A
Astro
- Jan 1, 1970
- 0
A few weeks ago, I had a GSHP system installed. Along with the loops, I
installed temperature sensors so that I could monitor the temperature of
the ground at the loops. In this way, I figured that I could monitor
system efficiency during the course of the seasons. This is a four ton,
direct expansion system with four, 100ft vertical loops. The ground here
is solid granite for hundreds of feet down and around. Little to no water
movement.
The measurements I'm making are as follows -
Run the system normally for some period, i.e. a couple of days of
operation. While the system is running, I'm monitoring the vent, room, and
outside temperatures throughout the house. I'm also monitoring the
temperature of the refrigerant lines to/from the compressor unit and have
measured the current draw at the breaker panel.
Next, I turn the system off for a period, typically the better portion of
a day. During this period, I monitor the loop temperature sensors to see
ground temperature recovery.
Finally, I have a monitor buried at roughly the same depth (these are all
vertical loops) so as to provide a ground control temperature.
The results I'm getting are illuminating (and disappointing!)
Control ground temperature started at 51F on 12/8/04. It is now 49.9F on
12/28/04.
Total system run-time during this period has been 150 hours.
The ground around the loops is freezing within <24 hours of system
operation. Along with the loop cooling goes the vent temperatures. When
the system is fresh (i.e. loop temperature recovered to the mid 40's), the
best vent temperature is around 93F. (My ductwork is tight and well
insulated). Maximum vent temperature is within 2F of the temperature
measured right at the air handler.
Ground loop recovery is getting progressively worse as the usage
increases. I assume this is because the ground around the loops is getting
colder. Currently, it takes about 6 hours for the loops to "unfreeze" from
about 30F to 32+F. Then, the loops rise at 1.1F/hour until they reach 38F.
Then they slowly rise a couple degrees above that. Measurements just a
week ago showed loops rising up to a about 42F before leveling off to
about 45F. My suspicion is that within a couple more weeks of use the
loops won't even rise above freezing.
My computed BTU output for the system runs from 32000BTUs/hr to
42000BTUs/hr. This system is rated at 4 tons, and I was told that it
typically puts out closer to 5 tons at the start of the season and it
drops to about 40000BTU by the end of the season as the ground cools.
The system was "professionally installed". The installer came highly
recommended by the manufacturer.
On the initial install, the loops were backfilled incorrectly resulting in
the tubing making minimal contact with the surrounding ground. These
measurments are from after I corrected this problem.
The system was supposed to have six loops, 100ft but the drill rig broke
during installation. However, the manufacturer states that four, 100ft
loops should be sufficient.
The loops were supposed to be installed at least 10ft apart but they are
6ft apart.
After doing many hours of research, I feel that there are several issues
here.
First, the thermal diffusivity of the ground is such that much more ground
loop is needed to balance the thermal load being placed on it. I have
typically read that about 250ft/ton is required for conventional gshp
systems and under good conditions, this can drop to 200ft/ton for a direct
expansion sysetm. so from the getgo, I'm at least 50% of the desired loop
size.
Second, the loops are too close together. At 6ft apart, the BTU capacity
of the surrounding ground is seriously compromised. Most of what I've read
suggests that 225 sq. ft/loop is required for long term ground temperature
stability. This is running at 16% of this.
The manufacturer stated that even 8ft loop separation is within spec.
Ok, now besides telling me that I've been ripped off, I'm interested in
other peoples experiences with GSHPs. Has anybody besides me taken the
time to actually quantify the performance of their GSHP system? I've read
everything on the standard GSHP sites and none of what I've seen actually
shows what expected ground loop temperature is in the immediate vicinity
of the loops. I've read about the overall ground temperature of the loop
field, but haven't encountered any literature discussing what I'm
measuring.
I've also seen measurements of water loop systems, where the water
temperature to/from the ground loop is measured. This would be a good
indication of the loop field temperature. Anybody have numbers from their
systems?
I am now investigating remediation for the system. I am considering two
options:
1) Install 6 additional vertical loops, spaced 15ft apart from one
another. this would give the required 225 sq. ft/loop and would increase
the system to 250ft/ton.
2) go to a horizontal loop field since drilling here is so damned hard and
expensive.
