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Heat Pumps for Larger Buildings

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Heat pumps are increasingly being used in medium and large buildings to provide both heating and cooling. If specified and installed correctly they present a very good opportunity to save energy and …

Heat pumps are increasingly being used in medium and large buildings to provide both heating and cooling. If specified and installed correctly they present a very good opportunity to save energy and reduce carbon emissions compared to traditional building heating and cooling technologies. This application note provides an overview of the types of heat pumps available along with the advantages and constraints of installing them in larger buildings.

The key appeal of heat pumps is that they have the ability to take low grade heat from a source and transfer it at a higher temperature to where it is needed in a relatively energy efficient manner. There is a great deal of flexibility in the heat sources available, for example external air, underground pipework, boreholes and local watercourses and ponds are all commonly used sources. Choosing the most appropriate heat source for a building will depend on weighing up all the advantages and constraints of the options available and looking at the whole life costs of the installation. The relatively high installation costs compared to gas boilers, especially with ground source heat pumps, needs to be considered against the lower running costs and carbon reduction that can be achieved.

A heat pump will in most cases save on carbon emissions compared to a fossil fuel boiler, but the exact carbon savings that can be achieved will depend on a number of factors. The heat source should be closely matched with the building’s heat requirements, and the most energy efficient components should be used in both the heat pump and the distribution system. The control systems should be set up to ensure that heating and cooling is only provided where and when required. The building fabric should be designed to ensure heat loss is minimised. It is only by taking a holistic view of the entire heating and cooling systems for a building that a proper assessment of the suitability for heat pumps can be made.

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  • 1. APPLICATION NOTEHEAT PUMPS FOR LARGER BUILDINGSKeeran JugdoyalApril 2013ECI Publication No Cu0179Available from www.leonardo-energy.org
  • 2. Publication No Cu0179Issue Date: April 2013Page iDocument Issue Control SheetDocument Title: Heat Pumps for Larger BuildingsPublication No: Cu0179Issue: 01Release: April 2013Author(s): Keeran JugdoyalReviewer(s): Bruno De WachterDocument HistoryIssue Date Purpose1 April 2013 First publication, in the framework of the Good Practice Guide234DisclaimerWhile this publication has been prepared with care, European Copper Institute and other contributors provideno warranty with regards to the content and shall not be liable for any direct, incidental or consequentialdamages that may result from the use of the information or the data contained.Copyright© European Copper Institute.Reproduction is authorised providing the material is unabridged and the source is acknowledged.
  • 3. Publication No Cu0179Issue Date: April 2013Page iiCONTENTSSummary ........................................................................................................................................................ 1Introduction.................................................................................................................................................... 2Principles of Heat Pump Operation................................................................................................................. 3Types of Heat Pumps ...................................................................................................................................... 5Economic and environmental evaluation........................................................................................................ 7Carbon Emissions Comparisons..............................................................................................................................7Relative Life Cycle Costs .........................................................................................................................................8Heat Pump Applications ............................................................................................................................... 14Heating ................................................................................................................................................................14Cooling ................................................................................................................................................................14Heat Recovery.......................................................................................................................................................15Dehumidification ..................................................................................................................................................15Domestic Hot Water.............................................................................................................................................15Advantages and constraints of using heat pumps in larger buildings ............................................................ 16Advantages ...........................................................................................................................................................16Heating and Cooling in a Single Unit ......................................................................................................16Reduced Maintenance Compared to Gas Boilers...................................................................................16Higher Efficiency than Electric Radiant Heaters.....................................................................................16Recovery of Waste Heat.........................................................................................................................17Constraints............................................................................................................................................................17Low Output Temperature.......................................................................................................................17Reduced Efficiencies when Large Temperature Difference Between Source and Output.....................17Difficult to Retrofit to Older Buildings....................................................................................................17Improving Heat Pump Efficiency................................................................................................................... 19Use High Efficiency Compressors .........................................................................................................................19Refrigerant Choice................................................................................................................................................19Heat Exchanger Size and Materials ......................................................................................................................19Match Heat Sources and Sinks .............................................................................................................................20Improve Building Fabric........................................................................................................................................20Use Intelligent Controls ........................................................................................................................................20Conclusion .................................................................................................................................................... 21
  • 4. Publication No Cu0179Issue Date: April 2013Page 1SUMMARYHeat pumps are increasingly being used in medium and large buildings to provide both heating and cooling. Ifspecified and installed correctly they present a very good opportunity to save energy and reduce carbonemissions compared to traditional building heating and cooling technologies. This application note provides anoverview of the types of heat pumps available along with the advantages and constraints of installing them inlarger buildings.The key appeal of heat pumps is that they have the ability to take low grade heat from a source and transfer itat a higher temperature to where it is needed in a relatively energy efficient manner. There is a great deal offlexibility in the heat sources available, for example external air, underground pipework, boreholes and localwatercourses and ponds are all commonly used sources. Heat pumps that use external air as the heat source are relatively cheap and easy to install, howeverthey have higher running costs and are more susceptible to a reduction in their operational efficiencyduring colder weather compared to other types of heat pumps. With these systems, extra attentionshould go to perfecting the design, installation and control of the system for maximal efficiency. Heat pumps which use underground pipework or water courses as their heat source have higherinstallation costs and may require large areas of land, however they do have more stable operatingefficiencies across the entire heating season. With these systems, extra attention should go tomitigation of the installation cost, for instance by combining the installation with other ground works.Choosing the most appropriate heat source for a building will depend on weighing up all the advantages andconstraints of the options available and looking at the whole life costs of the installation. The relatively highinstallation costs compared to gas boilers, especially with ground source heat pumps, needs to be consideredagainst the lower running costs and carbon reduction that can be achieved.There is also a great deal of flexibility in the ways in which heat pumps can be used to heat and cool buildings,as they can be integrated with many traditional building distribution systems. They are suitable for use with airbased systems such as air handling units as well as water based systems such as fan coil units, under floorheating and chilled beams. Heat pumps provide lower output temperatures than traditional gas boilers andradiant electric heaters. For this reason the heat emitters they are used with need to be physically larger thantraditional heat emitters. This may require extra space to be provided in the buildings for larger radiators, fancoil units, air handling units and air ducts. Space savings can be made in the plant rooms, because there is noneed to provide separate heating and cooling plants. The lower output temperatures of heat pumps mean thatthe building fabric must be designed and built to a high standard to ensure that insulation levels and airtightness are as good as is practicable.Heat pumps can also be used for dehumidification in larger buildings. Dehumidification can be undertaken fora number of reasons including improving thermal comfort, protecting the building fabric and stored goods, andfor drying processes.A heat pump will in most cases save on carbon emissions compared to a fossil fuel boiler, but the exact carbonsavings that can be achieved will depend on a number of factors. The heat source should be closely matchedwith the building’s heat requirements, and the most energy efficient components should be used in both theheat pump and the distribution system. The control systems should be set up to ensure that heating andcooling is only provided where and when required. The building fabric should be designed to ensure heat lossis minimised. It is only by taking a holistic view of the entire heating and cooling systems for a building that aproper assessment of the suitability for heat pumps can be made.
