Saturday 8 June 2013

Heating Requirements

Whilst visiting the cold UK over the winter I have been getting my head round the winter heating requirements for my proposed earth sheltered, high thermal mass, solar passive house I am proposing to build in Southern Crete. There is nothing like the cold north easterly wind in Northumberland, in January, to focus the mind on the issue winter heating.

My initial thinking, following my early research, led me to conclude that the best solution would be to use a number of wood fired sources of heat to give me the flexibility I needed to meet the varying heating requirements over the course of a year.

Traditional cast iron wood burning stove heating a large space in chilly Northumberland

My proposal therefore is for:

1) a wood fired range for cooking eg. Esse 990, with a back boiler to supplement the solar hot water system, in the kitchen and located at one end of the large (approx. 6m x 12m) open plan cooking/eating/living area;

2) a wood fired masonry stove, located at the other end of the open plan space, to supplement this range cooker  in the coldest months and maintain the high thermal mass fabric of the house at a comfortable temperature;

3) a small wood burning stove in the main bedroom to provide some rapid warmth at the easterly end of the house for exceptionally cold spells of weather.

Esse 990 - courtesy of Esse Engineering Limited

Estimation of heat loss from proposed house.

Engineers have access to complex computer models for estimating heat loss from a dwelling, James Kachadarian in his classic "The Solar Passive House" (1) provides detailed instructions for calculating heat loss and (2) provides a full explanation of heat loss calculations and principles. As a first estimate, for illustrative purposes, I will, however, use a simplified approach.

Akubue Jideofor Anselm quotes in paragraph 4.4 of his paper "Earth Shelters: A Review of Energy Conservation Properties in Earth Sheltered Housing" (3) that "the heat loss in winter from a 135sq.m single level earth sheltered residence is 12,720 BTU/hr compared with 39,927 BTU/hr for a conventional building of the same size".

In my case the total area of the proposed house is 215sq.m. However in order to include a 2m section of non earth sheltered wall in the rear NNW facing wall, to allow for light penetration, natural ventilation, services access (cold and solar heated water, output from PV system, satellite internet feed etc.) and emergency exit, 200sq. m may be regarded as earth sheltered and 15sq.m as conventional. Doing the calculations based on this I arrived at an estimate of, say, 20,000-25,000 BTU/hr for the proposed building.

(1) "The Solar Passive House" - James Kachadarian


(3) "Earth Shelters: A Review of Energy Conservation Properties in Earth Sheltered Housing" - Akubue Jideofor Anselm