Central heating

Strength increase (because the cellulose fibrils pack more closely). To prevent movement, wood should be dried to the value which is in equilibrium with the humidity where it will be used. In a centrally heated house (20°C, 65% humidity), for example, the equilibrium moisture content is 12%. Wood shows ordinary thermal expansion, of... 

Glass-reinforced grades have widely replaced metals in pumps and other functional parts in washing equipment and central heating systems. In the manufacture of business machine and computer housings structural foam materials have found some use. Mouldings weighing as much as 50 kg have been reported. 

Rigid polyurethane pipe construction - CFCs in this application are being replaced by carbon dioxide/water, HCFC-22, blends of HCFC-22 and -142b, HCFC-141b, and pentanes. Long-term alternatives will include HFCs and carbon dioxide/water. For district central heating pipes, pentane and carbon dioxide/water are the preferred technologies. 

In buildings that are divided into zones with a central heating system, it is common to change the water temperature depending on the outdoor temperature. In this example a function called feed-forward or compensating is used. Figure 9.55 shows how the water temperature changes as a function of the outdoor temperature. 

This third and last section of Approved Document L is not intended to apply to storage and piping systems for commercial and industrial processes. It concerns only the central heating and the domestic hot water supply of all buildings. The standards are presented in three sections for ... 

As an alternative option, the insulation should meet the recommendations of BS 5422 1977. This Standard tabulates thicknesses of insulation too numerous to mention here, according to whether (1) the pipes carry central heating or domestic hot water, (2) the system is heated by gas and oil or solid fuel, (3) the water temperature is 75°C, 100°C or 150°C and (4) the thermal conductivity of the insulant is 0.04, 0.55 or 0.70 W/mK at the appropriate mean temperature. 

Central heating and domestic hot and cold water supplies ... 

Vaporizing 10-40 kW No Kerosene, gas oil <5 On/off Normally blue flame Central heating... 

In de-aerated conditions, for instance in most central heating systems, little if any attack on copper occurs . As far as drinking waters are concerned, copper is not classified as a toxic substance or hazardous to health. To avoid any difficulties due to unpalatability, the maximum continuous copper content should not exceed 10 p.p.m., with a limit of 3 p.p.m. in water after standing overnight in copper pipes. A review of the subject by Grunau makes reference to 394 published papers. 

The solubility of oxygen in water is influenced by several factors but, generally, most waters contain, at equilibrium, about 8mg/kg at 25°C, although supersaturation may increase this considerably. Some indication of the amount of dissolved oxygen relevant in different situations is shown, on the one hand, by the value of 0-1 mg/kg found in central heating systems and, on the other hand, by the value of 0 005 mg/kg specified by most users of large boilers as the upper limit at the economiser inlet (see Section 5.5). 

The total installed capacity of heat pumps will be more than the central heat pump. 

The size of the central heat pump will be smaller when compared to the total installed capacity of heat pumps in the distributed water loop heat pump system. This is because the central heat pump is sized to meet the block load of the entire building. 

Space savings are not expected at the zone level. However space required for mechanical room components may be lower when compared to central heat pump system. 

Space savings arising from the smaller size of boiler and cooling tower is offset by the addition of central heat pump. Use of fan coil units at the zone level is not expected to result in space savings because of larger requirement of air flow arising from lower temperature difference across the heating coil. 

The first cost is expected to be less than a central heat pump system using ground loop. 

Substantial reduction in noise level can be expected in the conditioned spaces by eliminating heat pumps at the zones. However central heat pump may require special attention to reduce the noise level. 

The first cost of this system is expected to be higher than the distributed water loop heat pump system. Addition of a central heat pump and separate piping for hot and cold water should result in higher first cost. 

Lower first cost than the central heat pump systems using ground loop. Disadvantages ... 

---