  • 5. Publication No Cu0179Issue Date: April 2013Page 2INTRODUCTIONHeat pumps are increasingly being used to provide both heating and cooling for buildings of all sizes and uses.They are chosen for their ability to be installed in a wide range of configurations, as well as their potential tosave energy and carbon compared to some traditional building heating and cooling systems. This ApplicationNote provides a general introduction to heat pumps and their use in medium to large sized buildings.Heat pumps are a well-established technology and have been used for many years as a cost effective methodof transferring heat from one place to another. They are simple to operate, with only a few moving parts. Thismakes them robust and reliable. The key appeal of heat pumps is that they are able to extract heat from a lowtemperature source, and discharge heat at a higher temperature whilst only using a relatively small amount ofenergy in the process. This means that the “heat source” will actually be colder than the building itself. Theheat pump concentrates the heat extracted from the heat source through compression, which makes itpossible to output it at a higher temperature. Also, unlike boilers, electric heat pumps do not require a freshair supply or a flue, and so the plant room can be located in any part of a building as long as there is a suitableconnection to a heat source.Heat pumps are very versatile machines, for example they can be found in the home used in refrigerators, inoffices used in air conditioning systems and in factories used in heat recovery systems. For medium and largersized buildings they have traditionally only been used for cooling purposes, but this has been changing inrecent times as they have been found to be very capable of also providing cost effective heating. A single heatpump can be used for both heating and cooling duties. As such they can be used in conjunction with airhandling units, radiators, fan coil units, under floor heating and chilled beams. They can also be used toimprove the operational efficiency of existing heating and cooling systems when used as part of a heatrecovery system. They can reclaim heat which would otherwise have been wasted from heat sources such asventilation extract ducts, boiler rooms and server rooms, and supply it to where it is needed.
  • 6. Publication No Cu0179Issue Date: April 2013Page 3PRINCIPLES OF HEAT PUMP OPERATIONHeat pumps operate on the principle that a liquid will extract heat from its surroundings when it evaporates,and will discharge heat when condensing from a gas back to a liquid. All electric heat pumps are made up offour main components: A heat exchanger known as a condenser. A compressor, driven by an electric motor. A heat exchanger known as an evaporator. An expansion valve.These components are connected via a pipework circuit through which a refrigerant fluid is circulated, asshown in Figure 1.The steps involved in the operation of a heat pump are as follows: Liquid refrigerant passes into the Evaporator (1) and the combined operation of the Compressor (2)and the Expansion valve (4) causes the pressure in the Evaporator to drop. This decrease in pressure causes the refrigerant to evaporate. This evaporation process causes heat tobe extracted from the Heat Source (5) as the refrigerant changes from liquid to gas. The heated refrigerant gas is then forced through the Compressor into the Condenser (3). The forceof the gas pushing on the Expansion Valve causes a back pressure to form in the Condenser. This increase in pressure causes the refrigerant to condense back into a liquid, discharging heat to theHeat Sink (6). The cooled liquid refrigerant flows through the Expansion Valve back into the Evaporator.(5) Heat source:Heat in(6) Heat sink:Heat out(3)Condenser(1)Evaporator(2) Compressor(4) ExpansionvalveFlow of refrigerantaround the heatpump circuitElectricity is typicallyused to drive thecompressorFigure 1 – Schematic diagram of the main components of a heat pump
  • 7. Publication No Cu0179Issue Date: April 2013Page 4A heat pump can be used for both heating and cooling. When heating is required, then the heat emitted fromthe condenser is used. When cooling is required, the cooling effect from the evaporator is used. In order tofacilitate this there needs to be diverting ‘change-over’ valves or dampers installed in the plant room.The output temperature of a heat pump is dependent on both the heat source temperature and the energyput into the system by the compressor. The greater the energy put into the system by the compressor, thegreater the increase in temperature between the heat source and the heat sink. This means that the electricityconsumed by a heat pump increases when either the temperature of the heat source drops, or thetemperature required by the heat sink increases. This fact is important to bear in mind when using external airas a heat source. On very cold days, the electricity consumption of a heat pump can often be significantlyhigher than on milder days.The measure of the performance of a heat pump is known as the coefficient of performance (COP) and isdefined as follows:𝐶𝑂𝑃 =𝐸𝑛𝑒𝑟𝑔𝑦 𝑜𝑢𝑡𝑝𝑢𝑡𝐸𝑙𝑒𝑐𝑡𝑖𝑐𝑖𝑡𝑦 𝑖𝑛𝑝𝑢𝑡For example, if a given heat pump has a COP of 5 when the heat source is at 10°C and the output temperatureis at 45°C, this means that for every unit of electrical energy input, 4 units of heat are output. Or in otherwords, the heat pump will use 4 times less electricity than an equivalent electric radiant heater to do the samework. Consequently, this also means that there is also 5 times less carbon emitted.The COP of a heat pump will fall as the difference between the heat source and heat sink increases. Forexample, if the same heat pump is now working with a heat source at 0°C, the COP is likely to be closer to 2.75.Figure 2 show a typical relationship between COP and the temperature difference between the source andsink. Therefore it is important when assessing the performance of heat pump to understand how its COP varieswith changes in input and output temperatures. The average performance of a heat pump over the entireheating season is often referred to a the Seasonal Performance Factor (SPF)Figure 2 – Example of how the COP changes with source temperature for a typical commercial electric heatpump0246810120 10 20 30 40 50 60CoefficientofPerformance(COP)Difference between source and sink temperature (°C)
