General Conclusions
Energy and Environmental Performance
With regards to the overheating problem at the Visitor Centre during summer months, using shading blinds was proven to be the most effective solution, rather than implementing an energy-intensive cooling system or leaving windows and doors open throughout the working day. Not only were the magnitude and duration of high temperatures considerably reduced, but also this dealt with the issue of glaring. At the same time, the increased ventilation rates, controlled by temperature contributed to the alleviation of the overheating problem.
Grid connection and energy export are essential for the following reasons:
- Achieving a ZEB operation for the Visitor Centre without the grid would be very difficult, as the generation of storage technologies is limited and expensive.
- As an off-the-grid building, Visitor Centre would require significantly oversized generation equipment to cover its energy requirements without leading to energy deficits throughout the year.
- Generates significant additional revenues from Feed-in-Tariffs; there are no currently respective incentives for energy storage.
- Contributes to a “greener” grid.
Looking at our findings, it is clear that the best combinations vary based on the perspective they are viewed. Several criteria could be considered in order to follow the best strategy to meet the ZEB target. The priorities of each stakeholder differ, and in turn their final selection. As described, in our project we focused on investigating at first the demand/supply matching rate for each supply combination and then the cost-effectiveness of the selected supply combinations.
The best combinations according to our findings and the criterion considered that achieve both a Site and a Source ZEB are summarized below.
| Best Combinations | |||
|---|---|---|---|
| Site ZEB | Source ZEB | ||
| Selection Criterion | Demand/Supply matching | 18* PVs (4.5 kW) + ASHP |
(18* + 12) PVs (7.5 kW) + WT (2.5 kW) + ASHP |
| Capital Cost | (18* + 6) PVs (6 kW) + Electric Heaters* |
18* PVs (4.5 kW) + WT (6 kW) + Electric Heaters* |
|
| Net Annual Expenses/Revenues | 18* PVs (4.5 kW) + GSHP |
18* PVs (4.5 kW) + WT (6 kW) + Electric Heaters* |
|
| Payback Period | 18* PVs (4.5 kW) + GSHP |
18* PVs (4.5 kW) + WT (6 kW) + Electric Heaters* |
|
Looking at our findings, it is clear that the best combinations according to the demand/supply matching rate and the cost-effectiveness criteria do not coincide. This is mainly attributed to:
- Intermittency of solar and wind energy outputs – weather dependence
- Different tariffs for different technology types
As it can be noticed, the best combinations coincide only for the Net Annual Expenses/Revenues and for the Payback Period criteria, for both the Site and Source ZEB.
Visitor Centre as a Net Zero Energy Building – Site Vs. Source?
Since the Visitor Centre is already a very high performance building in its own right with installed on-site generation technologies, achieving a Net Zero Energy Building was attainable with small enhancements, compared to a common building of the same usage and size.
More specifically, the most efficient ways to make Visitor Centre a Site ZEB were either to simply replace the existing electric heaters with a more energy efficient heating option (ASHP, GSHP and biomass boiler) or to increase the installed capacity of the PV solar from 4.5 to 6 kW.
As expected, balancing the source energy demands of the building required further supply enhancements. Consequently, the capital required for the Visitor Center to be a Source ZEB was 2 to 10 times greater than the respective for a Site ZEB.
On the other hand, as a Zero Source Energy Building, Visitor Centre has remarkably reduced energy imports and in turn lower dependence on electricity price.
It was also found that the annual energy costs were totally covered by payments from funding schemes, particularly when using a heating system eligible for the Non-Domestic RHI. Revenues were considerably higher for a Source ZEB, giving an annual cash benefit of up to £1800, in the case of installing a GSHP.
With regards to the payback periods for these investments, findings showed that they were overall shorter for achieving a Source ZEB than a Site ZEB. Despite exceeding in some cases the average life span of equipment, findings show that installations for specific combinations pay for themselves after a reasonable amount of years, especially when achieving the Source ZEB.