Section 9: Comfort cooling

  1. Section 9

    Section 9

    9.1 Introduction

    This section gives guidance on specifying comfort cooling for new and existing buildings to meet relevant energy efficiency requirements in the Building Regulations. It includes guidance on using SBEM to calculate the carbon dioxide emissions associated with comfort cooling in new buildings.

    9.2 Scope of guidance

    The guidance covers the specification of refrigeration plant efficiency in terms of the seasonal energy efficiency ratio (SEER), which is the value used by SBEM to calculate the carbon dioxide emission rate for a new building. SBEM allocates standard correction factors37 to the performance of cooling plant to account for the use of the different systems for distributing cooling to the spaces. Evaporative cooling and desiccant cooling systems are not within the scope of this guidance.

    9.3 Key terms

    Cooling plant means that part of a cooling system that produces the supply of cooling medium. It does not include means of distributing the cooling medium or the delivery of the cooling into the relevant zone. It may consist, for example, of a single chiller or a series of chillers.

    Cooling system means the complete system that is installed to provide the comfort cooling to the space. It includes the cooling plant and the system by which the cooling medium effects cooling in the relevant zone and the associated controls. This will in some cases be a complete packaged air conditioner.

    Energy efficiency ratio (EER) for chillers is the cooling energy delivered into the cooling system divided by the energy input to the chiller, as determined by BS EN 1451138.

    In the case of packaged air conditioners, the EER is the energy removed from air within the conditioned space divided by the effective energy input to the unit, as determined by BS EN 14511 or other appropriate standard procedure. The test conditions for determining EER are those specified in BS EN 14511.

    Part load energy efficiency ratio is the cooling energy delivered into the cooling system divided by the energy input to the cooling plant. Part load performance for individual chillers is determined assuming chilled water provision at 7°C out and 12°C in (at 100% load), under the following conditions:

    ****Table****

    Seasonal energy efficiency ratio (SEER) is the total amount of cooling energy provided divided by the total energy input to a single cooling unit, summed over the year.

    European Seasonal Energy Efficiency Ratio (ESEER) is the SEER of a cooling unit as determined under the Eurovent Certification scheme.

    Plant seasonal energy efficiency ratio (PSEER) is the total amount of cooling energy provided divided by the total energy input to the cooling plant (which may comprise more than one cooling unit), summed over the year.

    9.4 Comfort cooling in new and existing buildings

    For comfort cooling systems in new and existing buildings:

    a. cooling units should comply with European Commission Regulation No 327/2011 for fans driven by motors with an electrical input power between 125 W and 500 kW, and Regulation No 206/2012 for systems with a cooling capacity of up to 12 kW, both implementing Directive 2009/125/EC with regards to ecodesign requirements for energy-related products

    b. the full load energy efficiency ratio (EER) of each cooling unit of the cooling plant should be no worse than recommended in Table 33

    c. controls should comply with BS EN 15232:201239 Band C and be no worse than recommended in Table 34.

    ****Table 33   Recommended minimum energy efficiency ratio (EER) for comfort   cooling****

    ****Table 34****

    9.5 Calculating the seasonal energy efficiency ratio for SBEM

    The value of the SEER to be used in the SBEM tool can be calculated in a number of ways according to the availability of information and the application.
    In general, where an industry approved test procedure for obtaining performance measurements of cooling units at partial load conditions exists, and the cooling load profile of the proposed building is known, the SEER of the cooling unit is given by:

    ****Equation 10****

    where:

    EERx is the EER measured at the load conditions of 100%, 75%, 50% and 25% at the operating conditions detailed under the part load energy efficiency ratio in Section 9.3

    and:

    a, b, c and d are the load profile weighting factors relevant to the proposed application. The following sections describe how the SEER may be calculated for the specific cases of:

    • cooling units with no part load performance data
    • unknown load profiles
    • office-type accommodation
    • other buildings with known load profile data
    • multiple-chiller systems
    • systems with free cooling or heat recovery
    • absorption chillers and district cooling.

    Cooling units with no part load performance data
    For cooling units that have no part load data, the SEER is the full load EER.

    Unknown load profiles

    For applications where the load profile under which the cooling plant operates is not known but there is some data on chiller part load EER, then:

    a. for chillers where the full and half load (50%) EERs are known, the SEER is the average of the EERs, i.e. the 100% and 50% are equally weighted

    b. for chillers with four points of part load EER, the SEER is calculated using Equation 10 with each EER weighted equally, i.e. a, b, c and d each equal to 0.25

    c. if the chiller used does not have data for four steps of load, then the weights are apportioned appropriately.

    Office-type accommodation

    For applications in general office-type accommodation, the following weighting factors can be taken as representative of the load profile:

    ****Table****

    These weighting factors are the same as those used for the determination of the European Seasonal Energy Efficiency Ratio (ESEER). Most manufacturers publish ESEER figures and these can be verified by reference to the Eurovent Certification website at www.eurovent-certification.com. The ESEER value is then used as the SEER in the SBEM calculation.

    Examples

    1. For a single chiller with EER of 2.9 (known at full load only): SEER2.9

    2. For a chiller with 100% and 50% EERs of 2.0 and 2.5 respectively in a building with unknown load profile: SEER2.25

    3. For a chiller with unknown application load profile and part load EERs of EER100%2.89, EER75%3.93, EER50%4.89 and EER25%4.79:
    SEER0.252.890.253.930.254.890.254.794.125

    4. If the same chiller is used in an office then the ESEER weighting factors are used: SEERESEER0.032.890.333.930.414.890.234.794.49

    Other buildings with known load profile

    If the load profile is known from detailed simulation or prediction, the SEER may be derived from Equation 10 above using appropriate weights and EERs at given loads.

    Multiple-chiller systems

    For plants with multiple-chillers, a plant seasonal energy efficiency ratio (PSEER) value may be calculated based on the sum of the energy consumptions of all the operating chillers. In this case care must be taken to include all the factors that can influence the combined performance of the multiple-chiller installation.

    These will include the:

    • degree of oversizing of the total installed capacity
    • sizes of individual chillers
    • EERs of individual chillers at actual operating conditions
    • control mode used: e.g. parallel, sequential, dedicated low load unit
    • load profile of the proposed building
    • building location (as this determines ambient conditions).

    When these are known it may be possible to calculate a PSEER which matches the proposed installation more closely than by applying the simplifications described earlier. This PSEER value is then used as the SEER in the SBEM calculation.

    Systems with free cooling or heat recovery

    Systems that have the ability to use free cooling or heat recovery can achieve a greater SEER than more conventional systems. In these cases the SEER must be derived for the specific application under consideration.

    Absorption chillers and district cooling

    Absorption chillers may be used in conjunction with on-site CHP or a community or district heating system. The carbon dioxide emissions are calculated in the same way as when using CHP for heating. The control system should ensure as far as possible that heat from boilers is not used to supply the absorption chiller.

    The minimum full load EER of the absorption chillers should be no worse than 0.7.

    Where a district cooling scheme exists, lower carbon dioxide emissions may result if the cooling is produced centrally from CHP/absorption chillers, heat pumps or high efficiency vapour compression chillers. The district cooling company will provide information on the carbon dioxide content of the cooling energy supplied, and this figure can then be used to calculate the carbon dioxide emission rate for the building.

    9.6 Supplementary information

    ****Table****