Mechanical Review of the Geothermal System (GeoExchange System Fault)

Written Review of the Air-Ease Geothermal System by Project Engineers

Mechanical – Electrical – Plumbing – Fire Protection

Re: Review of the mechanical systems at the Residence

At your request I visited the site listed above and reviewed the mechanical systems and went over your concenrs regarding sub-contractors' responsibilities. My findings at the site and comments on industry standarts are as follows:

1. This was a design-build mechanical contract. Therefore the mechanica suscontractor has the responsibility to provide you and the homeowner with the following documentation,

a. All system sizing calculations including, but not linited to, all manual-J or other load calculations performed, R-values assumed, infiltration and ventilation rate assumptions, allowances taken, etc.

b. All cut sheets, installation manuals, operation manuals, user manuals, and maintenance manuals for each type and model of equipment provided and/or installed, including all heat pumps, fans, coils, condensers, heaters, boilers, pumps, circulators, and valves, thermostats, etc.

c. A listing of the utility requirements of each piece of equipment in the M.C. Scope of work. (This should have been provided prior to the start of any MEP construction.)

d. A site showing the geoexchange system layout with all depths (invert elevations), dimensions and reference locations clearly indicated.

e. A schematic system diagram showing all equipment, piping, manifolds, valves, and sizes and design flow rates indicated.

f. A ductwork plan showing all supply and return ductwork from fan unit to terminals with duct sizes, damper locations and design CFMs clearly indicated.

g. A plan of all radiant hydronic zones with manifold and thermostat locations clearly shown and loop designations corresponding to manifold valve labeling clearly indicated.

h. Documentaton attesting to the chemical composition of the antifreeze solution, how it was mixed, and wheater it was tested.

i. Driller's logs for each geoexchange well as grouting materials and methods.

2. Unless specified otherwise in the contract documents, it is the standard in the industry for the general contractor to provide power and plumbing services to within 4'-0” of the mechanical subcontractor's equipment with the mechanical contractor responsible for final electrical and plumbing connections. These may be performed by the mechanical contractor himself or his designated subcontractors, but often the M.C. will contract with the plumbing and electrical subcontractors on the job. In any event, the M.C. Is expected to supervise the work and be responsible for these connections. The reason for this is to avoid conflicts between trades in the event that there is an equipment failure or warranty issue with regard to any mechanical equippment.

3. It is the design-build mechanical subcontractor's responsibility to coordinate manifold locations, sizes and openings with the framing and drywall contractors prior to the start of their work. While I am not aware of any industry standard, on my own projects I always specify that the M.C. Shall furnish all access panels in non-fire-rated assemblies (to be installed by the drywall contractor) and shall coordinate access panel sizes and locations with the general contractors in all fire-rated assemblies.

4. It is my understating that the mechanical subcontractor's load calculation gave a heating load of approx. 64 kBTUH. It is also my understanding that the M.C. Choose to install a system sized at approximately 80 kBTUH. Without having the M.C.'s load calculations, cut sheets, and the architectural plans I cannot comment on the accuracy of the 64 kBTUH load.

5. I do find however that it is unusual and questionable for the mechanical contractor to size the geoexchange system at 125% of the calculated heating load. Geoexchange is one of the most efficient and reliable forms of heating, but it is also, by far, among the mostcostly per BTUH to install. For this reason geoexchange systems and heat pumps should be designed to provide not less than 70% and not more than 105% of the calculated heating loads. (See Canadian Standards Association CSA-C448 Standard.) Good geoexchange designers typically err on the low side of this range. The reason for this is this is that 70% of the peak heating load will satisfy the heating need of the home about 95% of the time. Thus the great efficiency of the geoexchange system will provide the necessary heat for 95% of the heating hours. During the remaining 5% of those hours the geoexchange heat pump is usually supplemented by an inexpensive boiler or water heater which, while it has lower efficiency, is only needed a small (~5%) percentage of the time. This kind of design also has the advantage of providing a secondary heat source in the event of a failure of the geoexchange heat pump or (as can happen toward the end of the heating season) when the ground source heat reservoir becomes exhausted.

The home has no supplemental heat source and (based on the information that you provided) it appears to me that the cost of the geoexchange system was inflated by significant over sizing. (Please note that if it was the intention of the homeowner to heat the home exclusively by geoexchange and the mechanical subcontractor was so instructed then my comments regarding system over sizing are moot.)

6. It is the mechanical contractor's responsibility to furnish and install all outside air intakes and exhaust complete with rain caps and bird screens.

7. Per the IECC, all ducts (other than supply ducts in attioc spaces) shall be insulated with a minimum R-6 insulation. Furthermore, outside air duct insulation should be wrappedwith a moisture barrier to prevent condensation.

Otherwise I found that the work at the residence to be executed in a professional and workman-like manner. If you would like my assistance in revieweing the as-build documentary materials to be provided by the mechanical subcontractor I would be happy to do so.

Christopher J. Wieczorek, P.E.

Original Document

Geoexchange system review
A written mechanical review of the Geothermal System designed by Air-Ease

Air-Ease Geothermal system review
125% versus 70% heating load