  • 8. Publication No Cu0179Issue Date: April 2013Page 5TYPES OF HEAT PUMPSHeat pumps are typically split into two main types; air source heat pumps (ASHP) and ground source heatpumps (GSHP). As the name suggests ASHPs use air, typically from outside or from a plantroom, as the heatsource. GSHPs can use a wide variety of heat sources, for example: Water filled pipework buried in the ground; Water filled pipework embedded in the piling foundations of the building itself; Water filled pipework inserted into a body of water such as a pond or river; or Water abstracted from a boreholeThe subset of GSHPs which use borehole water or bodies of water are sometimes referred to as water sourceheat pumps (WSHPs). For the purpose of this Application Note, WSHPs will be treated as being effectively thesame as GSHP as there is little difference in their performance when used in larger buildings. The key benefitof an ASHP over a GSHP is that they are easier to install. This is because they do not require any additionalpipework, excavations, land or watercourses to be used as a heat source.The key benefit of a GSHP over an ASHP is that there is very little variation in the heat source temperatureduring year. This is because the temperature approximately 1 m below the surface typically only varies byapproximately 2 – 3 °C during a year. For example, in UK the ground temperature typically varies between 10 –12°C across the year. Having a constant heat source temperature means that even on very cold days the heatpump compressor does not have to work any harder to produce the same output temperature. Or to put itanother way, GSHPs tend to have a higher SPF than ASHPs. Therefore GSHPs will almost always have lowerrunning costs than an equivalent ASHP, despite having a higher initial capital cost.The SPF of ASHPs is likely to be lower in Northern and Eastern Europe compared to Western and SouthernEurope, as the extremes in winter temperatures are greater in these areas. Results from recent studies showthat SPF for ASHPs in the UK average around 2.21, whereas in Germany it is 2.9 and in Switzerland between 2.5- 2.82Both ASHPs and GSHPs can be used with water or air as the heat sink. Therefore, ASHPs are commonlyreferred to as either ‘air to air’ or ‘air to water’ heat pumps, and GSHPs are commonly referred to ‘water to air’or ‘water to water’ heat pumps depending on the configuration used.With ASHPs the main unit is usually installed inside, with the evaporator unit installed outside the building,either mounted on an external wall, on the roof or on the ground close by. The evaporator is usually enclosedin a protective housing and an integral fan is used to blow air over them. In GSHP systems, the heat pump unitis typically installed within the building and the evaporator is connected to a water filled pipework systemwhich runs to the external heat source. For buried pipework systems, the size of the ground collector willdepend on the heat demand from the building. Car parks and school playing fields are often an ideal locationto install large buried pipework systems. Where space is tight, then smaller Direct Expansion (DX) copperpipework collectors can be installed in the ground. In DX systems, the buried pipework is the heat pump1http://www.decc.gov.uk%2Fassets%2Fdecc%2F11%2Fmeeting-energy-demand%2Fmicrogeneration%2F5045-heat-pump-field-trials.pdf “Getting Warmer: A Field Trial of Heat Pumps” 2010, Energy Saving Trust2http://wp-effizienz.ise.fraunhofer.de “Wärmepumpen-Effizienz” 2011, Fraunhofer ISE
  • 9. Publication No Cu0179Issue Date: April 2013Page 6evaporator itself and a refrigerant is circulated in the pipework under the ground. Vertical boreholes with thepipework installed within it is also an option where space is limited.Heat pumps are available as ‘single stage’ and ‘two stage’ units. Two stage units are effectively two heat pumpcircuits combined into a single unit. They are typically used with ASHPs, with a single stage being used duringmild weather and the second stage being switched on during periods of extreme cold or heat. Two stage heatpumps can also be used when retro-fitting a heat pump to an older heating system to produce higher outputtemperatures. The maximum output temperature of a single stage heat pump is typically around 45°C – 55°C.This is perfectly adequate for many types of heating systems, however many older radiators require inputtemperatures of up to 90°C. Two stage heat pumps have the potential to produce these higher outputtemperatures. This is because the first stage boosts the temperature up to around 45°C – 55°C and the secondstage can then raise the temperature up to the required higher output temperature. These higher sourcetemperatures are also more suitable for the generation of domestic hot water.Many larger buildings are split into separate zones, each of which can be controlled to its own temperature setpoint. In certain situations one zone will require heating while another requires cooling. This is especiallycommon in buildings with large glass facades where the solar gains from the sun can heat up part of a buildingvery quickly. In order to meet this simultaneous demand for heating and cooling, there are heat pumpsavailable with two or more refrigeration circuits. One circuit can provide the heating, whilst the other providesthe cooling. An advantage of this arrangement is that the heat rejected from the cooling circuit can be used asthe heat source for the heating circuit. This improves the COP of the heat pump as a whole.
