Building Envelope Design and Cooling Load

This assignment delves into the concept of building envelope design and its impact on cooling loads. It provides a framework for calculating cooling loads based on factors like wall area, window size, and roof construction. The document emphasizes the use of 'design equivalent temperature difference' to determine heat transfer rates through various building components. Students are tasked with applying these concepts to a hypothetical building scenario, demonstrating their understanding of building performance analysis.

How to improve the HVAC system of the building
Among the tips that can be adopted by the hotel to achieve an efficient HVAC system include;
Installation of n economizer: This is one of the simplest and lowest-cost solutions that would
enhance the HVAC performance of the building. Through an economizer, mechanical cooling
would be replaced by passive cooling in which the economizer lets in the cooler temperatures
outside the building into the building (Liu 2013, p. 398). In so doing, the compressor as a
mechanism of powering air is eliminated and the only energy requirement in the building is to
move the air throughout the hotel. The air inside the building tends to be hotter than that outside
the building due to the overproduction of energy and heat during operational hours.
Reducing load capacity: load capacity is basically the cumulative cooling and heating used in a
building and an increase in the load capacity negatively affects the running of existing systems.
Some of the strategies of reducing the load capacity of the hotel would be;
Installation of insulators
Such opening s as in the roofs, walls, pipes and ducts are a very integral part in the management
of the energy performance of a building (Gupton 2012, p. 897). The tear and wear of these
components of a building in most cases culminate in cracks and holes that permit escape of heat
from the building.
Installation of window films
This aims at enhancing energy performance by keeping check of the heat from the solar that
accesses the building from the window openings. It is estimated that up to 30% of the solar heat

gain in a building is through windows (Blum 2016, p. 166). By using window films, up to 80%
of such gains is absorbed and reflected back to outside the building.
Upgrading the building to energy star certified office equipment
Just like lighting, old office equipment tend to generate as much heat hence the need to upgrade
to better energy efficient equipment. Such equipment as energy star certified equipment is better
ways of enhancing the energy performance thereby reducing the load capacity of the building.
Maintenance of HVAC system
To ensure the HVAC system is running as efficiently as possible, proper maintenance should be
given a center stage (Gupton 2012, p. 288). The maintenance practice includes but is not limited
to checking and tuning up the system before the beginning of every winter season. Checking for
defective equipment and leaks in the coils, ducts, pipes and unit fittings so as to ascertain any
anomalies and the most appropriate corrective measure adopted is as well as maintenance
strategy. Just like any other equipment, boilers, chillers and other cooling and heating equipment
also tear and wear with time and would thus require replacements. Heat transfer can be
compromised in case there is accumulation of cleaning debris and dust in the ducts and coils in
the HVAC system hence should frequently be removed (Smith 2009, p. 458).
Another way of maintaining the HVAC system is by regular change of the filters most
appropriately after every month.
Educating the workforce
The need to conserve energy touches directly on the bottom line of the hotel owner or the
manager and this may not be to the knowledge of the employees of the facility. For this light, it

is important that the employees are trained on the strategies that would enhance the efficiency of
the building (Liu 2013, p. 189). The facility management may consider organizing a brief
training for its workforce so as to impart in them such skills that would ensure best energy
efficiency practices that would see the load capacity of the facility reduced.
Scheduling a professional energy edit
An audit of the HVAC system of the hotel would be important in enhancing upgrades of energy
efficiency. The audit should be consistent with the age and parts of the system as well as the
current condition of the unit. From the professional audit, simple fixes can be made without
necessarily making new purchases.
Purchasing a new HVAC system
This would be the last option and should be done upon inspection and finding out that the system
may need a replacement in order to work better (Krarti 2016, p. 697). This is through a check of
the system’s Seasonal Energy Efficiency Ratio rating. If the rating is found to be less than 13,
then an upgrade would be recommended.
Implementation of controls
Preferences on how cooling and heating systems function can be set by the user of a space using
controls in a way that they are running more efficiently behind the scenes. Demand and
occupancy sensors, programmable thermostats and timing automation systems among other
devices are among the devices that can be used as controls (Rutkowski 2011, p. 396). These
devices utilize cooling and heating during busy hours as when as when the building is non-
operational.

Type of HVAC System used
The type of HVAC system used in the hotel is split HVAC system. The various components of
the system are located both to the inside and outside of the hotel building. Among the
components of the system include air conditioning units, thermostat, ducts and evaporator coils.
The outdoor unit of the system which is composed of the compressor, expansion coil, capillary
tuning and condenser coil is installed near or on the external wall of the building. The indoor unit
is made of a filter, cooling coil and a blower (Coffin 2012, p. 429).
The system might have been adopted due to the following reasons;
Its quiet performance: The components of a conditioner which produce sound are the fans and
the compressor which cool the condenser. These components are located outside the building
hence minimizing the levels of noise. By locating these components outside the building, the
comfort levels of the hotel are increased. Location of the compressor and the fans outside
eliminates the major noise sources in the room.
It is efficient and cost effective: In as much as the initial cost of the installation of split HVAC
system could be higher than that of a window unit, this system saves on energy hence relieving
the facility owner significant energy bills as well as the durability of the system (Bondanza
20111, p. 354). Upon professional installation, the split HVAC system makes it worth a while in
the long run.

