Heating system study for Cambrook House, Peasedown St John

Transcription

1 , Peasedown St John Final Report 26 April 2011 Centre for Sustainable Energy 3 St Peter s Court Bedminster Parade Bristol BS3 4AQ Registered company no t f info@cse.org.uk Registered charity no

2 This page is intentionally left blank

3 CONTENTS 1 Introduction Background Aim and scope of study Site details Description of site Heating system Controls Energy use Previous investigations Energy modelling Overview Energy use Energy cost Parent survey Conclusions and recommendations Annex A: NIBE system control settings proposed guidance for tenants...18 Centre for Sustainable Energy 3

4 1 Introduction 1.1 Background Cambrook House is a recent residential development located in Peasedown St John, near Bath. It was completed and occupied in August/September 2009 and consists of eight 1 bedroom self contained flats with communal areas. It forms part of a larger new build development of 25 homes with the remaining 17 homes being two and three bedroom houses. The eight flats in Cambrook House provide assisted living accommodation for young vulnerable adults with autism and are designed to promote independent living skills. The flats are owned by Ridgeway Care and managed by Flourish Housing Association, both members of the Aster Group. The scheme was commissioned by Bath & North East Somerset Council s Adult Care Service and the care provider is the National Autistic Society. The flats are compliant with 2006 Building Regulations and are therefore designed to meet certain carbon emission targets with good all round levels of energy efficiency. However, since Cambrook House has been occupied, there have been a number of issues associated with the operation of the exhaust air source heat pump (eashp) systems present in each flat. These systems provide space and water heating through a combination of ventilation exhaust air heat extraction and electric immersion heating. The issues have given cause for concern by residents and their parents, and are related to the following areas: a limited understanding of the user controls, which are significantly different to those of a conventional boiler system low thermal comfort experienced in some of the flats high electricity bills experienced in some of the flats A number of investigations to resolve these issues have already been undertaken by the Aster Group and several measures implemented. However, it has been agreed with the parents of residents that an independent study would be commissioned to evaluate and monitor the operation of the heating system. This report by the Centre for Sustainable Energy (CSE) therefore presents the results of that study and puts forward a series of recommendations that aim to address the heating problems being experienced by tenants. 1.2 Aim and scope of study The overall purpose of the study as set out in the project brief is to assess the existing heating system at Cambrook House and determine whether it is fit for purpose and value for money compared to alternative methods of heating. The specific objectives of the study are as follows: Evaluate the effectiveness and efficiency of the operation and costs of the current heating system in all individual flats and communal areas over a period of time, taking into account changes already undertaken by Aster Group Centre for Sustainable Energy 4

5 Assess the effectiveness of the current heating system to provide hot water heated to a satisfactory level Analyse information for other methods of heating, to include, but not be limited to, individual and communal gas heating, electric and oil fired heating, to produce comparative data on cost effectiveness Advise on the best ways to operate the existing heating system to ensure its efficiency and cost effectiveness Ensure the study is comprehensive and carried out successfully through liaison with relevant stakeholders as required by Aster Group. CSE originally proposed two levels of study for this project the first involving a site survey followed by desk based modelling and analysis, and the second covering the same but with the addition of an onsite technical monitoring programme. It was subsequently agreed to embark on the first option, and then review the outcomes in order to decide on the need for further monitoring work. 2 Site details 2.1 Description of site Cambrook House is a recent residential development located in Peasedown St John, near Bath. It was completed and occupied in August/September 2009 and consists of eight 1 bedroom self contained flats with communal areas. The two storey building contains four flats on each floor, with each flat having a floor area of 52 m 2. The layouts are similar in each and comprise of a living room, bedroom, kitchen/dining area, bathroom and hallway. The building forms part of a larger new build development of 25 homes, with the remaining 17 homes being two and three bedroom houses. These also use NIBE units but a different model to those in the Cambrook House flats; it is understood that the occupants are generally happy with the way these perform. The flats in Cambrook House provide assisted living accommodation for young vulnerable adults with autism and are designed to promote independent living skills. The flats are owned by Ridgeway Care and managed by Flourish Housing Association, both members of the Aster Group. The scheme was commissioned by Bath & North East Somerset Council s Adult Care Service and the care provider is the National Autistic Society. The development was built to 2006 Part L Building Regulations and achieved Code for Sustainable Homes Level 3, being the minimum standard required for new social housing developments at the time. 2.2 Heating system Each flat uses an exhaust air source heat pump system (NIBE Fighter 200P 3kW units) with under floor heating. These systems are designed for flats and single houses with small heating demands of about 2 4 kw and provide heating, hot water and ventilation. The heat pump element of the system is driven by a 550 W compressor and extracts heat from air drawn from ceiling vents in the kitchen and bathroom of each flat before venting to outside. The compressor will continue to operate and supply heat to the cylinders as long as the exhaust air (as taken from the kitchen and bathrooms) remains above 16 degc. The responsiveness of the system is slow compared to conventional boiler/radiator systems and heating up times can span a day or more. Centre for Sustainable Energy 5

