Loop for office building (25 total tons)

GRTI Contact?

Hi Eric-
I am interested in using GRTI for a conductivity test. Do you have contact information you can share? Thanks
Matt

 

Nick Harrington
Technical Support Engineer
Geothermal Resource Technologies, Inc.
(605) 542-3636 ext. 110

 

Thank you sir.

 

No problem.
Enjoy!

 

Among my "thoughts" were to apologize for not commenting on this sooner.
Because vertical loops "perform better", we make them shorter. This has negligible impact on the performance of your heat pumps.
Horizontals are designed for the same temp parameters as verts (generally 30-90F) loop length varies, but not EWT.

Longshore, If your system is already in place, what is the purpose of conductivity testing?

 

Conductivity Testing

Hi Joe-
I am looking at a new project with possibility for multiple systems in same geologic setting. I am planning to install one test loop and perform conductivity to make sure I properly size ground loops. I am expecting ideal ground conditions (wet sand) similar to system at my residence with conductivity about 1.4. I will let you know what we find out.
Matt

 

Time to update you all on what happened. We built a building with 41 tons of GHP serviced by 32 wells using WF series 5 units.

The building concept changed from a 28,000 SF two story structure to a 35,000 SF single story. Lots of reasons for this, eliminated two sets of bathrooms, two break rooms, an elevator, two sets of stairs, and it was socially more suited to the business (no status associated with being up or down). Being single story meant we had far more exposed surface area, mostly roof, so that would hurt HVAC performance. However, I calculated that the penalty would be about $1500/year, and the maintenance and inspection of the elevator was going to cost about that much, so no net real cost in the end. And as you will see later , it wasn't that much penalty.

The footprint of the building ended up 160 x 216 ft. You can access the plans and other documents for the building here:

tinyurl.com/ciholas1

In particular, file geo-wells-5.pdf shows the layout of the 32 wells we drilled UNDER the building. There are 8 groups of 4 wells each, radiating out from a header box. All the wells and headers were built before we did anything else, all the rest of the site work happened after the header box was up, so I had to locate the wells and header box carefully since that located the entire building. Here is a photo of the completed header box in the open field.



Each well is 300 ft deep and uses PE4710 SDR 11 HDPE pipe, 3/4" diameter. Well set headers are PE4710 SDR 11 1.5". The drawing calls for both an east and a west spare header of 3" diameter, but that proved to be impractical, so we did 2 sets of 2" to the east and nothing to the west. Early indications are that I won't need this, but it was in case of some major well system disaster or needing more capacity.

All total, there is about 4 miles of HDPE pipe in the ground under the building. Each well was leaked checked individually, and then well sets leaked checked after headering. I kept pressure on the wells during the construction process with gauges to detect any problem. We never had any, and so far, the entire well system doesn't appear to leak at all now 9 months after filling and flushing. We did discover ONE loop pipe set with a shipping defect that caused it to have a hole, but fortunately we found this prior to installation and got it replaced.

Here is the header box prior to drywall after the building pad, floor, structure and studs are up, nearly a year later:



We settled on using 9 zones with a mix of 4 and 5 ton WaterFurnace Series 5 units. All units came equipped with variable flow centers as I decided on individual pumps rather than one large main pump for redundancy reasons. Also, the variable flow pumps were much more efficient than the standard flow centers, so lost power was not as much of an issue. The total tonnage came to 41 tons (five 5 tons units, four 4 ton units). We got an upgraded sensor package on the WF units so we can monitor various operating parameters.

Two of the units (most interior zones) were equipped with desuperheaters for DHW. They serve a 50 gallon highly insulated water heater with electric backup. The building has no showers, so hot water is only for kitchen and bathroom had washing.

A key feature of the building is that it has metal insulated panels, 4 inch thick for the roof, 3 inch thick for the walls. We also did careful foundation insulation so we have what is known as "continuous insulation". We were very careful about thermal breaks and we have vestibules at every door (including the overhead freight door, which is also insulated metal panels). Our balance point for the building is very low, mid 30s to low 40s depending on who is in the building. Thus our dominate use is cooling. That is one reason I made the well system so big and so spread out, I wanted to avoid year over year thermal saturation of the well field.

