Effective and efficient solutions for active air conditioning

Principle

Preventive measures (sunshades, screens, etc.) sometimes suffice to keep a hotel cool and comfortable in the summer. An active air conditioning system may be necessary, however, if your hotel systematically requires cooling in summer.
Air conditioning systems have a strong impact on customer comfort, and on your electricity bill, and must be chosen with care.

Explanations

There are two major categories of climate control systems.
• Air conditioners (AC): these systems are designed to provide a relatively constant indoor temperature, regardless of variation in the outside climate or in interior thermal loads. Some systems provide only cooling, while others also heat, reduce humidity and ventilate.
• Reversible heat pumps: heat pumps are used mainly for heating, but reversible models can also cool indoor space. Unlike air conditioning systems, heat pumps reduce the indoor temperature only by a few degrees.

What are the main solutions available?

Type of solution Main solutions available Advantages Drawbacks
Individual cooling systems: room air is cooled when it passes through an evaporator in the room itself. These are called "direct expansion" systems.
• Stand-alone systems: the condenser and evaporator are contained in the same casing.
Drawbacks
• Must be installed in each room to be cooled
• Systems comprising two units; the evaporator is placed in the room t be cooled, the condenser outside the building
• Produces cold air streams (sometimes uncomfortable)
• Tends to dry out ambient air
Advantages
• Easy to install (in general)
• Variable refrigerant volume (VRV) systems in two components provide a good level of comfort (variable cooling capacity) but necessitate a dropped ceiling

Centralised air conditioning with cooling water circuit
Cold water is produced in a water chiller (or may be supplied in part by a natural cold water source, e.g. lake, groundwater, etc.) and distributed by a water circuit.
Advantages
• Provides a good level of comfort (in general)
• Thermal functions and ventilation operate separately (offers flexibility)
Possible distribution systems include:
- low-temperature terminal units (7-12°C): forced air evaporators, air conditioning units,
• Customers can regulate the temperature themselves (with forced air evaporators)
- moderate temperature distributors (15-18°C): dropped ceiling panels, radiant floor panels, etc.
Drawbacks • Can be difficult to install in an existing buildings
NB: a separate circuit supplies fresh air.
• Radiant panels have a limited cooling capacity, and are not suitable for guest rooms.

Centralised air conditioning with cooling air circuit
Air is treated in a central unit and distributed through air ducts.
Advantages Produces moderate-temperature air streams (the air blown in is mixed with outdoor air and air from the rooms)
• Constant air volume systems: the air flow is constant, and the temperature of the air can be regulated,
• Supplies fresh and healthy air (but the air flow can be regulated only in VAV systems
• Variable air volume (VAV) systems: the temperature of the output air is constant, but the flow rate can be regulated.
Drawbacks
- Hard to install in an existing building (bulky air ducts and air treatment unit)
- Fans may consume a lot of electricity
--> these drawbacks are less significant for VAV systems
Heating and cooling units: ground-water, air-air, ground-air, water-air heat pumps.
Heat is drawn from the air (air source heat pumps) or the ground (geothermal heat pumps) and transferred to air or water.
Advantages
• Uses renewable energy
• Free cooling possible with geothermal systems
• Main systems available: water-water, air-water,
systems ("geocooling")
Drawbacks
• Geothermal systems are hard to install in an existing building

General recommendations pertaining to climate control systems
• Centralised systems using a cooling water network are well suited to heating and cooling by zones, and in general provide a good level of comfort. They are also flexible in terms of ventilation and heating/cooling, and are not too difficult to install in an existing building.
• "All air" centralised systems are generally comfortable, because the temperature difference between fan air and room air is limited, and the air flow can be agreeable. Furthermore, they save energy: the air cooler can be equipped with a heat recovery unit, and free cooling obtained when the outdoor air temperature is lower than the indoor air temperature (generally in spring and autumn, and at night in summer). But:
- they can be difficult to install in an existing building,
- ventilators consume a lot of electricity in some installations,
- the amount of fresh air supplied exceed the needs of most hotel rooms (only office space that is occupied full-time requires constant air renewal).

The most highly recommended options are VAV systems: operating costs are roughly 20% lower than for constant air volume systems, thanks to greater energy efficiency.
* If you decided to install a two-component system, we recommend you choose a digital current inverter, to regulate cooling according to room needs, and reduce electricity consumption.
* Stand-alone systems and window air conditioners are not recommended, because they have low energy efficiency and tend to be noisy.

Why should I install a new air conditioning system?
* System choice depends on a number of factors, such as the surface area to be cooled, thermal loads in different zones, etc. Given the technical complexity of this technology, we recommend that you consult a manufacturer or qualified HVAC installer for advice on choosing the equipment that best meets the needs of your hotel.
* Whatever equipment is chosen, we recommend that you be particularly attentive to the energy efficiency ratio of the chiller, which indicates system energy performance. The season energy efficiency ratio can also be a useful indicator. The higher the ratio, the greater the equipment efficiency.
Maintenance and upkeep
* Air conditioning systems must be serviced and maintained to preserve equipment energy efficiency over time.
Do not forget that, before installing an air conditioning system, reducing cooling needs is the top priority, for customer comfort and to keep operating costs at a reasonable level. We recommend the following measures:
* Protect buildings from outside heat by upgrading thermal insulation (underroof/attic and wall installation) and by using exterior sunshades. In hot weather remember to keep doors, windows and shutters closed.
* Consider alternatives to active air conditioning:
- Room and ceiling fans can provide customer comfort in hot weather. They can be used to supplement air conditioning, or as an alternative to air conditioning, particularly in rooms not equipped with air conditioning.
- Ventilation at night or on cool evenings can also be an effective measure to reduce heating needs. Ventilation can be manual (opening windows) or mechanical (see solution no. XX)
* Lastly, it is important to reduce heat from electrical devices and lamps. Remember to turn these devices off when not in use.

