Charging the Earth

Description: The intentions for night air charging have been deemed possible but unnecessary. During late March and early April, the heating system operated effectively at night due to favorable air temperatures compared to glycol temperatures, which proved beneficial. With the arrival of summer, several observations have been made: In the morning, the sunboxes do not activate automatically on cloudy days until the heat pump lowers the glycol temperature sufficiently, which conserves pump power. On cooler days, the sunboxes activate when the ground source heat pump (GSHP) demands heat, supporting it during water heating cycles before shutting off shortly after the GSHP returns to standby mode. This operation is efficient. On sunny mornings, the cold sensor reads room temperature (approximately 22°C), prompting the sunboxes to start if the temperature in the sunbox rises to 27°C. The startup process is effectively balanced at a temperature difference of 5°C, ensuring the pump operates only when the heat gained is significant. The energy harvested on sunny days is substantial enough that pursuing minor gains from nighttime air temperatures is unnecessary, although this perspective may change later in the summer based on data logger findings. Nighttime operation only occurs if the GSHP requires immediate heat, negating the need for interseasonal night charging. The earth beneath the house receives between 8-16 kWh per day, dispersing well and avoiding chilling risks. By day's end, the ground temperature remains acceptable and often exceeds morning temperatures. Previously, evening temperatures were around 5.8°C, but now they can reach 12.8°C by evening, with the next morning stabilizing around 11.8°C after heat dispersal. Consequently, the installation of louvres to facilitate air flushing is unnecessary, as airtight boxes enhance daytime performance. The boxes do not overheat; concerns regarding this were addressed by designing the top louvre primarily to mitigate overheating risks. As the boxes heat up, the pump efficiently extracts heat, maintaining air temperatures below 40°C. The only overheating risk arises if the pump malfunctions, but an expansion bottle in the loft accommodates the liquid mass's expansion. There are cooling louvres installed at the top and bottom for maintenance or testing purposes.

A question posed suggests the possibility of integrating an additional air source heat pump to charge the reservoir during summer using off-peak tariff electricity, potentially cooling the house or surrounding areas when temperatures are mild, or utilizing excess hot water from a solar hot water system during the day. The primary objective remains to harness free solar heat for charging the ground, with the pump primarily powered by the photovoltaic roof. For this system, 'off-peak' is defined as midday when the solar roof can supply power to various household appliances without drawing electricity from the grid. The operation of an air source heat pump (air conditioner) would not be economically viable to achieve what can be accomplished at no cost. In hotter climates, a reverse cycle heat pump might have been considered, but the current system is designed solely for heating.

The described system incorporates a series of components that work synergistically to optimize energy efficiency. The integration of photovoltaic panels provides a renewable energy source to power the heat pump, which, in turn, facilitates the transfer of heat to the ground. The sunboxes are strategically designed to maximize heat absorption during sunny days while minimizing heat loss during cooler periods. The use of temperature sensors ensures that the system only operates when conditions are favorable, thereby conserving energy and reducing operational costs.

The heat pump's operation is closely monitored, allowing for real-time adjustments based on temperature readings from both the sunboxes and the ground. This feedback loop ensures that the system remains responsive to environmental changes, optimizing performance throughout varying weather conditions. The incorporation of an expansion bottle serves as a safety feature, preventing potential damage due to thermal expansion of the fluid within the system.

Overall, the described configuration presents a sophisticated approach to energy management, emphasizing the importance of utilizing renewable resources while maintaining operational efficiency and cost-effectiveness. The system's design reflects a commitment to sustainability, leveraging natural heat sources to reduce reliance on conventional energy inputs.I have also realised that my intentions for night air charging are possible, but unnecessary. When heating is going on (late March/early April) the boxes worked at night because air temp was better than glycol temp - that was helpful. Now that it is summer (we hope it stays that way) I have noticed three things: Morning Startup: The sunboxes don`t

start up by themselves on cloudy days, until the heat-pump lowers the glycol sufficiently : good! this is saving pump power and the heat we would get down would not be worth the pump power. On cool days, the boxes come on when GSHP demands, support the GSHP in Realtime while it does a water heating cycle, then they turn off shortly after the GSHP goes back to sleep. This is good! On sunny mornings, the cold sensor is at Room temperature, say 22 C, so they will start up by themselves if the Sunbox temp rises to 27 C.

(Startup is dependent on the temperature difference - I am finding that 5 degrees C is pretty well perfect balanced - ensures that pump is not on for excessive hours, but when it is, the heat being claimed is worth getting. ). Day gains-Night gains: The amount of power we get on sunny days is sooooo much that it`s not necessary to chase after small gains based on night time air temperatures (but I am willing to change my mind later in summer, depending on the datalogger finding.

) Night time action only occurs if the GSHP demands realtime heat. There`s no point in interseasonal night charging. Temperature reversal : The earth below the house is getting 8-16 kWhr per day. This disperses well, so there is no danger of chilling. At the end of a day, the temperature below is quite acceptable, sometimes higher than the morning temp. e. g. before we did this, the evening temperature might be 5. 8 but in the morning it had recovered somewhat. The reverse is happening now. At the end of the day when we put heat down during the day, but draw little up, the temp is high in the evening perhaps 12.

8, but in the morning, this heat has moved outwards and the stable temperature (stable meaning that for 12 hours, no heat in and no heat out), it is about 11. 8. If this is the case, there is no need to have louvres top and bottom to `flush air through` - this was thought essential for summer night time gains.

The daytime performance is better if the boxes are very airtight. The boxes never overheat - I was worried about this, and the top louvre was intended mainly to meet the overheating risk. However, the hotter the boxes get, the quicker the pump pulls heat from the boxes and buries it, keeping the sunbox air temperature below 40 C (about the same as Baghdad in summer, or your blood temperature).

The only overheating risk is if the pump is not working, but in this case there is an expansion bottle in the loft to cope with swelling of the liquid mass. There are cooling louvres top and bottom, in case I stop the pump for maintenance, or try running the GSHP for a week with sunboxes turned off, for testing purposes.

Question: "Hi David - very interested to see what you were doing with sunboxes! Could an additional string to the bow be using an additional air source heat pump to charge the reservoir during summer possibly using off peak tariff electricity (cooling the house when too hot, or the surroundings when temperatures are mild), or using excess hot water from solar hot water system during day. " The essence of our idea is to use the [free] solar heat to charge the earth - and the pump is mostly driven by power from the PhotoVoltaic roof.

So for us, `off peak` is in the middle of the day - when the roof is able to drive many of the appliances in the house and not import any electricity from the grid. We certainly wouldn`t want to expend the running cost of an air source pump (air conditioner) to do what can be done for free.

If we were in a hot climate, we would have considered a reverse cycle heatpump, but ours is for heating only.