On reflection it would have been a sensible idea to run some good-quality coaxial cable from the comms room to the likely locations of TVs around the house. While video transmission is definitely moving towards Internet streaming services you still get a more seamless viewing experience when you can provide a TV with a good aerial signal.
In particular, it was surprising to find that the ‘All 4’ catch-up app on Android TV needed to be enabled via the YouView setup process – which insists on seeing an aerial, albeit only temporarily.
There are two CAT6 cables running from the comms room to all the likely TV locations, so one of those provides a wired Internet connection and there’s a second one available for other purposes.
While the high frequencies of broadcast television present something of a challenge, using a pair of high quality baluns it’s perfectly feasible to distribute a TV aerial signal over 50 or so metres of CAT6 cable. MuxLab from Canada offer a range of baluns and their CATV units are rated up to 900MHz. They offer shielded and unshielded variants. In the UK they’re available from CPC Farnell and other similar distributors.
It’s pretty much essential to use an amplifier to help offset the inevitable loss of signal strength. This one from Labgear works well.
This post is a follow-on from Part 1 which reported the experiences at the start of the heating season (at the end of November). After a few months of rather colder temperatures and the extraction of a considerable amount of heat from the ground, the Coefficient of Performance figures are still good but somewhat less impressive than before.
It’s evident that the temperature of the water coming in from the ground loop has a significant effect on the efficiency of the heat pump and the heat output it is able to deliver. At the end of November the ‘brine’ was typically coming in at 10 degrees whereas now it’s around 5 degrees. With brine at 10 degrees, the 8 kW heat pump was actually delivering 10 kW (as reported by the Kamstrup heat meter) whereas with brine at 5 degrees it’s ‘only’ delivering 8.5 kW. The heat pump experts tell me this is expected behaviour and it’s why an ‘open loop’ heat pump taking water from a lake or river performs better than a ‘closed loop’ unit which circulates the same brine around a closed circuit.
The headline performance statistics are now:
In ‘heating’ mode, the unit is delivering an instantaneous CoP of around 4.25
In ‘hot water’ mode, the unit is delivering an instantaneous CoP of as little as 2.75
In ‘heating’ mode the heat pump attempts to match the heat loss from the house by delivering water into the heating circuits at just the right average temperature. With colder temperatures outside this equates to warmer water, which tends to equate to lower efficiency (although actually the high thermal mass of the house reduces the impact of brief cold spells). During a typical ‘run’ it is still consuming almost exactly 2 kW (just like in November) but delivering 8.5 kW, for a CoP of around 4.25.
On cold-but-bright days, the hot water gets heated by the Immersun unit that diverts excess solar PV generation to the immersion heater, which has its thermostat set to 60 degrees. (It does this often enough that I’ve switched off the heat pump’s own anti-legionella sterilization cycle for the hot water tank.) On dull days the heat pump still kicks in to heat the stored hot water to 50 degrees. With the lower brine temperature (5 degrees in, 0 degrees out) it still consumes up to 2.88 kW but wth a reduced power output of 8.0 kW, for a CoP of 2.77.
The first set of graphs below are from a sample 24-hour period (2018-02-15T20:00 to 2018-02-16T20:00) which show:
Some of the heat pump temperatures, as reported by its internal control system
The heat pump power consumption, as reported by the sub-meter on its electricity input
The heat pump power output, as reported by the heat meter on the ‘heating’ flow pipe from the heat pump
These graphs also show the ‘cycling’ of the heat pump:
Overnight, it ran for 20 minutes every 1 – 2 hours
From 11:00 – 18:00 it shut down completely
This is because it was a cold but bright day: 0 degrees at 07:30 but then warming to 5 degrees by 11:30 and on to 7 degrees for much of the afternoon
As the outside temperature rose, the ‘Calculated’ (target) temperature for the heating circuit was reduced
Also, once the sun made it onto the polished concrete floor slab containing the UFH pipes the UFH stopped calling for heat
There are floor probes in the concrete slab which control valves on the UFH pipe loops to maintain the temperature of the slab at 23 degrees
GSHP Performance Graphs for a cold but bright day in February
The second set of graphs (below) show a ‘hot water’ cycle starting at around 2018-02-15T05:00. Note how the increased water delivery temperature (peaking at 55 degrees) corresponds to an increased electricity consumption (peaking at 2.88 kW) while the power output remains steady at 8.0 kW.
GSHP Performance Graphs for a hot water heating cycle in February