  • 10. Publication No Cu0179Issue Date: April 2013Page 7ECONOMIC AND ENVIRONMENTAL EVALUATIONCARBON EMISSIONS COMPARISONSThe following table shows a comparison of the carbon emissions of traditional heating methods versus anumber of heat pump types. The figures for the carbon emissions of heat pumps presented here are on theconservative site and can be significantly lower, for two reasons:1) For the purpose of the comparison, an average efficiency/SPF has been used, based on a typical plantavailable on the market, rather than the ‘best in class’ performance. This means that underfavourable circumstances, the carbon emissions of a well-chosen and well-installed heat pump will falleven further below the emissions of a natural gas heating system2) The carbon emission factors used in the table are the average for the EU as a whole today. The carbonemissions for electricity are expected to continue their steady decrease across Europe in the comingyears, as more low carbon electricity sources will come into use, implementing the EU target of 20%renewable electricity by 2020. This will cause the average emissions associated with heat pumps overtheir life-cycle to be lower than the figures presented here.Table 1- Comparison of typical carbon emissions for direct electrical heating, gas boilers and heat pumpsDirect electricheatingNatural gas heating GSHP ASHPAnnual heat load 200,000 kWh 200,000 kWh 200,000 kWh 200,000 kWhTypical averageefficiency / SPF100% 90% 3.4 2.6Annual energyconsumption200,000 kWh 222,222 kWh 58,824 kWh 76,923 kWhEuropean averageCO2 emissionsfactor30.46 kgCO2/kWh 0.202 kgCO2/kWh 0.46 kgCO2/kWh 0.46 kgCO2/kWhAnnual carbonemissions92,000 kgCO2 44,889 kgCO2 27,059 kgCO2 35,385 kgCO2The figures presented in this table will also depend significantly on the country in which the heat pump isinstalled. For example, in the UK, where electricity carbon emissions are relatively high, the natural gas carbonemissions are relatively low, and the winters are relatively cold, the relative advantage in carbon emissions forheat pumps becomes smaller. Conversely in countries with very low electricity carbon emission factors andrelatively mild winters, such as France, which has a significant amount of nuclear power, heat pumps offerhigher carbon emission reductions. It is also important to bear in mind countries which have low electricitycarbon emissions at night, such as Sweden which uses hydro power to meet its electricity baseload, can haverelatively low carbon emission for direct electric heating with night time accumulators.Note that oil and other fossil fuels used in boilers have higher carbon emissions than natural gas boilers, and soheat pumps have the potential to provide carbon emission savings over any fossil fuel based boilers.3http://www.covenantofmayors.eu/IMG/pdf/technical_annex_en.pdf “Technical annex to the SEAP templateinstructions document: The Emissions Factor” Covenant of Mayors
  • 11. Publication No Cu0179Issue Date: April 2013Page 8RELATIVE LIFE CYCLE COSTSA key barrier to the installation of heat pumps, especially GSHPs is the initial capital costs. For exampletraditional gas boilers typically cost between €80 - €150 / kW for a full installation. The typical installed cost foran ASHP is approximately €250 - €300 /kW, and approximately €1,000 - €1,500 / kW for GSHPs4. If groundworks are integrated into other ground works that have to be executed for the construction of the building, itshould be possible to reduce the installation cost to approximately €800 / kW. Financial incentives fromgovernments are available in many countries to assist with the initial costs of installing a heat pump.The following table shows the estimated life cycle costs of various heating systems for a building, assuming anannual energy demand of 200,000 kWh, a peak heat demand of 150 kW, and a plant life of 30 years.Note that the SPF for both GSHP and ASHP will improve in time as the technology improves and as newinstallations are provided in accordance to best practices. Therefore, it is likely that as time goes on the wholelife cost of ownership for new heat pumps will continue to decrease.Table 2 – Example of a Life Cycle Cost comparison for gas boilers and heat pumpsGas boiler GSHP ASHPAnnual heat load(kWh)200,000 200,000 200,000Plant poweroutput (kW)150 150 150Assumed fuelcost (€/kWh)5 0.055 0.16 0.16Installation costs(€)Low scenario12,000High scenario22,500Low scenario120,000High scenario225,000Low scenario37,500High scenario45,000Seasonalefficiency / SPF(low/high scenarios)80% 90% 80% 90% 3.0 4.0 3.0 4.0 2.0 3.0 2.0 3.0Annual energyconsumption(MWh)250 222 250 222 67 50 67 50 100 67 100 67Annual runningcosts (€,000)13.8 12.2 13.8 12.2 10.7 8.0 10.7 8.0 16.0 10.7 16.0 10.7Total cost after30 years (€,000)6 422 377 433 387 438 359 543 464 515 356 522 363Total cost after30 years, withincentives422 377 433 387 249 209 328 288 267 187 272 1934“SPON’S M&E 2010 Price book” Spon Press, 40thEdition. 2010 ISBN 13: 978-0-203-87242-05http://www.energy.eu/ May 2012 average retail natural gas and electricity costs for Europe6Discount rate of 4% assumed. Electricity inflation rate of 3.96%, source EuroStat data code nrg_pc_204
  • 12. Publication No Cu0179Issue Date: April 2013Page 9The last line of this table shows the life cycle cost in case of a 25% reduction on the purchase and installationcost of the heat pump (through a direct grant or tax reduction) combined with a 50% reduction on the price ofelectricity used for the heat pump. This represents an approximation of the more favourable regimes ofgovernment incentives to promote heat pumps that exist in the EU.There are a number of different types of incentives in individual member states, taking the form of: Heat pump tariffs for electricity – These are common in countries such as Germany and Austria. Theyoffer reductions of around 40 – 60% on electricity prices when used with a heat pump. Some areoffered with 100% green electricity. Direct grants – Grants are available in a number of member states including Finland and Germany. InFinland up to 25% of the heat pump and its installation costs are available when a heat pump isinstalled in an existing building. Tax based incentives – These can take many forms including deductions from taxable income,reduction of tax burden and VAT re-imbursements. In France, for example, 40% of the cost for eligibleunits can be deducted from the income tax burden Preferred interest – These loans can be offered by governments or private banks. They often comewith conditions surrounding the technology to be used and the savings to be achieved. “Feed in” tariffs – In certain member states a tariff is available which is payable for the heat generatedby a qualifying heat pump. In the UK a tariff of £0.047/kWh is available on GSHPs less than 100kWthand £0.034/kWh on GSHPs above 100kWthThese incentives are intended to fill the gap in life cycle cost between heat pumps and traditional gas boilers,in order to yield the carbon emission reductions that heat pumps bring about. As heat pump technologyimproves and capital costs reduce, the need for these incentives reduces.Are these incentives a wise investment from the government? Or in other words, is the cost per carbonemission reduction reasonable?
