RESULTS HEATING TRIALS
As I studied the first set of results, the numbers didn't make sense. I appeared to have 'lost' 15kw of heat into the floor! An investigation showed that the boiler, which I got 'nearly new', had had a smaller jet fitted, and has a far lower output than the maker's plate implies.
Makers data: Burner output, 0.5gph jet with preheater, 12 bar pump, diesel fuel,
18.4kw gross, 16.5kw net.
Estimated transmission losses allow 1.0 kw
Net output to floor(s)= 15.5kw = 53000btu/hr
Water/ethylene glycol, 33%, btu/lb/degF= 0.92
specific gravity = 1.04, taken as near enough 1.0
Ambient t during trials = 19C(66F), and to avoid math complications, all ambient temperature readings were adjusted to 19C as they varied during the trials.
All thermometers were calibrated with an electronic medical thermometer.
C= centigrade scale, K= degrees Centigrade, F = Fahrenheit scale, dF = degrees Fahrenheit.
Results
Second (first Europe) floor trial.
Foil/bubblewrap insulation layer over 7/8" t&g softwood ceiling, ( so we could walk on it laying pipes), under 15mm OD/11mm ID X-linked polythene pipes laid as 3 discrete loops of 100 metres (328ft.) at 200mm (8") centers, fed from 22mm OD copper pipe/ manifolds. Floor 1" t&g cedar of lebanon boards. There is a 1" airspace over the pipe, and the floor is sealed at edges to prevent convection currents. This is a low wattage emission design.
Boiler trial #1
t'stat set 57C-65C. Mean= 61C; range 8K, (14.4dF)
time burning= 1645 sec. (about 2mins 30sec per burn).
time off= 5960 sec
total time= 7605 seconds
Burn time= 22%
THEORY
22% burn, 15.5kw net= 3.41kw to floor, but allowing 400W loss to the room below;
To floor = 3.0kw on 72 m2 = 41.7W/m2
Using the well known emission coefficient of 11W/m2K (3.5btu/hr/sq ft./dF) -
Floor temperature should be 3.8K ( 6.8dF) over ambient.
PRACTICAL RESULTS
Flow into 2nd floor @ 40C (104F). Return from floor 35C (95F) Range 5K (9dF)
Find the exact flow rate through the floor, without instruments!!
Boiler shell holds 14 litres (30lb) and cycles approx. 9 minutes off, 2.5 minutes firing. 30lb falls 14.4dF = 30x14.4x0.92= 394btu drop between firings. Water returning to boiler drops 9dF losing 9x0.92= 8.28 btu/lb of flow.
In 9 minutes, return water cools boiler at 397/9 = 44btu/min..
So flow must be 44/8.28 = 5.3 lb/minute or 0.04 litres / second.
Now the mix valve takes in water, (from thermometer reading) at 55C (131F), so 1lb at 55C + 3lb at 35C = 4lb at 40C. Flow through the floor = 4 x 0.04
Flow = 0.16 litres/second, 3.52 lb/second
0.16 litres/sec = 1267lb/hr x9dFx 0.92= 10491 btu/hr= 3.06kw, and in a 72m2 floor output is 42.6W/m2 ( 13.3btu/hr/sq ft)
Using 11W/m2K, floor temperature should be 3.87K, 7dF above ambient.
Floor temperature measured at 22.5C @19C = 3.5k ( 6.3dF)
Estimated actual power = 42.6W/m2= 3kw, ( 10,489btu/hr) at the second floor.
First (ground) floor trial.
Base layers plus 50mm extruded PS foam under 75mm dense concrete floating floor slab. Pipe layour as per second floor, except there are 4 x 100 metre loops. Cover over pipes 50mm. Weight 12.4 imp. tons, floor will have a ceramic tile finish.
Edges of floor have a thermal break.
Area heated, 84m2 (904 sq ft).
At 28C mean slab temp., from a 20C start, slab requires 14.4x0.2x12.4x2240= 80,000 btu or 23.5kwh to raise to working temperature.
Boiler trial.
The required power of this floor is only 50W/m2, bearing in mind the insulation and venting design. Circulators can only deliver a fixed quantity of heat, and this is less than the boiler output. A stable condition was never reached, I still have no room stats (French supplier!), so trial was terminated once 50W/m2 was achieved. A boiler trial is thus pointless. This meant a flow rate could not be calculated, so I will assume it is about 0.16 litres per second.
Floor cover of 50mm concrete will drop temperature from the water by;-
R=p/y; y=1.1W/mK, p=0.05m, so R=0.45W/m2K
t drop thro' concrete, y/R = 2.4K, so mean water temperature required is 28C, 82F
From this figure, floor requires 3.8kw plus an allowance for losses into the earth.
Downward heat loss to earth is not math for the faint hearted! So I used tables!
50mm of EPS in a concrete floor of this size, 1/R= 0.5W/m2K , at 28C loss = 1175W
So total power required = 5kw, 17000btu/hr.
If flow is 0.16 litres/second, similar to upper floor, = 1267lb/hr at 1165btu/dF, the temperature drop should be 14.4dF at 17000btu/hour, and exit water should be 35C or above.
TRIAL DATA
Time to reach approx. 50W/m2 from 19C start, = 5 hours 11 minutes
Floor temperature was 24C(75F) = 5K (9dF) rise, at trial end.
Input water 43C (109F)
Return water 35C (95F) at trial end.
8K achieved = 50W/m2 approx.
TRIAL STOPPED.
Phew!
Alan
ps. I reasoned that at an ambient temperature of around 19C, the emissions from the floors would be roughly the same as if all the insulation had been installed. A lucky break in the weather.
Edits for spelling and typos.
Edit, decimal place error.
{Message edited to remove edit notices}
[This message has been edited by Trumpy (edited 03-24-2006).]
