|
|
|
Equipment / Loop Sizing Software Platforms
Last Post 22 Jun 2016 04:07 PM by docjenser. 17 Replies. |
Sort:
|
|
 Prev Next |
You are not authorized to post a reply. |
|
teshj314
New Member
Posts:39
 |
| 14 Jun 2016 02:49 PM |
|
Have used several equipment/loop sizing software platforms in tenure as a geothermal professional.
Was most fond of Kavanaugh's GCHPcalc, and became familiar with other's as time moved on.
My recent experience with a manufacturer's promoted platform comes with mixed feeling; the software output was explaining how an "undersized" equipment/system was somewhat compatible if not better than an "oversized" system.
Now, by undersizing, I mean to say that as outdoor air temp approached our calculated design day, the undersized unit would simply rely on backup/aux to match the load. Oversizing would mean that the equipment would handle a design day and a little more with all geothermal and no backup/aux.
What I question is how certain the software is at anticipating ground temperature during the approach of heating design days, and the corresponding output of the equipment? I would hope that all bases are covered, but I have not had positive experiences with undersized systems and the initiation of backup to cover the difference.
What do the rest of you all feel. I understand economics, and I appreciate Joe/AMI's input on how to deal with this approach; but it must be said that usually backup/aux comes in the form of expensive electric resistance elements, and not a powerful/robust fossil fueled device.
I keep going back to my in-the-field experience of seeing ground/loop temperatures in the 30's, with plenty of winter left to experience.
I'm a firm believer in a coupled global/terminal control system for initiating backup/aux; one where we have an OAT, an equipment temp sensor, and a distribution temp sensor. Upon drop or rise in temperatures, we initiate second stage or backup/aux.
Interested in hearing some of your thoughts.
I'm in Climate Zone 5, btw.
Thanks. |
|
|
|
|
|
|
docjenser
Veteran Member
Posts:1400
|
| 16 Jun 2016 01:07 AM |
|
I continue to see significant deficiencies in the design software, but they get people in the ball park with an acceptable safety margin.
I am in climate zone 5/6, Buffalo NY, and have significant difference in OAT (30F in locations less than an hour apart), but the software only has Buffalo Airport in its database. Unfortunately, none of customers live at the airport.
I started to monitor all my sites, so I have feedback between design parameter and real world how they actually perform, and learned what factors actually influence performance and which don't.
I learned to make equipment larger, and push loop field to the edge with minimal performance penalties but at much lower installation costs.
I also find that variable speed equipment changes everything, from the absence of loop pulsing to the fact that the penalty is minimal or actually it is beneficial if it is "too large".
There is so much guesswork in the load calculations, which influences actual performance much more than more other design parameters.
We are guessing wall insulations in retrofits, and ground conductivities and annual performance most of the time.
Loops are very forgiving, who says that 28F minimum entering water temp is bad?
Looking at the big picture, we will have to design for 110% of the load, since it is not thesible to create a winter peak for the grid which is larger than the current summer peak in heat dominated climate. For the same reason air source heat pumps are not thesible in heat dominated climate. We simple have not enough grid and power capacity to to have all the geo systems go into aux heat at the same time, or have air source HPs run at a COP of 1.0
So I have changed with that understanding that electrically driven geo heat pumps are the only current solution to get away from fossil fuels for space conditioning, since electricity is the only thing we can make renewable, and the winter peaks created by aux resistance heat are not sustainable. And also not necessary with variable speed technology.
In terms of software, I like LoopLink for larger residential and commercial jobs, and I use it as in insanity check. |
|
| www.buffalogeothermalheating.com |
|
|
teshj314
New Member
Posts:39
|
| 16 Jun 2016 01:15 PM |
|
docjenser, thank you for your well defined response.
Knowing your AO, I agree that there are prevalent temperature swings in a 60 mile radius.
I too have found myself relying on the several platforms to calm my nerves prior to final submission of design.
It is in fact an insanity check.
I have no issues with EWT of 28F, I have issues with this temperature when it is only late January/early February; modeling and performance testing of the building was done prior and after the installation. What was not performed was a ground thermal conductivity test.
Has anyone ever performed one of these conductivity tests?
|
|
|
|
|
docjenser
Veteran Member
Posts:1400
|
| 16 Jun 2016 01:48 PM |
|
http://welserver.com/WEL0477/
http://welserver.com/WEL0447/
Why would you be concerned about an EWT at 28F at the end of Jan?