  • 13. Publication No Cu0179Issue Date: April 2013Page 10Table 3 shows the gap in life cycle cost between a GSHP and a gas boiler per ton of CO2 saved, with differentSPFs and installation costs.
  • 14. Publication No Cu0179Issue Date: April 2013Page 11Table 3 – Cost per tonne of carbon emissions saved compared to a gas boiler for a range of GSHP costs andSPFs7Euro / ton CO2emissions savedGSHP Low installationcost (€800 / kW)GSHP Averageinstallation cost (€1,000/ kW)GSHP High installationcost (1,200 kW)SPF = 3.1 113 178 2443.2 86 148 2103.3 64 123 1823.4 45 101 1573.5 29 83 1363.6 15 67 1183.7 2 52 1023.8 - 40 883.9 - 28 754 - 18 64The LCC of the installation is lower than that of a gas boiler, so no financial incentives are neededBelow €50/ton CO2Between €50 and €100 / ton CO2Above €100 / ton CO27A 150kW gas boiler, 90% efficiency, 200,00 kWh output per year, €12,000 capital costs, 30 year life.Furthermore, the discount rate of 4% and an inflation rate of 3.96% are assumed.
  • 15. Publication No Cu0179Issue Date: April 2013Page 12Table 3 shows that as GSHP costs fall to the region of €800/kW and the SPF improves to 3.7, then they have alower life cycle cost than an equivalent gas boiler, and so incentives of any form are not required. The highinstallation costs are still a big hurdle to overcome. Attention should go to mitigating those costs. For instance,the viability of GSHP installations increases significantly if the ground work costs can be incorporated intothose of other ground work being undertaken for the building.
  • 16. Publication No Cu0179Issue Date: April 2013Page 13Table 4 – Cost per ton of carbon emissions saved compared to a gas boiler for a range of ASHP costs and SPFs8Euro / ton CO2emissions savedASHP Low installationcost (€200 / kW)ASHP Averageinstallation cost (€250 /kW)ASHP High installationcost (€300 kW)SPF = 2.50 145 176 2072.55 105 133 1622.6 72 98 1252.65 45 69 942.7 21 45 682.75 2 23 452.8 - 5 262.85 - - 92.9 - - -2.95 - - -The LCC of the installation is lower than that of a gas boiler, so no financial incentives are neededBelow €50/ton CO2Between €50 and €100 / ton CO2Above €100 / ton CO2Table 5 shows that for ASHPs, the life cycle cost is much less affected by the installation cost. Consequently,the impact of the SPF on the life cycle cost is much higher. Only a small change in the SPF of ASHPs can have asignificant impact on the savings that can be achieved. This highlights why it is very important to ensure thatASHPs are correctly specified, installed and operated.8A150kW gas boiler, 90% efficiency, 200,000 kWh output per year, €12,000 capital costs, 30 year life.Furthermore, the discount rate of 4% and an inflation rate of 3.96% are assumed.
  • 17. Publication No Cu0179Issue Date: April 2013Page 14HEAT PUMP APPLICATIONSThere are three main applications for heat pumps in larger buildings, namely: Heating Cooling Heat recovery DehumidificationIn addition to these main applications, heat pumps can be used to produce domestic hot water, although forreasons discussed further in this section, they may not offer the most energy and cost efficient solution for thisapplication.HEATINGWhen heat pumps are used for building heating, the wider heat distribution systems and building fabric needto be carefully designed to ensure they are making maximum use of the relatively low temperatures produced.For example, the radiators, air handling units and fan coil units used with water temperatures of 55°C – 45°Cneed to physically larger than the equivalent high temperature units. This means that extra wall and ceilingspace is required and the architects need to take this into consideration when providing space for heatemitters. Also radiators have traditionally been installed underneath windows to counteract any downdraughts of cold air coming into the room. Lower temperature radiators are much less effective at achievingthis as they do not produce as strong circulating air currents within a room. In order to allow for this thebuilding fabric need to be as air tight and insulated as is practicable, especially around windows. For largerspaces fan coil units and air handling units are always recommended over radiators.The most effective method of maximising the benefit of heat pumps in water based (hydronic) heating systemis through the use of under floor heating systems. This is because the under floor heating systems have verylarge heating surface areas, allowing them to be used with water temperatures as low as 35°C. This results in arelatively high SPF and low running costs. There can be an issue with using under floor heating systems insome larger buildings such as offices as there are often electrical and communications services recessed in thefloor, which may restrict the ability to install the under floor pipework. Another issue with under floor heatingis that they tend to have long warm up times compared to other forms of heating. This should be taken intoaccount when used with a building with high air change rates, for example buildings where windows are openand shut for cooling purposes and older buildings.COOLINGASHPs have been used in air conditioning systems for many years, and their use with large buildings is wellestablished. GSHPs are a less well established technology when used for cooling operations, however they stillpresent the potential to save operational costs against ASHP.Heat pumps can be used to provide cooling to buildings via the conventional air conditioning distributionsystems such as air handling units, fan coil units, DX units and chilled beams. With the exception of DX units,the same distribution systems can also be used to provide the heating in the winter. If radiators or under floorheating systems are employed in the building, then separate cooling systems will also need to be provided.If the pipework is installed in the appropriate way, heat pumps can be used for ‘free cooling’ during relativelymild days. This is where the cool ground source or external air is used to cool the chilled water directly,without the need to operate the refrigeration cycle. It is not completely ‘free’, as any circulating pumps andcooling fans will still need to operate.