Possibility of a multi-split system: Split HVAC system gives the user an opportunity of having
more than a single indoor unit connected to one outdoor unit. In so doing, it is possible to cool
numerous rooms simultaneously without necessarily bring in a different system set. This saves
on cost as well as helpful in maintaining the indoor temperature of the larger rooms by use of just
one outdoor unit. Under circumstances as when the hotel management may opt to expand the
size of their premise it may not need to go for a completely new system but instead just adjusting
the existing one.
An alternative system the hotel may adopt is Heating and Air Cooling System in a Single
Package. This system is most appropriate in cases where there is limitation of space that can be
used in the accommodation of all the components of the split system. In this system, all the units
are confined in a single system (Blum 2016, p. 255). It is composed of an air conditioner fitted
with an evaporator and a control system that is equipped with a thermostat.
Packaged Air Condensers come in two categories: one with air cooled condenser and another
with water cooled condenser. Among the advantages that come along with this HVAC system
include;
 Low levels of indoor noise: Just like the split system, the noise levels in packaged air
cooling and heating conditioners are relatively low especially if the packaged unit is
maintained in good conditions.
 Possibility of maintenance in one place since all the components is at one place
 The most important advantage that comes with this system is the saving both on space
and money hence very ideal for extreme climatic conditions (Brumbaugh 2012, p. 566).

On another hand, high chances of damage and their location on the roof tops pose a threat to
their usability and thus efficiency.
Cooling Load Calculations
Cooling loads are a resultant of process of heat transfers that take place through the building
envelope as well as those from internal system components and sources. it should be
remembered that a building is composed of external components among them walls, windows,
floors, roofs, ceilings and partitions. It is also composed of internal components among them
occupants, equipment, light and appliances besides infiltration including migration of moisture
and air leakage (Hartman 2013, p. 231). Heat gains are classified by the mode by which it enters
into space as whether it is latent or sensible. Whereas sensible heat is added directly into a
conditioned space either through radiation, conduction and/or convection, latent heat gains are as
a result of addition of humidity into a space.
Heat Gain through Exterior Surfaces: occurs mainly through solar radiation. Heat flow into
exterior surfaces which are sunlit is given by the equation
Q
A =∝ Et +ho ( to−ts ) −ε ∆ R
where
∝−surface absorptance for solar radiation
Et −total surface radiationincident on surface
ho−coefficient heat transfer by longwave radiation
to−outdoor air temperature

ts−surface temperature
ε −surface hemispherical emittance
∆ R−long wave radiation difference
Heat transfer rate can be expressed as
Q
A =∝ Et +ho ( to−ts )
And from the above equations, the sol-air temperature is
te=to+ ∝ Et
ho
− ε ∆ R
ho
Total fenestration heat gain
Q=Qdir+Qdiff +Qcondactive
The various parts of fenestration heat gain include;
Direct solar heat gain which is estimated from the equation;
Qdir= A . Edir . SHGC ( θ ) . IAC
Diffuse solar heat gain
Qdiff = A . ¿ ¿
Conductive heat gain

Qc=U . A .(to−t1)
Heat gain through interior surfaces
The rate of transfer of heat is given by
Q=U . A .(tb−t1)
Internal heat gains: these gains are as a result of such factors as the occupants, lighting and
appliances among other factors. in different states of activity, the occupants of a room lost both
heat and moisture. The load on this factor is mostly experienced either as sensible or latent heart
gains.
Instantaneous heat gains from lighting is determined by
Qe 1=W . Ful +Fsa
where
Qe 1−heat gainresulting ¿ electric lightin g
W-total watts of light
Ful−lightinguse facto r
Fsa−lighting special allowance facto r
Example calculation on cooling load calculation
Determine Building Envelope Areas (SF)
Building: 200’ x 100’ (2 stories, 12’-6” each)

N E S W
Gross Wall 5,000 2,500 5,000 2,500
Windows 1,000 500 2,000 500
Doors 20 20 50 20
Net Wall 3,980 1,980 2,950 1,980
Roof/Floor Slab 20,000
Determining design equivalent temperature difference;
Using the table below as the guide and the following properties of the materials of the building

Roof Construction type: Light color, vented, ceiling, the design equivalent temperatures would
be
Design temperature: 95ºF
Mean daily range: 32ºF
L: 0-16ºF
M: 16-25ºF
H: 25+ºF
DETD=31.0ºF
The cooling load calculations using the provided design equivalent temperature difference
would be calculated by filling the table below as shown for the various properties of the material.

The same calculation can be done for the various on other components of the building envelope
and the different transmission routes of heat in and around the building.

References
Blum, DH 2016, Improving the Use of Commercial Building HVAC Systems for Electric Grid
Ancillary Services, 3rd edn, Massachusetts Institute of Technology. Department of Architecture,

Massachusetts.
Bondanza, J 20111, How to Design and Build a Green Office Building: A Complete Guide to
Making Your New Or Existing Building Environmentally Healthy, 4th edn, Atlantic Publishing
Company, London.
Brumbaugh, JE 2012, Audel HVAC Fundamentals, Volume 1: Heating Systems, Furnaces and
Boilers, 6th edn, John Wiley & Sons, New York.
Coffin, MJ 2012, Direct Digital Control for Building HVAC Systems, 2nd edn, Springer Science
& Business Media, New York.
Gupton, GW 2012, HVAC Controls: Operation & Maintenance, 4th edn, The Fairmont Press,
Inc., New Delhi.
Hartman, TB 2013, Direct digital controls for HVAC systems, 3rd edn, McGraw-Hill, London.
Krarti, M 2016, Energy Audit of Building Systems: An Engineering Approach, Second Edition,
6th edn, CRC Press, Manchester.
Liu, H-C 2013, Information Technology and Computer Application Engineering: Proceedings of
the International Conference on Information Technology and Computer Application Engineering
(ITCAE 2013), 5th edn, CRC Press, Beijing.
Rutkowski, H 2011, Manual J - Residential Load Calculation: 8th Edition, Full, 3rd edn, ACCA,
Salt Lake.
Smith, JG 2009, Construction Management: Subcontractor Scopes of Work, 10th edn, CRC
Press, London.