The depreciation of engineering equipment and appliances appears to follow equally well the same general principles as apply to other elements in building construction, but in a markedly increased ratio.
Where its costs bear any large relation to the total cost of a building, the inclusion of an elaborate system of piping, and especially of machinery, adversely affects and reduces the total life of the combined structure, a fact to which very little observation has heretofore been directed. The effects of the interrelation of metallic apparatus with other parts of the structure are generally similar to those already discussed, but are increased by the more perishable class of the materials employed, by their more active character, and by the mechanical movements, and the thermal, electrical, and chemical effects, which they introduce into the structure.
It therefore follows that their character not only affects the general average of their own existence, but detracts appreciably from that of the building.
Throughout modern structures, miles of buried piping lie beneath other materials, which would have to be destroyed if it should at some period be necessary to renew or replace the piping, and thus these materials are affected and their life limited by the piping they conceal.
Decorative features, including trim of all kinds, are affected by what supports them, and thereby affect the permanency of the support. Tile, terrazza, and cement floor surfaces, which have little or no expansive capacity, are laid on steel-framed supports, which are capable of expansion. One portion of a modern building may be overheated by flues, by pipes or radiators, while another part is cold.
After a building is completed, the framing is heated to 70 °, while the exterior may be zero. The interior, therefore, may rise, and expand sidewise, while the exterior is contracting in both directions, by which process the building face is minutely cracked, either in the joints or in the material.
In mechanical appliances a new feature has been imported into buildings which, bearing no inconsiderable relation to the total cost, is of fragile, impermanent character. We do not know the length of life of some of the parts of the equipment of buildings, but we are aware of the fact that much of it is subject to conditions tending toward a perishable character, due to the very services it performs. Sanitary equipment has immensely increased in extent and expense, yet less than a quarter of a century has brought about radical changes in methods, and has demonstrated the perishability of some materials, which were at one time thought to be of the very highest type of permanency.
•Mechanical equipments may be considered in two parts - fixed and motive. Fixed equipments are largely in the form of piping, for a variety of services of more or less importance, affording the means of usage of electrical, steam, sanitary, water, gas, air, and vacuum appliances. Most such systems are liable to become superannuated at an early period, being subject to the course of progressive invention and improvement, requiring their modification or alteration in order to secure efficient results. Such changes are, however, very difficult of attainment, involving serious expenditures and disturbance of the structure, not only on account of the amount, but of the general inaccessibility of piping.
The ramifications of such systems may be illustrated by those installed by the writer in a large apartment-hotel, the extent of which is, in miles, as follows: -
Electric . . . . .
Flues and ducts . . .
Total miles . . .
Even one of the minor elements, if disturbed, would affect a considerable portion of the building materials.
Motive appliances are also quite extensively installed in modern buildings, and comprise elevators and engines, ventilating-fans and motors, refrigerating, pumping, and electrical generating machinery. The life of such apparatus is affected largely by the rapidity of its operation, the shocks or variable loads to which it is applied, and also to some extent by the suitability of its proportions to the work to be performed by it.
The greater the effort which is made to secure economy in operation, the greater will be the complexity of appliances; and the trend has been toward a multiplication of engineering apparatus in buildings. These introduce into the structure new features tending toward physical deterioration, by vibration, strain, and temperature. In electrical apparatus, not only have materials, frail in themselves, been introduced, but a new element aiding the processes of decay has been developed in electrolysis. Apparatus such as the elevator, imposes new and irregular strains on the structure, and power machinery introduces vibrations, while boiler plants and flues increase the effects of expansion and contraction.
Life of most durable part, 40 years
I. FIXED EQUIPMENT
Most durable elements - steel construction, foundations, elevator guides, and overhead framing.....
Exterior framing, copper-cased housings, etc., heating pipe systems used part of the year, gas piping . . .
Buries vents and ducts when painted
Steel-plate stacks and smoke-ducts, cold-water piping, electric conduits
Heating-boilers used part of year
Roof-tanks, sanitary piping systems
Pressure steam piping and appliances.......
Interior drums and tanks, hot-water and pneumatic piping ..................
Exposed and unpainted vents and ducts
Highest-class pressure steam-boilers
Sanitary fixtures, refrigerating piping, kitchen fixtures, and valves
Drip and drain piping, cheaper class of pressure steamboilers
Electric switches, wiring, and connections
Exhaust heads, exposed galvanized ironwork, hot-water drums
II. MOTIVE APPLIANCES
Slowest-speed apparatus, apparatus intermittently used
Dumb-waiters, switchboards, elevator gates, slow-speed elevator engines, shafting and bearings, slow-geared apparatus, elevators intermittently used
Motor-driven pumps, compressors, and moderate-speed fans
Slow-speed reciprocating apparatus, such as pumps, elevator reversing gear, platform lifts
Elevators in regular use, laundry, kitchen, refrigerating, electric devices, and other apparatus frequently reversed
Moderate-speed reciprocating engines, medium-speed rotary apparatus, dynamos and motors
Fan engines, high-speed rotary apparatus on large variations of loads, dynamos, motors, high-pressure engines, condensers
High-speed, high-pressure, reciprocating engines and machines on extreme variable loads
These and many other considerations all point to the necessity for equal conservatism in assuming a life for those less durable features which affect the life of the more durable elements.
Proceeding along such lines, we may reasonably conclude that the life to be assigned to the mechanical appliances in buildings may be classified as shown in Table F.
The mechanical elements in a building may be related to the life of the building materials, and their depreciation combined therewith; but as the life of mechanical apparatus is relatively shorter, it would appear to be the best course to work out its rate of depreciation independently, and assign a special fund to cover it.
The fixed and motive equipments of a large apartment building bear relations which are plotted on Fig. 13, and very interestingly indicate the same general form in the resulting curve as in the case of building materials.