The ground would stabilized since it would transport as much heat to the borehole as the system extracts, plus it would go through a phase change, releasing a large amount of heat if it drops below freezing.
Above are 2 links where you can see how the loops stabilize in the middle of the winter at the beginning of FEB.
None of the design programs account for phase change or replenishing of heat through the ground. They are all based on line heat transfer equations. Once you monitor enough systems and understand how this all works, pretty much every design program flies out of the window.
But they keep you legally safe.
In view of that a one or 2 day ground conductivity test is kind of questionable for me too. I personally spend the money on higher conductive grout, or put an extra borehole in there to begin with.
I like to have an indicator on how the drilling condition are, although even that is none predictable too.
|
|
| www.buffalogeothermalheating.com |
|
|
docjenser
Veteran Member
Posts:1400
|
| 16 Jun 2016 02:04 PM |
|
Just to add since you seem more in the professional/commercial world, I have attached a system for a 24 apartment with 5 restaurants/bistros.
Monitoring is for 2015.
You can see 2 graphs for the temps for 2015, one going back 12 months, the other going back 1 months with higher resolution.
11.5 months ago the loop dipped down to 29 F around Jan 10th (polar vortex), then actually got warmer again until end of Feb (second polar vortex) when it went down to about 28F, and stabilized for another couple month after that. So it did not continue to drop but actually gained temperature under lesser load, only to peak down again under extreme conditions.
PS could not attach file due to size limits here.
You might want to move the discussion to the geo-exchange forum which does not have the file size limitations
https://www.geoexchange.org/forum/#geothermal-heat-pump-info.290
Here is this year's link:
http://welserver.com/WEL0714/ |
|
| www.buffalogeothermalheating.com |
|
|
teshj314
New Member
Posts:39
|
| 16 Jun 2016 02:42 PM |
|
Doc,
Thank you.
I should have clarified more so that it is not my fear of a cold (EWT=28F) fluid temperature, but a cold ground temperature.
I often profess the need to understand the benefits of latent energy released during phase change, but I can't ignore the phenomenon of what happens after the ground temp, not fluid temp, dipping below freezing.
It is as this point, from my experience and understanding, that our systems will struggle to continue to extrapolate the heat energy from the ground, as a frozen ground is a well insulated source; so energy needed for recharging the source is impeded by the insulating characteristics of a frozen layer.
Which is why I posed the question about coupling our system designs/software outputs with final installed designs. I am having a hard time understanding how a software platform can churn out all these different models (mind you we have selected climate zones, ASHRAE locations, inputted a ground type, and inputted our block loads) and yet they "recommend," through economic anaylsis, that it is safe to under size a unit and rely on aux heat.
My experience is that an improperly controlled, undersized uni,t is going to draw the ground to undesirable temperatures, where equipment performance is inefficient and struggling at best.
Maybe what I am wishing for is a "control" section of the modelling software?
Doc, thank you for the links. I will take some time to peruse what you have linked for me. I am very curious to see what these systems have provided considering the winter of 2014/2015.
Thank you again. |
|
|
|
|
docjenser
Veteran Member
Posts:1400
|
| 16 Jun 2016 05:13 PM |
|
Posted By teshj314 on 16 Jun 2016 02:42 PM
It is as this point, from my experience and understanding, that our systems will struggle to continue to extrapolate the heat energy from the ground, as a frozen ground is a well insulated source; so energy needed for recharging the source is impeded by the insulating characteristics of a frozen layer.
I understood you meant ground temp, however, we are limited to measure the EWT and LWT as a matrix.
The monitoring indicates the opposite, namely that the loop stabilizes when the EWT drops around the 30F mark.
Heat continues to be transported toward the borehole, and phase change seems to have a huge amount of residual capacity to supply. |
|
| www.buffalogeothermalheating.com |
|
|
jonr
Senior Member
Posts:5341
|
| 16 Jun 2016 10:07 PM |
|
as a frozen ground is a well insulated source Frozen ground typically has somewhat higher thermal conductivity than non-frozen. At ~33F EWT in April, one would get better efficiency (BTU per KWh) from an air source heat pump. But most efficient often isn't most cost effective (there are even times when resistance heat does well for this). If anyone is very concerned about peak grid load - use thermal storage (unlike the ground, it requires little or no energy to extract at time of use). |
|
|
|
|
docjenser
Veteran Member
Posts:1400
|
| 17 Jun 2016 12:37 AM |
|
Posted By jonr on 16 Jun 2016 10:07 PM
At ~33F EWT in April, one would get better efficiency (BTU per KWh) from an air source heat pump. But most efficient often isn't most cost effective (there are even times when resistance heat does well for this).