Implementation

Organisational aspects
• Group rooms open to guests in cooled zones of the hotel, turn off air conditioning in rooms that are not occupied
Choose programmable thermostats to set cooling temperature limits, to avoid overcooling by customers,
Air rooms for no more than 15-20 minutes when cleaning to retain cooled air,
• Install a cooling system that switches off automatically when windows are open,
Regularly clean and change air conditioner filters
Protect the building from the heat
It is not possible to change the site location, shape or orientation of an existing building, but the interior space can be reorganised: put spaces with low heating needs on the north side of the building, and avoid western exposure for guest rooms. Consider the possibility of roof insulation, as this is the part of the building that receives the most sun in summer. When facades are renovated, exterior walls can be insulated.
Exterior sunshades (the most effective) should be installed:
• Fixed protection on the south side, that let sun through in winter and block it in summer;
• movable protective devices (shutters, shades etc.) on the east and west sides to make the most of winter sun.
Important! Sunshades must not make it hard or impossible to open windows, as this would prevent airing rooms at night or the early morning during hot weather.
Install suitable energy systems and maintain them for good performance over time
Verify that the existing ventilation system ensures sufficient fresh air renewal,
as dictated by regulatory requirements and the needs of the establishment (have a ventilation audit done, if necessary). Equipment must be maintained and serviced regularly.
Ceiling fans with wide airfoil blades increase comfort in summer, by creating a slowly moving air stream.
Important! High ceiling are necessary for ceiling fans.
Extra ventilation at night can cool a building using cool air from outdoors, by opening windows or via a mechanical system. This nocturnal ventilation may be hard to ensure in an existing building, depending on window fittings (opening/closing) and type of mechanical ventilation.
For existing air conditioning systems, the following points should be checked:
• the system is appropriate for needs (conduct a system audit if necessary);
• regular upkeep and maintenance;
°Correct operational parameters (set temperature 26°C or higher; temperature difference with outside temperature limited to 7°C when outside temperature rises above 35°C; timed use).
Use air conditioning in specific areas of the hotel
• guest rooms: occupancy depends on the type of hotel and its setting. Generally rooms are used only for resting and sleeping. As the comfort level
required is lower at night than during the day, ventilation and air conditioning can be regulated accordingly.
• meeting rooms: should be managed according to occupancy.
• restaurant: used at all times, except at night. Calories accumulated can be evacuated by extra ventilation at night.
• indoor swimming pool, sauna, fitness room/gym: air conditioning must control high humidity. The ambient temperature must be higher than in rooms.

Costs

Approximate cost (not including taxes):
• 2 component VRV air conditioning systems: ≈ €150-300/m².
• Forced air systems: ≈ €110-190/m².
• VAV air conditioning systems: ≈ €130-220/m².
• Constant air volume systems: ≈ €120-190/m²
Approximate payback time:
• Possibly < 2-5 years.
It should be noted that costs and payback times are highly dependent on the local setting and the initial situation of the hotel.

Examples

The 35-room Hotel Olympia in Beausoleil installed a solar thermal system combined with a gas-fired heat pump to meet heating, sanitary hot water and air conditioning needs. The cost of installing 8 m² of solar panels and replacing the existing heat pump with a new model (63 kW heating capacity) came to €45,500 (excluding taxes, including labour costs). Although the energy savings are hard to evaluate, the advantages of this new installation are lower management costs for the establishment and less noise for the neighbours, compared to the previous heat pump.
The Hotel de la Pérouse in Nantes installed automatic heating/cooling controls: this system, installed when the building was construction allows the heating or air conditioning to be switched off when a window is open.
The owner of the 43-room Hotel Nota Bene in Montceau-les-Mines decided to renovate and bring the hotel's DRV heating/cooling system up to current regulatory standards.
The existing system had operating and excess consumption problems. To avoid taking rooms out of service, work was done to replace room units (indoor and outdoor), and units in the dining room and reception area, while conserving the existing cooling piping. The work was completed in five weeks, and has achieved a 49% improvement in the coefficient of performance (COP) for the air condition installation.

Benefits

Cost reduction
Upgrading to an energy-efficient air conditioning system can reduce annual energy consumption for space cooling by 50%.
Solutions Implementation Investment Benefits
Organisational aspects ++ ++ -
Building envelope insulation -- -- ++
Window sun protection + + + +
Use of appropriate system + -- +
Source: US Department of Energy.

Reduced CO2 emissions
• For a hotel of 1,000 m² that uses 37.5 kWh/m² of electricity for air conditioning annually, and applying emission factors for France, a 50% savings in energy consumption represents:
1.58 t CO2 eq of avoided emissions each year
Emission factors for electricity in France: 84.3 g CO2 / kWh.
Emission factors for natural gas in France: 331 g CO2 / kWh (Source: ADEME).