  • 18. Publication No Cu0179Issue Date: April 2013Page 15HEAT RECOVERYHeat pumps can very effectively be used in large buildings as a means of recovering heat which wouldotherwise be wasted. They are commonly employed in ventilation extract ducts where warm air is expelled tothe atmosphere. In this situation, the heat pump evaporator can be installed in the duct and the heat collectedcan be used to heat the incoming air or to pre-heat water used for other heating purposes. Since the internalair within a building is typically maintained to a set-point temperature throughout the year, ventilation heatrecovery systems tend not to be affected by seasonal variations in the same way that conventional ASHPs are.Medium and large buildings often have operations which produce waste heat. This can include plant rooms,server rooms and cafeterias. Installing a heat pump in these areas is a very effective method of collecting lowgrade heat that would otherwise be wasted, and transferring it at a higher temperature to areas where it isrequired, such as occupied areas or boiler feed water. The amount of heat that can be recovered and theassociated carbon saved will depend on both the amount of waste heat available and the availability of asuitable heat demand.DEHUMIDIFICATIONDehumidification is the process of reducing the amount of water in the air. It is sometimes employed in largerbuildings to improve the comfort conditions; to protect the building fabric, goods and materials from damageand mould growth; or for a specific drying process. Heat pumps are well suited to dehumidificationapplications as they can cool air down, thereby causing some of the water to condense out of it whilstabsorbing the heat energy to be used elsewhere.DOMESTIC HOT WATERHeat pumps can be used to produce domestic hot water for larger buildings; however there are issues whichneed to be carefully considered before using them for this application. Domestic hot water temperatures areusually held at 60°C or above to prevent the growth of Legionella in the water storage tanks. Although it ispossible to have output temperatures this high from a heat pump, it is likely to be operating at a low COP. Alsothe physical heating coils required to heat the domestic hot water need to be significantly larger than thoseused in conventional domestic hot water tanks. Some systems use heat pumps to pre-heat the incoming waterto around 45°C then use electric immersion heaters to further raise the water to the required temperature.
  • 19. Publication No Cu0179Issue Date: April 2013Page 16ADVANTAGES AND CONSTRAINTS OF USING HEAT PUMPS IN LARGER BUILDINGSThere are advantages and constraints to weigh up when considering the use of heat pumps over conventionalheating and cooling systems in larger buildings. These advantages and constraints are investigated in furtherdetail in the following sections.ADVANTAGESHEATING AND COOLING IN A SINGLE UNITBoth GSHPs and ASHPs can be used for heating in the winter and cooling in the summer. If fan coil units, airhandling units or chilled beams are used on the distribution system, then they can be utilised for both heatingand cooling, otherwise separate distribution systems need to be installed for the heating and cooling.There are capital savings to be made as only one system needs to be installed and maintained. There are alsosavings in terms of the plant room space required.Buildings with separate heating and cooling systems sometimes find themselves in a situation where the twosystems are operating at the same time in the same zone and the two systems end up working against eachother. This is very wasteful and can have a significant impact on energy bills. Having the heating and coolingsystems provided by a single unit helps to prevent this from occurring. Care should be taken when setting upthe controls for heat pumps capable of providing heating and cooling simultaneously.REDUCED MAINTENANCE COMPARED TO GAS BOILERSAlthough both heat pumps and gas boilers require maintenance to ensure their continued safe and efficientoperation, the maintenance requirements for heat pumps are less onerous. This is because the operation ofgas boilers is more complex and involves the combustion of gases, along with them having to withstand hightemperatures and pressures. Gas boilers also have fresh air requirements which often require ventilationsystems that themselves require maintenance.Compared to boilers, heat pumps used in larger buildings have fewer moving parts, are electrically poweredand so have no fresh air and flue requirements. This means that they have lower maintenance requirements. Itis important to note however that heat pumps used for cooling are included in Article 9 of EC Directive2002/91/EC on the Energy Performance of Buildings, which sets out a mandatory inspection regime for heatpumps over 12 kW. The purpose of the inspection is to assess the efficiency of the system and provideappropriate advice on possible improvement or replacement of the system. The inspections have to be carriedout by independent experts. In addition to this, heat pumps may require mandatory inspections under the EURegulation 842/2006 on Certain Fluorinated Greenhouse Gases, commonly referred to as the F-gasregulations. The purpose for these inspections is to reduce the likelihood of harmful greenhouse gases beingemitted to the atmosphere. The larger the heat pump, the more regular the inspections need to be. These F-gas inspections can be avoided by using heat pumps with refrigerants that are not included in the regulations.HIGHER EFFICIENCY THAN ELECTRIC RADIANT HEATERSElectric radiant heating systems are often used as a convenient heating system in areas which are not on themains gas network or where the use of gas is not practical. They do not require fuel deliveries, nor acombustion plant. The main disadvantage of electric radiant heating systems is that they are costly to run.Heat pumps, with their high SPF, provide the potential to significantly reduce the energy consumption ofelectrically heated buildings.For example, if a given building has a peak heat demand of 300kW, then it would require 300kW of electricalpower to keep it warm using electric radiant heaters. However, if a heat pump with a COP of 3 at theseconditions is used to heat the same building, then only 100 kW of electrical power is required.
