This credit is broken down into three parts: the prerequisite for HVAC Design & Installation (EA 6.1), High-Efficiency HVAC (EA 6.2), and Very High-Efficiency (EA 6.3).   Energy savings can be achieved by sizing the equipment appropriately and selecting very efficient, ENERGY STAR rated equipment.  The prerequisite is as follows:

a. Design and size HVAC equipment properly using ACCA Manual J, the ASHRAE 2001 Handbook of Fundamental, or an equivalent computation procedure.

b. Install HVAC equipment that meets the requirements of the ENERGY STAR for Homes national Builder Option Package.

c. Install ENERGY STAR labeled programmable thermostat (except heat pumps and hydronic systems).

For (a), our subcontractors did use Manual J to size our system.  (The term “properly” is open to debate, though.)  We also have ENERGY STAR programmable thermostats, meeting (c).  Then, for efficiency levels, there is a table of incomprehensible numbers that we need to exceed to meet the prerequisite or to garner any points.  There are minimums for: central air conditioners and air source heat pumps; gas, oil, or propane furnaces; gas, oil, or propane boilers; and ground source heat pumps (divided into open loop, closed loop, and direct expansion).

Let’s tackle this one at a time, for our climate zone and our system (which is comprised of a closed loop ground source heat pump with a back up boiler powered by natural gas, a side-arm tank that preheats our hot water whenever the pump is running, a heat recovery ventilator, and air source heat pump for air conditioning).

For cooling systems, Central AC and air source heat pumps must be ≥ 13 SEER for the prerequisite, ≥ 14 for 2 points, and ≥ 15 for 3 points.  SEER, I learn, is the Seasonal Energy Efficiency Ratio.  It is the cooling output (in BTUs) divided by the total electric energy input (in watt-hours); the higher the rating, the more efficient the system.  Since 2006, the U.S. has required that all new air conditioners have a minimum SEER rating of 13 — so we know we at least meet the prerequisite.   Our Green Rater, Jimmie Sparks, has told us that our cooling rating is 17. 5 EER.  The EER is the same thing as the SEER, except that the SEER evaluates the equipment over a given time period in typical weather.  According to Wikipedia, typical EER for residential central cooling units = 0.875 × SEER.  So, our SEER would be 20 — greatly exceeding the 3 point threshold.  But we can’t get all the points just for cooling…only half.

Moving on to our natural gas boiler.  (Since we have a ground source heat pump that heats our house and preheats our domestic hot water, the boiler is relatively small and only serves as a back up.  As a result, our gas bill is minimal.)  The boiler needs to ≥ 85 AFUE for the prerequisite; ≥ 87 AFUE for 2 points; and ≥ 90 AFUE for 3 points.   What is AFUE?  The acronym stands for the Annual Fuel Utilization Efficiency.  According to Furnace Compare, “the AFUE is the most widely used measure of a furnace’s heating efficiency. It measures the amount of heat actually delivered to your house compared to the amount of fuel that you must supply to the furnace. Thus, a furnace that has an 80% AFUE rating converts 80% of the fuel that you supply to heat — the other 20% is lost out of the chimney.”  Our boiler is a Buderus Logamax plus GB142, with an AFUE of 96% — again easily exceeding that 3 point threshold.

But we are not yet done with this agonizing credit.  We also have a closed loop ground-source heat pump.  It needs to be ≥ 14.1 EER and ≥ 3.3 COP for the prerequisite; ≥ 15.5 EER and ≥ 3.6 COP for 2 points; and ≥ 17 EER and ≥ 4.0 COP for 4 points.  COP – oh boy – another acronym!  The COP is the Coefficient of Performance, or the ratio of heat output to the unit of supplied input.  In general, ground-source heat pumps are 300%-350% efficient, as opposed to even the most efficient furnaces, which can never exceed 100% (that’s why we are eligible for that 4th point).  We have a Water Furnace E-Series heat pump.  The specifications that came with operating instructions give COPs ranging from a low of 2.93 to a high of 8.98, depending on the temperature of the loop field (under ground) and the temperature required by me, the owner.  So there is not one COP rating for this system.  Since we are not actually going down this path, this predicament does not need to be solved.

I assume we get 3 points for this credit, since the first two sections clearly give us 3.  I won’t take the 4th point for our ground source heat pump because — and this annoys me to no end — our particular model did not qualify us for the 30% federal tax credit.  That leads me to believe that we do not have the most efficient heat pump on the market.  Indeed, I believe our system was oversized.  I believe we over paid for that size, and we will continue to overpay as we use it (not to mention tax credit that would have been in the $12,000 range had we gone down one model in size).  I have learned from this exercise.  Too bad we are not building another house. (Right.)

More commentary on this credit.  We decided to do in-floor radiant heat as the primary method of heating our home.  Since we live in Minneapolis, this was important.  Radiant heat is very comfortable and quiet, and is an excellent way to distribute heat throughout the home.  It is also really efficient when used with a ground-source heat pump, because it’s an entirely closed loop hydronic system.  We got no credit for this, nor is it mentioned anywhere in the LEED for Homes manual.  Additionally, there are different methods of installing in-floor heat.  We used Warmboard (as shown in the photo), which is pre-made with grooves for the pipes to snugly fit, so the flooring can go directly over the warmboard.  Warmboard also has layers of aluminum, which help distribute the heat more evenly across the floor.  Again, no mention of this anywhere.   I think these types of thing should be included in space heating and cooling, because it does make a difference in energy use and comfort.

EA Prescriptive Path points so far: 9