design conditions
Based on 0F outside temp with 40 degree surface temperature and 10 MPH wind you need 152 BTU's per sq foot with 126 supply temp for 6" on center and thats all that design conditions allow
Based on -10F outside temp with 35 degree surface temperature and 10 MPH wind you need 172 BTU's per sq foot with 130 supply temp for 6" on center, no other design condition allows.
Based on -10F outside temp with 40 degree surface temperature and 10 MPH wind you need 191 BTU's per sq foot with 144 degree supply temp for 6" on center

Hope that is enough data points to give you a general idea of what wind and temperaure do to the heating factors/ground loop and heat pump sizing etc.

thanks for the intel

Posted By GodOfYou on 09 Apr 2014 04:39 PM
I was hoping the use of a heat pump would make the loop significantly less and once the asphalt is above 3 Celsius the heat pump can basically shut down as long as the temperature does not go below 3 Celsius.

I think anybody would love to have the contract on this Dean haha, for sure it will be crazy expensive.

I haven't thought of the idea of storing energy from the summer, is there any way to bank the BTU's for a long period of time?

You may be interested in this. http://www.dlsc.ca/how.htm