  • 20. Publication No Cu0179Issue Date: April 2013Page 17RECOVERY OF WASTE HEATAs mentioned in the previous section, an advantage of heat pumps is that they have the ability to use lowgrade waste heat. For example, if a server room is emitting a constant out of heat at 25°C, this can be used bya heat pump to provide hot water at 55°C.CONSTRAINTSLOW OUTPUT TEMPERATUREAs discussed in the previous sections, heat pumps are typically restricted to providing output temperatures ofaround 50°C – 55°C. This means that they are unsuitable for retro-fitting onto older style heating systemswhich are designed for higher temperatures. This also means that the heat emitters used with heat pumpshave to be physically larger than those traditionally used in buildings. Building designers need to take this intoconsideration.Under floor heating systems are ideally suited to being used with heat pumps as they are designed to be usedwith low temperatures.REDUCED EFFICIENCIES WHEN LARGE TEMPERATURE DIFFERENCE BETWEEN SOURCE AND OUTPUTThe efficient operation of a heat pump is dependent on there being a relatively small difference intemperature between the heat source and heat sink temperature. This can lead to high costs and carbonemissions that are much higher than expected if the system is not correctly specified. If ASHPs are beinginstalled, it is particularly important to understand the heat pump’s performance across the whole heatingseason, as they are more susceptible to changes in the source temperature than GSHPs.Boilers and electrical heating systems are much less susceptible to these variations in outside temperaturethan heat pumps. It is important to take this into consideration when weighing up the relative benefits anddrawbacks of heat pumps compared to conventional heating systems.Where it is known that there is likely to be large changes in the source temperature, such as when ASHPs areused in colder countries, then it is recommended that a low temperature emitter is used, designed for use withoutput temperatures of 35°C – 40°C, rather than systems with 55°C output temperatures. This helps to reducethe efficiency drop on colder days.DIFFICULT TO RETROFIT TO OLDER BUILDINGSRetrofitting heat pumps to older buildings presents a number of challenges to overcome. First of all, thebuilding is likely to have been designed for heating devices at a higher temperature than is practical with aheat pump. The physical size of any radiators or heating coils will have to be bigger to overcome this issue,requiring more space. It may also require an upgrade of the building fabric to improve the air tightness andinsulation, especially around windows. This is because heat emitters with relatively high output temperatureare better at countering the cold draughts caused by poorly performing building fabric.When heat pumps with relatively low output temperatures are used with existing air handling units designedfor higher output temperatures, the air flow rates may have to be increased to maintain the same heat output.This may cause noise issues in the ducts, and may also cause cold draught complaints from people who have towork close to air outlet grilles. In order to overcome this, larger ducts and more air outlets may be required.There can be issues with retro-fitting a GSHP to older buildings with regards to installing the ground collectorpipework. This can involve disruptive excavation work on large areas of external ground, which may have anumber of existing services already buried in it. This is less of an issue when the heat pump is being installed aspart of the construction of a new building, as the work can be programmed as part of the ongoing exactionwork and the GSHP ground collector pipes can be coordinated with the other utility pipework and cabling
  • 21. Publication No Cu0179Issue Date: April 2013Page 18being installed at the same time. The local ground conditions should be assessed when looking to installground collector pipework, as excavating hard ground could be considerably more expensive than soft ground.The ground should also be scanned to detect if any existing services are buried in the location where thepipework is to be installed.
  • 22. Publication No Cu0179Issue Date: April 2013Page 19IMPROVING HEAT PUMP EFFICIENCYThere are a number of steps which can be taken to help in achieving the maximum efficiency from a heatpump installation when used with larger buildings. Some of these steps relate to the heat pump itself, andothers relate to the wider system with which the heat pump is used. The following section provides details ofthese steps and discusses how they can contribute to the overall efficiency of the heat pump system.USE HIGH EFFICIENCY COMPRESSORSThe compressor in a heat pump makes a significant contribution to the overall efficiency of the unit andtherefore it is important that a high efficiency compressor is used. Compressors for large buildings are typicallyeither centrifugal or scroll type compressors. Heat pump manufacturers often offer a choice in compressortype. In general, centrifugal compressors offer higher full load efficiency than scroll compressors. Howeverscroll compressors tend to maintain good efficiency when operated at part load, whereas the efficiency ofcentrifugal compressors tends to drop off more steeply at part loads. Scroll compressors also offer the abilityto operate between 0 – 100% of the full load, whereas centrifugal compressors are limited to being operateddown to around 20% of the full load. Therefore, if there is likely to be a constant load on the heat pump, thenit is more efficient to opt for a centrifugal compressor, but if there is likely to be a varying load, then a scrollcompressor may offer better overall efficiency. For smaller compressors (up to around 50 kW), reciprocatingcompressors are also an energy efficient option. Some larger heat pumps may have a number of smallercompressors in parallel to meet a wide range of demands.It is also important to specify premium efficiency9IE3 motors are used for the heat pump compressor. Onsome heat pumps the compressor and the motor are provided as a single sealed unit, but tends to berestricted to smaller sizes.REFRIGERANT CHOICEHeat pumps are available in a range of refrigerant choices. An ideal refrigerant will have a boiling point lowerthat the source temperature, be able to absorb a relatively large amount of energy during evaporation, haveappropriate densities in both the gas and liquid form, and require a relatively low operating pressure.Traditionally, a number of fluids used as refrigerants have been found to have a significant global warmingeffect and therefore have been banned. Fortunately, a number of refrigerants, including natural gases such asammonia and CO2, are commonly available. When specifying a heat pump, ensure that the refrigerant used iswell matched to the heat source and sink temperatures used in the building. Heat pump manufacturers canadvise on this issue.HEAT EXCHANGER SIZE AND MATERIALSHeat exchangers come in a range of sizes and configurations, however they all operate by passing one fluidacross another in order to transfer heat from one fluid to the other. The two fluids are separated by a thin,highly conductive material which allows the heat to transfer without any mixing of the fluids.The two main factors which aid the effectiveness of heat exchangers are the surface area separating the twofluids and the heat conductivity of the separating material. Although heat exchangers are available in a rangeof materials, copper is ideally suited to the task due to its high heat conductivity and its resistance to9The definition of a premium efficiency IE3 motor is specified in European Commission directive 2005/32/EC