If anyone is very concerned about peak grid load - use thermal storage (unlike the ground, it requires little or no energy to extract at time of use).
Silly comment.
Shall we install an air source heat pump for the month of april only, since I can find a few days with outside temperatures which might run more efficient.
2nd silly comment about peak grid load. We have thermal storage, it is called the ground.
States are moving towards reducing or eliminating CO2 from space conditioning. Only electrically driven heat pumps can do this, and only geothermal heat pumps in cold climate.
Do the math and tell me how this should work with another thermal storage solution, both without creating a significant winter peak or killing the overall efficiency. |
|
| www.buffalogeothermalheating.com |
|
|
teshj314
New Member
Posts:39
|
| 17 Jun 2016 09:07 AM |
|
In regards to additional equipment specification for Aux/Backup; only the commercial code states that the designer/installer must provide a "backup" source for heating in a heat pump application/installation.
Well versed geo installers know that you always provide some form of backup/aux.
Now, do I want to specify a low inertia source for backup/Aux, or a high inertia source? Personal preference states I would prefer the high inertia source, but economics and system conditions have to be considered when making this choice.
I have to agree and state that my opinion would never be to specify an air source heat pump as my choice for backup/aux; especially when knowing a building always requires a source of potable hot water.
My fear of a frozen HX source stems from a project I designed and oversaw in upstate NY, Columbia County. A bank of 5 W2W units were coupled with a pond/lake heat exchanger. This equipment plant was used solely during construction period conditioning. One day, before winter was over and spring had sprung, the contractors arrived to the job site to find the building without heat, and a bulge cresting in the pond/lake.
Turns out that the plant had run for so long, and without rest, that the surface water HX had frozen, broken its restraints, and floated to the surface and cracking the ice of the surface water body.
That instance is why I question ground source HX temperature, not the EWT. I know that I can continue to get heat from EWT 32 or less, and that I am complacent with. But what about my ground temperature when its starts to get that cold? Upon phase change and latent heat release, I need to understand the swing time required to recharge the ground and my subsequent equipment's performance of continuing to match the loads.
Regards. |
|
|
|
|
jonr
Senior Member
Posts:5341
|
| 17 Jun 2016 10:03 AM |
|
Silly comment. Shall we install an air source heat pump for the month of april only, since I can find a few days with outside temperatures which might run more efficient.
www.buffalogeothermalheating.com
Wow, point out that something isn't cost effective and all some people can come up with is that it isn't cost effective. And some name calling. |
|
|
|
|
teshj314
New Member
Posts:39
|
| 17 Jun 2016 02:07 PM |
|
jonr,
I am a fan of anything that is not site specific fossil fuel driven. Having said that, an ideal setup would always be to utilize a vapor compression cycle to create heat; whether my source is the air/ground/waste heat stream.
That is why I am so thrilled with heat pump equipment; identify a source, tap into it, and use it.
My only reservation is this choice of redundancy of heat pump compressors for Aux/backup; how would you propose to intertwine the two?
Having a separate heat pump aux system would certainly require an additional DX coil (HX) if being applied to an air system.
Two DX coils in series would affect fan performance and increase the static pressure of the system, so are we looking at a dual circuit DX coil?
Need more insight from you as to how you would propose this setup, if in fact you are proposing it at all.
I tend to design with the intent of 100% geothermal, with aux/backup also being @ 100%.
This stems from my regions experience with air source heat pumps that were installed in the 1980's, and failed to deliver.
Knowing that we need a high temp system to deliver potable hot water to the building, I look to that infrastructure for way to act as my aux/backup source.
I am curious to see what you might be saying or thinking.
Regards.
|
|
|
|
|
docjenser
Veteran Member
Posts:1400
|
| 17 Jun 2016 04:52 PM |
|
Posted By teshj314 on 17 Jun 2016 09:07 AM
In regards to additional equipment specification for Aux/Backup; only the commercial code states that the designer/installer must provide a "backup" source for heating in a heat pump application/installation.
Well versed geo installers know that you always provide some form of backup/aux.
Now, do I want to specify a low inertia source for backup/Aux, or a high inertia source? Personal preference states I would prefer the high inertia source, but economics and system conditions have to be considered when making this choice.
I have to agree and state that my opinion would never be to specify an air source heat pump as my choice for backup/aux; especially when knowing a building always requires a source of potable hot water.
