|
Introduction The House >> Live data >> Efficiency  Monitoring  >> (Web Energy Logger) >> (WEL Store) The Land Wildlife About Us Podcast Info Links (Resources) Books |
|
Construction Pics Foundation Radiant Slab Acid Stain floors Ground Loop Wood Framing Mechanical Equipment Room Monitoring System Exterior Interior |
|
Mission Statement Earth (Sheltering) Sun (Passive Solar) Water (Geothermal) >> Efficiency test |
|
Design Process Timeline Goals Room Guide Concepts Preliminary 3D Model Final Design Download Plan |
|
Energy Mgmt. GREEN HVAC Energy Logger The Weather |
|
Phil's Other Stuff Marsupials GEARS SUGO Resume |
|
||
On Jan 5, 2004, I had the opportunity to repeat a GSHP efficiency test that I'd performed
two month earlier. The specific nature of the test was to see if the hot water
heating efficiency of my geothermal (ground source) heat pump was within manufacturer specified limits.
In my home, all the hot water for the radiant floor, and for domestic uses
(shower, washing etc.) is generated by a single Ground
Source Heat Pump. Since so much of the house's heat comes from this
source, I wanted to make sure I was getting my full money's worth :) Since
a GSHP efficiency depends on the temperature of the water it's delivering, this
page just documents the Domestic Hot Water side, part way through the heating
cycle (when the tank water is at about 100F).
|
I'm using the Water Furnace
Premier Water-to-Water Heat
Pump, model number P034W10NVAASSA. See the table at the right to decode this number. The Storage Tank has an 80 Gallon capacity. Note the identifiers for the 4 ports on the Heat
Pump. |
|
|
Historic Note: When I first performed this test, my analysis of the results indicated that I had several deficiencies in overall system performance. However, over the last 2 months I have established several reasons why this was not the case, and so I'm retesting, and presenting the updated data and analysis here. Reasons for revised Test/Analysis. I have identified the following reasons why I need to re-do the analysis
|
| SOURCE 7.0 GPM Flow rate | SOURCE 9.0 GPM Flow rate | ||||||||||||||
| ELT | EST | LLT | HC | KW | HE | COP | LST | PSI | LLT | HC | KW | HE | COP | LST | PSI |
| 100 | 50 | 110 | 24.3 | 2.33 | 16.3 | 3.1 | 44.5 | 4.6 | 110 | 22.8 | 2.35 | 14.8 | 2.9 | 46.5 | 6.9 |
| 108 | 24.7 | 2.30 | 16.9 | 3.1 | 44.6 | 4.6 | 108 | 25.2 | 2.33 | 17.3 | 3.3 | 46.0 | 6.9 | ||
| 106 | 25.2 | 2.28 | 17.4 | 3.2 | 44.6 | 4.6 | 106 | 27.6 | 2.31 | 19.7 | 3.4 | 45.5 | 6.9 | ||
New Test Procedure.
- I first dropped the storage tank water temperature down to below 100 Degrees F, by running several radiant zones.
- Next, I disabled all equipment except those components required to generate Hot Water. This included disabling the Radiant Floor zone circulators, ERV, Air handler and well pump.
- I then ran the W-W heat pump with all the other HVAC devices disabled.
- I monitored the heat pump's operating variables. This included the electrical load, source water pressure readings & all water temperatures. I recorded these variables at the point when the Entering Source Temperature (EST) was 100 degrees.
Here are the results:
Electrical Load:
| Heat Pump Off | 48 W |
| Heat Pump On | 3502 W |
Water Temperatures:
| EST | 49.6 °F |
| LST | 45.0 °F |
| ELT | 99.9 °F |
| LLT | 106.9 °F |
Water Pressure:
| Entering Source Pressure: | 16.0 psi |
| Leaving Source Pressure: | 10.8 psi |
Analysis:
Electrical Load. This is now easy to determine with the new
watt meter. However, some numbers do need to be subtracted from the
indicated power load. There are two source-side circulator pumps which
each draw 420W (1.75A @ 240V), and a single load side circulator which
draws 84W (0.7A @ 120V). This is also a minimal housekeeping load of
48W from other devices.
For my system, KW = 3502 - 972 = 2530 W.
This is 200W higher than expected, but it's within
reasonable limits.
Heat Extracted: This is an all-important number, it indicates how much
heat is being extracted from the ground loop. This can be calculated based
on the water flow rate and temperature drop across the Source Heat
Exchanger. Flow rate can be determined by measuring the pressure drop
across the heat exchanger and then using lookup tables. My measured
pressure drop was 5.2 psi, which extrapolates to about 7.5 GPM based on the
chart above. Heat extraction can be calculated as GMP * Temp Diff. *
500.
For my system, HE = 7.5 * 4.6 * 500 = 17,250
BTUH. This is well within the expected
range.
Heat Capacity: Water Furnace assumes that in addition to the heat
extracted from the source water loop, the electrical energy consumed by the heat
pump is also converted into heat and fed into the load fluid, so the total Heat
Generated is HE + (KW * 3.413).
For my system, HC = 17,250 + (2530 * 3.413) = 25,884
BTUH. This is well within the expected
range.
Coefficient Of Performance: COP is defined as: Heat Energy
Generated divided by Electrical Energy Consumed. Expressed in BTUH this
would be HC / (KW * 3.413).
For my system, COP = 25,884 / (2530 * 3.413)
= 3.0. A respectable number.
To put this in perspective, it's 3 times better than a baseboard heat, electric
DHW system would be.
So in the final analysis my system seems to be performing at about par with
what should be expected.
My earlier disappointment was due to invalid expectations and poor power
measurements.
|
An exercise in Energy Smart, Not So Big living. www.OurCoolHouse.com - Ideas @OurCoolHouse.com
|
This site is all about building a cool, energy efficient house, that makes maximum use of earth sheltered design, passive solar heating and cooling, geothermal exchange energy management, and right sizing of the house for it's designated use. The home's placement is on a south-facing hillside in Deep Creek Lake, Maryland. This site describes the design process, the technologies used and the expected results. We also have a comprehensive Links Page for anyone who is also interested in designing a similar project.