where q is heat flux, W, k is heat transmission coefficient
, W/([m.sup.2] x K), A is heat exchange area, [m.sup.2], and [DELTA][T.sub.m] is average temperature difference, K.
Under the Lithuanian climatic conditions, the air heating system will operate efficiently if heat transmission coefficient
does not exceed 0.12 W/[m.sup.2]K and 0.85 W/[m.sup.2]K for non-transparent and transparent envelopes respectively, air exchange in the building is within the limit of 0.05 1/h, linear thermal bridges are allowed only through window and door reveals and do not exceed 0.05 W/mK, and finally, heat recovery efficiency of the mechanical ventilation equipment is no less than 80%.
Envelope heat transmission coefficient of each alternative Heat transmission coefficients, W/([m.sup.2] x K) / Alternatives Envelope Existing Unorm & U25 & U50 & type situation Unorm+Bio U25+Bio U50+Bio Walls 1.10 0.28 0.20 0.14 Roof 1.10 0.21 0.17 0.11 Windows 2.56 1.82 1.36 0.90 Doors 2.30 1.80 1.35 0.90 Floor 0.64 0.22 0.17 0.11 Table 2.
The values of heat transmission coefficients of the envelopes of each alternative are presented in Table 1.
where [c.sub.0] [W [K.sup.-1]], [c.sub.1] [W [K.sup.-1] [V.sup.-1]], [c.sub.2] are weighting coefficients for the estimation of the overall heat transmission coefficient
of the cooler, [K.sub.c](t) [W [K.sub.-1]] is the overall heat transmission coefficient
of the cooler, [M.sub.c] [kg] is the overall mass of a fluid in the cooler, [u.sub.c](t) [V] is a voltage input to the cooling fan, [[tau].sub.c] [s] is a delay of a fluid flow through the cooler, [[tau].sub.KC] [s] is a delay between a control signal to the cooling fan and the output temperature of the cooler.
Transmission heat loss per square foot, caused by the heat conductivity of building material, is measured by the heat transmission coefficient
, U, the number of Btus transmitted through one square foot of surface of a particular material for one degree of temperature difference between one side of the material and the other, T, over one hour.
the Fourier equation for the mono-dimensional heat conduction can be solved thanks to the properties of the [e.sup.[j[omega][tau]]] operator, and the heat transmission coefficients
of the generic slab of a multilayered wall can be evaluated (Carslaw and Jaeger 1960):
Based on the input calculations, for each structural part of the building the heat transmission coefficients