Now the perceptive among you will realize that we had 8 well sets and 9 units. To deal with that, we built a header system that combines all the wells into one system, everything shares the same fluid. Here it is:



The wells come up in a chase and convert to PVC SCH 40. You can see them in the background of the photo which was taken on the mechanical mezzanine of the building. The wells are then headered together in one large supply and return header, slanted so that sediment falls to the right and air goes to the left. The system has PVC ball valves that can isolate any well set or any GHP unit. A set of check valves (clear, you can see who is running) prevent reverse pumping through inactive units.

If you look at the building plans (available at the web link above), you can see we centralized all the GHP units into one mechanical room. This meant long ducts, but short everything else (loop, water, drains, power, control, etc). The mechanical room is built over our break room and bathrooms, and I put a corrugated steel floor slanted to drain to a central gutter. The entire room thus drains without causing problems below. You can see the central gutter opening in the floor in the picture. The room is 28 x 66 ft, so quite sizable and VERY easy to work on the units. No service man has to open up suspended ceilings and rain dust down on the office workers. The units are VERY quiet naturally, but now that they are far away from the serviced rooms, nobody knows when the units are on or off, totally silent. Noisy HVAC at our previous building was a common complaint.

You may notice that the pipes are not insulated. First, that would be a lot of work and expense. Second, in the general case, the building is cooling, so the water is getting hotter rather than cooler. As long as the dew point of the air in the attic is below the water coming out of the ground, I won't get condensation. If we do occasionally get condensation, then it drains on the mezzanine deck harmlessly. In practice, operating now for about 8 months, we've not had any condensation, and it was VERY humid in the building early on. Since our dominate mode is cooling, any heat transfer to the well water is good, so there's no particular reason to carefully insulate the pipes functionally.

We also elected to run pure water as the fluid, no anti freeze. Again, the predominate mode is cooling, so we are going to heat up our well system rather than chill it. The units are all set for open loop freeze protection, so they will fault out if we ever get low loop temperatures. So far, in the coldest of days (0 F recently), no loop EXIT temperature has gone below 50 F. The use of pure water made flushing simple (just use municipal water, header system valved to make that easy, so no flush cart involved).

If we ever find that we need anti freeze, I can add that. I would use methanol. Right now, pure water is the most effective, most heat transfer and least pumping friction.

As part of the electrical design, all the HVAC units, the ventilation, and the hot water are run off one subpanel. I have a separate private power meter that monitors the energy use of just that panel. Over an 8 month span, I calculate that I have used about $200/month to heat and cool the entire 35,000 SF building. This must be one of the most energy efficient buildings around.

My initial calculation was the single story concept would cost $1500 a year extra to heat and cool. Now it seems like that was considerably overestimated, probably only about $700.

As to capacity, no unit has ever gone to second stage even on the hottest day or the coldest night. It seems the 41 tons is about 30-40% higher than I truly needed. But we have not yet filled the building to capacity, so some reserve is good. My architect tells me that a commercial building is typically sized at 400 SF per ton. We are about 860 SF per ton and he was a bit unsure we should go that far. Now it seems I could have gone to 1000 or 1100 SF per ton.

Other aspects of the building contribute to the low energy use. The lighting is all high efficiency T8 fluorescent or LED and we lit the building to half the typical office building standard (and no one really notices that or complains).

Presently, one unit is in lockout, our first fault. The FP2 sensor went out on it and the unit locked out. We only discovered this a few days ago when we noticed the rear rooms were about 3 degrees colder than normal. The unit had been in lockout for a few days and no one noticed! We still don't have it repaired (HVAC guys very busy with recent cold snap here in the Midwest) but we aren't in bad need of it. I suspected the loss of any one unit would not be a big deal and so far, this has proven to be true. This is good news!

We are presently working on a monitoring system that takes all 9 GHP units and logs parameters 24/7 from the AID port. We already have the units on the network (we bought cheap RS485 to Ethernet adapters). We are also going to put the power meter on the net and log it all together.

I welcome questions and comments about the system. You are also welcome to come visit it if you like and I will show you want we got. www.ciholas.com.

Mike C.

 

Very nice!!! Thanks for the update