  • 23. Publication No Cu0179Issue Date: April 2013Page 20corrosion. Aluminium is often used as a cheaper alternative to copper, but aluminium heat exchangers have tobe physically larger to provide the same heat transfer as the equivalent copper unit.In order to provide larger surface areas on heat exchangers, they can be provided with fins or ridges, althoughthis may cause cleaning to be more difficult.MATCH HEAT SOURCES AND SINKSHeat pumps are most efficient when the temperature difference between the heat source and the heat sink issmall. In order to facilitate this, efforts should be made to choose heat sources which are relatively warm andstable. For example, in colder climates, GSHPs should be selected in preference to ASHPs where possible. IfASHPs are used, then attempts should be made to place the evaporator in unexposed areas, such as in garagesor on the south facing side of the building where it is exposed to the direct sunlight during the day time.In terms of heat sinks, attempts should be made to provide low temperature emitters such as under floorheating rather than radiators. For cooling purposes, chilled beams are preferable to fan coil units and airhandling units as they have a higher working temperature.IMPROVE BUILDING FABRICImproving the building fabric will go a long way to creating a stable temperature within a building, which inturn will reduce the load on the heat pump and its running hours. The building should be as air tight aspossible to prevent warm air from leaking out and cold air coming in during the winter and vice versa in thesummer. This means having good seals around doors and windows. Cracks and unnecessary penetrations inwalls should also be sealed up. The walls and roof should have good insulation and the windows should beselected on their low heat loss properties. Ventilation systems should be fitted with heat recovery systems.South facing windows should be provided with blinds or shading to reduce summer cooling loads.USE INTELLIGENT CONTROLSEven the most efficient heat pump being used in a well-insulated building can waste significant amounts ofenergy without good controls. Larger buildings should always be separated out into discrete zones for thepurpose of heating and cooling. This will allow the supply of heating and cooling in unused areas to beswitched off completely. It also allows different areas to be maintained at different temperatures according tothe activities taking place within them. For example, areas where people engaged in physical activity can havea lower heating set point temperature than areas where people are working at desks.The controls should be configured to match the occupancy. Intelligent controls can learn to switch on the heatpump just in time for the start of the working day based on the external temperature. Therefore, on warmermornings, the heating would be switched on later than on colder mornings.With the appropriate heat pump, intelligent controls can make adjustments to the working pressure; thepressure is reduced when the source temperature is close to the sink temperature. This reduction in pressuremeans a reduced load on the compressor, which in turn results in lower energy consumption.
  • 24. Publication No Cu0179Issue Date: April 2013Page 21CONCLUSIONHeat pumps are a versatile and practical solution for heating and cooling larger buildings. They are available ina range of options. Before specifying a heat pump for a building, it is important to consider the followingfactors: Understand the heating and cooling demand for the building. For example, will there be a demand forheating above 55 °C which a heat pump might struggle to achieve? Or will there be a need forsimultaneous heating and cooling, which will necessitate at least two heat pump circuits? Can thebuilding be divided up into many separate zones for the purpose of regulating temperature? Decide on the most appropriate heating and cooling distribution system within the building. Forexample, under floor heating systems potentially have the lowest operating costs in the winter due tothe low output temperature, however they have a relatively high installation cost, are only suitablefor certain flooring types, and a separate cooling system needs to be installed. Air handling units, fancoil units and chilled beams have the benefit that they can be used for providing both heating andcooling. If using a low temperature heat emitter, be sure to consider the fresh air requirements andair change rates as the heat recovery times may be unacceptably long. Decide on a heat source. If using an ASHP, consider the effect that changes in the outsidetemperature is likely to have on the efficiency across the whole heating and cooling season.Remember that the COP of a heat pump reduces as the outside temperature falls. Beware of thestated performance of a heat pump as this tends to be based on an external temperature, of 7°C, asspecified in the EN 14511 test standard for heat pumps. If there are big changes in wintertemperature then consider using a two stage heat pump, or even a supplementary heating source tobe used on the very coldest days. If using a GSHP, consider if there is sufficient space to installhorizontal ground collectors or whether a local water course or borehole could be utilised. Ensure that the building is well insulated and air tight. Heat pumps are particularly susceptible to areduction in efficiency due to cold draughts entering buildings. Decide on a control philosophy for the building. Consider how different zones can be individuallycontrolled. Will there be any form of monitoring and targeting to ensure the continued efficientoperation of the system?Once all this has been decided, it is important to compare the life cycle cost and the carbon emission reductioncost with other alternatives. It is especially important to consider local factors, such as: Capital and labour costs, Building size and use, Available access to soft ground, aquifers or water courses, Fuel prices The carbon emission intensity of grid electricity Financial incentives for heat pumps (tax reductions, grants, special electricity tariffs, etcetera)When specifying the heat pump in order to minimise the whole life costs, ensure that the heat exchangermaterials, compressor, motor and refrigerant are selected on energy efficiency grounds rather than initialcapital costs.For new buildings in favourable climate, if care is given to selection, installation and operation, the differencein LCC (over 30 years) with traditional heating systems is reasonable. For GSHP, special attention should go to amitigation of the installation cost, for instance by combing the ground works with other ground works for thebuilding. For ASHP, the operating costs are more decisive and therefore special attention should go tooptimizing the design and installation for maximum efficiency. For good performing ASHP and GSHP with lowinstallation costs, the LCC is better than traditional heating systems. Financial incentives from the government
  • 25. Publication No Cu0179Issue Date: April 2013Page 22are good practice in order to improve the viability of many heat pump installations. With those incentives, theLCC of heat pumps should drop below that of traditional heating systems. Also, as heat pump technologyimproves with time and installation best practices are widely adopted then the LCC will continue to improve. Incolder climates and/or for renovation projects, the case for heat pumps needs to be assessed on the specificproject merits. In the right conditions heat pumps can be the right option for these buildings, or in some casesother heating systems are to be preferred from an economic point of view.