Any suggestions on an effective, long term remediation would be greatly
appreciated. Spare me the snide remarks about installing a gas burner and
throwing away the GSHP. I actually have a working baseboard hot water
system that this system is supposed to replace. Now I'm alternating
between the systems to save oil.
installed temperature sensors so that I could monitor the temperature of
the ground at the loops. In this way, I figured that I could monitor
system efficiency during the course of the seasons. This is a four ton,
direct expansion system with four, 100ft vertical loops. The ground here
is solid granite for hundreds of feet down and around. Little to no water
movement.
The measurements I'm making are as follows -
Run the system normally for some period, i.e. a couple of days of
operation. While the system is running, I'm monitoring the vent, room, and
outside temperatures throughout the house. I'm also monitoring the
temperature of the refrigerant lines to/from the compressor unit and have
measured the current draw at the breaker panel.
Next, I turn the system off for a period, typically the better portion of
a day. During this period, I monitor the loop temperature sensors to see
ground temperature recovery.
Finally, I have a monitor buried at roughly the same depth (these are all
vertical loops) so as to provide a ground control temperature.
The results I'm getting are illuminating (and disappointing!)
Control ground temperature started at 51F on 12/8/04. It is now 49.9F on
12/28/04.
Total system run-time during this period has been 150 hours.
The ground around the loops is freezing within <24 hours of system
operation. Along with the loop cooling goes the vent temperatures. When
the system is fresh (i.e. loop temperature recovered to the mid 40's), the
best vent temperature is around 93F. (My ductwork is tight and well
insulated). Maximum vent temperature is within 2F of the temperature
measured right at the air handler.
Ground loop recovery is getting progressively worse as the usage
increases. I assume this is because the ground around the loops is getting
colder. Currently, it takes about 6 hours for the loops to "unfreeze" from
about 30F to 32+F. Then, the loops rise at 1.1F/hour until they reach 38F.
Then they slowly rise a couple degrees above that. Measurements just a
week ago showed loops rising up to a about 42F before leveling off to
about 45F. My suspicion is that within a couple more weeks of use the
loops won't even rise above freezing.
My computed BTU output for the system runs from 32000BTUs/hr to
42000BTUs/hr. This system is rated at 4 tons, and I was told that it
typically puts out closer to 5 tons at the start of the season and it
drops to about 40000BTU by the end of the season as the ground cools.
The system was "professionally installed". The installer came highly
recommended by the manufacturer.
On the initial install, the loops were backfilled incorrectly resulting in
the tubing making minimal contact with the surrounding ground. These
measurments are from after I corrected this problem.
The system was supposed to have six loops, 100ft but the drill rig broke
during installation. However, the manufacturer states that four, 100ft
loops should be sufficient.
The loops were supposed to be installed at least 10ft apart but they are
6ft apart.
After doing many hours of research, I feel that there are several issues
here.
First, the thermal diffusivity of the ground is such that much more ground
loop is needed to balance the thermal load being placed on it. I have
typically read that about 250ft/ton is required for conventional gshp
systems and under good conditions, this can drop to 200ft/ton for a direct
expansion sysetm. so from the getgo, I'm at least 50% of the desired loop
size.
Second, the loops are too close together. At 6ft apart, the BTU capacity
of the surrounding ground is seriously compromised. Most of what I've read
suggests that 225 sq. ft/loop is required for long term ground temperature
stability. This is running at 16% of this.
The manufacturer stated that even 8ft loop separation is within spec.
Ok, now besides telling me that I've been ripped off, I'm interested in
other peoples experiences with GSHPs. Has anybody besides me taken the
time to actually quantify the performance of their GSHP system? I've read
everything on the standard GSHP sites and none of what I've seen actually
shows what expected ground loop temperature is in the immediate vicinity
of the loops. I've read about the overall ground temperature of the loop
field, but haven't encountered any literature discussing what I'm
measuring.
I've also seen measurements of water loop systems, where the water
temperature to/from the ground loop is measured. This would be a good
indication of the loop field temperature. Anybody have numbers from their
systems?
I am now investigating remediation for the system. I am considering two
options:
1) Install 6 additional vertical loops, spaced 15ft apart from one
another. this would give the required 225 sq. ft/loop and would increase
the system to 250ft/ton.
2) go to a horizontal loop field since drilling here is so damned hard and
expensive.
Any suggestions on an effective, long term remediation would be greatly
appreciated. Spare me the snide remarks about installing a gas burner and
throwing away the GSHP. I actually have a working baseboard hot water
system that this system is supposed to replace. Now I'm alternating
between the systems to save oil.