The Passive House in the Electricity System of the Future

In the coming decade, it’s estimated that the world’s use of electrical energy will increase by 34% and by 50% by 2030. Investing in smart grids will help to ensure a quality of supply by interconnecting suppliers and consumers via a two-way digital communication network, plus enabling operators to monitor energy usage and cater for changes in demands.

Trying to reduce the energy consumption of houses will help create a more sustainable energy system. However, this will also influence the design of the energy grids in residential areas and seen as energy standards of passive houses are at such a level, it would not be economically viable to invest in more than one energy infrastructure within a residential area.  This then indicates that it is vital for passive houses to be embedded into the local energy distribution grids in order to be considered in the design of theses energy grids. If not this could lead to a major drop in energy use of houses which could impact on the feasibility of investing in an energy distribution grid in the future as well as  the actual operation of the grid. Furthermore this could also affect energy prices for households.

But, the investment in the grid is only partly dependent on the grid capacity as once in place the grid cost is almost independent of the amount of energy distributed. As a grid is practically a fixed cost, when the energy demands per household decreases, the price per kWh increases because grid related costs do not decrease when the demand decreases. So the concept of passive houses needs to be examined on a broader scale rather than the energy demand for individual houses. Another issue is decreases in energy consumption per household possibly will decreases tax revenues so in order to compensate taxes could be increased.    

Is an all-electric (electricity grid) concept best suited for Passive houses??

Well it will not be feasible to invest in two separate energy distribution infrastructures so the grid has to be the obvious choice as they can be combined with off-grid renewable (e.g. wood pellet or solar thermal heating) or on-grid renewable (green power). But the demand peaks for individual households can be much larger than the average demand for residential areas therefore increasing total investment in generation capacity. So, on the basis of things it is not in favour of individual electricity generation and storage systems. Additional instruments to control the grid will be needed e.g. (Smart meters, Electricity Storage, Demand Side Management). Passive houses may have a role to play in this but due to the low energy demands per household, balancing the grid will become more important.

Conclusion

Passive houses may require a more active role to manage and balance grids and because of this they could require extra investments, however, this will need to be done with current crop of houses anyway so it would appear to be a more sustainable option for the future to invest in passive houses. Furthermore,  a key point in relation ot the passive houses is the heat storage could provide an instrument that grid operators possibily might utilise in order to manage grid loads across a energy distribution system.

Underhill ‘The Stealth House’

This extravagant looking Underhill Passive House Project is situated in a very prominent location at the top of a hill in the Cotswolds Area in West Central England. On the 29^th of Jan 2010 the project passed Passive House Certification, and is therefore the first certified domestic Passive House in England. Being dug into the hill to be invisible from the surrounding countryside, it is essentially a stealth house, with absolute minimal visual as well as environmental impact on landscape. The house is entirely glazed to the south, and the rest of it being earth-sheltered and therefore highly insulated creates the perfect passive solar design. The structure of this underground house is entirely concrete, much of which is left exposed internally to exploit the benefits of its thermal mass. It is insulated and waterproofed externally for the same reason.

The extension is joined to the existing old barn which also was partly renovated with the total treated floor area being 358m². The construction method consisted of externally insulated concrete walls, floors and ceilings. All the insulation used in the house came from Dow Building Solutions in England. The external walls are 220mm thick with the underground U-Value being 0.117 W/ (m²K), also containing Fosroc drains with 310mm Perimate DI-A insulation. In relation to above the ground it has a U-value of 0.153 W/ (m²K) with 250mm insulation and Lotusan acrylic render finish. The floor slab is 250mm concrete; screed and resin finish over 250mm Floormate 300-A insulation and a U-Value of 0.146 W/ (m²K). 

The ceiling consisted of a 250mm hollow core concrete slab and screed with 360mm Roofmate SL-A insulation, also some of the earth has the ceiling partially insulated and the U-Value is 0.085 W/ (m²K). The windows installed in the house are Optiwin Alu-2-Wood which had an overall Uw of 0.74 W/ (m²K) and a G-Value of 50%. Optiwn Frostkorken also provided the front door with a U-Value of 0.72 W/ (m²).

Ventilation in the house is produced by a Paul Campus 500DC balanced mechanical ventilation system which is a Passive House heat recovery unit with 83% efficiency and 0.28 Wh /m³ energy consumption. The heating is from a Woodfire F12 wood burning stove with a back boiler, sealed to room air. 2 post heaters (water based) in air supply ducts distribute the heat. For the domestic hot water a Solex solar thermal roof with 40m² collector area was installed with a 2000 litre accumulator tank; in winter via back boiler from wood stove, it will be backed up through the electric immersion heater.

Key figures:
Air tightness:	n50 = 0.22/h; q50 = 0.23m3/(m2h)
Heating demand:	13 kWh/(m²a) according PHPP
Heat load:	9 W/(m²) according PHPP
Primary energy demand:	62 kWh/(m²a) for heating, DHW, electrical consumption for appliances, etc. (according PHPP)

The house is achieving 90% energy savings over that of an average house. Most of the concrete structure is exposed internally and using this thermal mass from the concrete structure alongside highly-durable insulation has resulted in a highly energy efficient building.