My fear of a frozen HX source stems from a project I designed and oversaw in upstate NY, Columbia County. A bank of 5 W2W units were coupled with a pond/lake heat exchanger. This equipment plant was used solely during construction period conditioning. One day, before winter was over and spring had sprung, the contractors arrived to the job site to find the building without heat, and a bulge cresting in the pond/lake.
Turns out that the plant had run for so long, and without rest, that the surface water HX had frozen, broken its restraints, and floated to the surface and cracking the ice of the surface water body.
That instance is why I question ground source HX temperature, not the EWT. I know that I can continue to get heat from EWT 32 or less, and that I am complacent with. But what about my ground temperature when its starts to get that cold? Upon phase change and latent heat release, I need to understand the swing time required to recharge the ground and my subsequent equipment's performance of continuing to match the loads.
Regards.
I don't see a problem to design with a 100% backup in the future, if the heat pump fails let one cheap (upfront) electric heat element come on and provide emergency backup. What we cannot afford is to switch over to electrically driven (geo) heat pumps and have them all go into supplement heat mode on the coldest day of the year. That would collapse the grid, and the geo industry would have created a nightmare. So I am speaking of emergency heat, not supplement heat.
In your example the ice formation on the pipes made the HX buoyant,
I have seen that too on some 3rd party installed systems when the pond loops were to close together so ice was forming on the outside of the pipes, floated the loop to the surface, were now exposed to 32F water or colder surface temps, and not 39F water, and caused the EWT to drop below 20F and locked out the HPs.
But I would argue that it was a poorly designed pond loop which caused this, where the pipe density was too high so stratification did not work. Once you loose the warmer water floating by your loops the EWT will drop extremely quickly. So ice formation is your enemy in pond loops, but your friend in ground loops.
Ground behaves very different in that heat is constantly moved towards the boreholes or horizontal pipes. It needs to be connected to more volume and does not depend on stratification.
I was worried would would happen after the phase change, but in reality ground further away from the borehole would undergo phase change, and now the ice cylinder has a larger diameter, meaning mass.
We did a project where we did put in some temp sensors 1 ft and 3 ft away from the borehole at 8 ft depth, and run the loop down to 22F EWT by shutting down other circuits/boreholes.
It stabilized at 22F, we could not run it down further, even with 6 ton equipment on a 2 ton loop. We got the 1ft sensor to drop to 29.3F, and the 3 ft sensor always stayed at least 3.5F warmer, but we could not get it below freezing. I am getting much more gutsy with driving the temps down further after having the monitoring done for some years.
I learned that the loop can take a lot of abuse, as long as flow, antifreeze etc is OK. Again, loop performance is not about line heat transfer only, and not accounted for in the software design. |
|
| www.buffalogeothermalheating.com |
|
|
jonr
Senior Member
Posts:5341
|
| 18 Jun 2016 11:22 AM |
|
teshj314: Sounds like your design goals are a) to not burn any fossil fuel on-site and b) to have a 100% backup that would cover something like compressor failure (but not an electrical outage). Not clear what your goals are in terms of efficiency vs cost (balancing initial cost with operational cost). Most people want some mix of the latter, which is where using a little bit of resistance heat usually does well. ASHP was mentioned just to make the point about efficiency vs cost effectiveness (ie, it's unlikely that someone wants to optimize exclusively for the former - that will be very non cost effective). That being said, an ASHP may be a practical backup for geothermal AC. And if you have it in place for AC backup, it's probably cost effective and efficient to run it under some temperature conditions (cold and hot). |
|
|
|
|
docjenser
Veteran Member
Posts:1400
|
| 18 Jun 2016 02:55 PM |
|
Posted By teshj314 on 17 Jun 2016 02:07 PM
Knowing that we need a high temp system to deliver potable hot water to the building, I look to that infrastructure for way to act as my aux/backup source.
I am curious to see what you might be saying or thinking.
Regards.
I am trying to follow you here. Why would you need a backup for the source? Unless you have concerns that your source cannot carry the load. Then you make it bigger, increase the conductivity, or put the bores further apart, or some other design tricks.
If you use heat pumps also to make your potable hot water, again, not sure why the need for backup.
Maybe you could elaborate further..... |
|
| www.buffalogeothermalheating.com |
|
|
docjenser
Veteran Member
Posts:1400
|
| 18 Jun 2016 02:59 PM |
|
Posted By jonr on 17 Jun 2016 10:03 AM
Silly comment. Shall we install an air source heat pump for the month of april only, since I can find a few days with outside temperatures which might run more efficient.
www.buffalogeothermalheating.com
Wow, point out that something isn't cost effective and all some people can come up with is that it isn't cost effective. And some name calling.
No intended name calling. Just pointed out how useless your comment was. What is the point that you might find some days in April with warmer weather when an air source heat pump might run more efficient that a ground source heat pump? |
|
| www.buffalogeothermalheating.com |
|
|
teshj314
New Member
Posts:39
|
| 22 Jun 2016 11:22 AM |
|
Doc,
Yeah, I know what I wrote is confusing regarding backup sources.
The commercial code states that a backup source must be provided for heat pump designs; residential project don't call for it but reviewing building departments ask about it.
Typically, my residential clients are lead to believe that all-electric is the way to go; therefore fossil-fueled sources are usually not considered for design or installation.
Since I am looking for a high-inertia backup source, I prefer to utilize a fossil fueled source for this component; there are just too many benefits to having this feature to not consider. This is especially true when dealing with a renovation/retrofit.
The thought occurred to me recently a strategy I used, implemented, and defended, where I added an extra W2W module to a bank. My argument was that the extra compressor in the bank would suffice as backup should I lose a compressor. For that instance, the design was approved.
Your point of using electrical backup can create a grid problem is duly noted. Having never considering this, I'm glad that you have brought that to my attention.
I should also point out that using electrical backup in an auxiliary approach, when exceeded design heating days are being experienced, comes at the expense of connected amperage capacity of the building. A 20 kW aux heater requires 2x 60 amp circuits, so it gets expensive. I've done the math to show the cost benefits of sticking with a fossil fuel source and it's pretty much a wash.
As you very well know, the art of designing an efficient geo system is directly correlated to costs, which makes the exercise all the more enjoyable.
Thank you for all of your intelligent input.
I would like to point out that the frozen pond loop case was a Slim Jim Geo Lake Plate application.
It makes sense that excessive run times and continuous load would result in a frozen heat exchanger considering the remarkable heat transfer properties of the plate material. From my following research, the Slim Jim product application is kind of frowned upon in the industry, as it connectivity to the system creates an imbalance to the flow of energy throughout the system.
Thanks again.
|
|
|
|
|
docjenser
Veteran Member
Posts:1400
|
| 22 Jun 2016 04:07 PM |
|
May be you could send me a link to the commercial code requiring backup. They usually refer to air sourced heat pumps, since ground source heat pumps would technically not need back up if design is for 100% load.
So there is difference between backup (in case of emergency or failure of the equipment) or supplement heat (making the equipment smaller for cost reasons) and supplement a small percentage of the load with another heat source.
Emergency heat I see simply being covered by electric strip heat. Cheap to install, maintenance free, the only thing is the generator requirements in case of a power failure.
Supplemental heat is different animal. where I have evolved over the years. It is not desirable from a 10,000 ft view to have all the heat pumps using partial electric resistance heat at the same time. It will collapse the grid if we are changing over to the electrification of the heating sector, which we will do soon or later.
We do standard backup for single heat pump installation, only in multifamily buildings or certain commercial spaces I do design without backup for the individual units. But I design with redundancy for the central pumping. Not a big deal if 1 out of 30 heat pump fails, but if a central pump fails, all 30 heat pumps are off.
Electric has a low inertia what you want for backup. You want it to be on quickly in case you need it.
Not sure if back up needs 100% since even on a design day it should be OK to heat the space to 60-65 F until the technician arrives. Furnaces don't have 100% backup either, most have none.
Indeed the Slim Jim is prone to freezing since their capacity specs are not keeping up to the promise (in my humble opinion). That is why we put exclusively slinkies into pond loops. The issue is that you are trying to exchange too much heat on a small surface, and the stratification has trouble keeping up and flowing enough warmer water to the very cold plates. Put a pump in front of the plates and it actually works pretty well. I compare it to an air coil without fins. Small heat exchange area, very conductive, but how is the overall performance without airflow over the coil? |
|
| www.buffalogeothermalheating.com |
|
|
| You are not authorized to post a reply. |
|
Active Forums 4.1
 |
Membership: |
 |
Latest:
croccohvacusa |
 |
New Today:
0 |
 |
New Yesterday:
1 |
 |
Overall:
35027 |
 |
People Online: |
 |
Visitors:
219 |
 |
Members:
0 |
 |
Total:
219 |
|
|
|