6 The ventilation fan is permanently running regardless of the heat demand (unless the NIBE system is switched off) and will therefore provide continual ventilation at a minimum rate of 100 m 3 /hr. Fresh air is drawn into the flats via wall vents and gaps under the internal doors allow an adequate amount of circulation throughout the flat. The NIBE system stores domestic hot water within an integral cylinder; this is located within an outer jacket which, in turn, stores hot water for the underfloor heating system. Top up heat is supplied as required by a 3 kw electric immersion heater within the unit. As a minimum, the immersion heater is activated every 14 days to bring the cylinder above 60 degrees for Legionella protection. Along with a bath, each flat has an electric shower installed rated at 9 kw. An additional unit (but a different model to those in the flats) provides heat to the communal areas of the building. Hot water cylinder Immersion heater Outer jacket Figure 1: Schematic of the NIBE Fighter 200P 2.3 Controls The occupants of the flats are able to control the system by means of a control knob on the unit with four settings, and a standard room thermostat. There has been a notable lack of understanding among the tenants, parents and others on the function of the control knob and the meaning of the different settings. It is important to understand how these actually work and so the following describes the function of each setting in some detail. Centre for Sustainable Energy 6

7 The control switch on the NIBE unit has four settings (0 3) to activate different functions within the system. They are not specifically related to temperature. Figure 2: Schematic of the NIBE Fighter 200P Setting Function This turns everything off. There will be no heating or hot water, and the ventilation 0 will not be running. This means that the only ventilation in the flat will be through the vents in the wall, or from open windows. Only the heat pump is operational. The heat pump will provide heat, but if the air going in (as drawn from the kitchen and bathroom) falls below 16 C the heat pump 1 will stop providing heat (but the system will continue to ventilate) and the immersion heater will not switch on. The heat pump is operational and the immersion heater can provide top up heat if required. The immersion heater is now allowed to assist the heat pump if it is needed. Under this setting, the immersion heater will automatically supply heat if the heat pump alone cannot maintain the temperature required by the room thermostat. Additionally, if the air going into the heat pump (as drawn from the kitchen and 2 bathroom) falls below 16 C the heat pump will stop providing heat (but the system will continue to ventilate) and the immersion heater will then take over until the air temperature returns to 16 C, at which time the heat pump begins heating again. Note the point at which the system switches between Setting 1 and 2 is termed the bivalent point. Only the immersion heater is operational. The heat pump will stop providing heat (but 3 the system will continue to ventilate) and the immersion heater will now supply all the required heat. Table 1: NIBE unit control switch settings and function There are also some hidden settings on the NIBE unit that the user would not normally have access to. These include switches for selecting hot water priority and circulation pump function. 2.4 Energy use Electricity is the only fuel used at Cambrook House and weekly meter readings for each flat dating back to January 2009 have fortunately been taken by parents. A small number of readings have been slightly less or more than a week, but the data remains consistent in that all eight meters have always been read at the same time. Average weekly electricity consumption per month is shown in Figure 3 for each flat. Annual consumption during 2010 is shown in Figure 4 below. Note external temperature data is based on average daily values for the Severn Valley (Bath Area). Centre for Sustainable Energy 7

8 450 Average weekly electricity consumption per month [kwh/week] Flat 55 Flat 56 Flat 57 Flat 58 Flat 59 Flat 60 Flat 61 Flat 62 Figure 3: Average weekly electricity consumption per month Electricity Consumption [kwh] 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1, Flat No Figure 4: Annual metered electricity consumption during 2010 Also shown below in Figure 5 and Figure 6 are line plots of weekly consumption shown with average weekly external temperature. Four flats are each shown on two separate plots for reasons of clarity. Centre for Sustainable Energy 8

9 Weekly electricity consumption [kwh] Flat 55 Flat 57 Flat 61 Flat 62 Ext. Temp External temperature [Deg C] Figure 5: Flats 55, 57, 61 and 62 weekly electricity consumption shown with average weekly external temperature Weekly electricity consumption [kwh] Flat 56 Flat 58 Flat 59 Flat 60 Ext. Temp External temperature [Deg C] Figure 6: Flats 56, 58, 59 and 60 weekly electricity consumption shown with average weekly external temperature Centre for Sustainable Energy 9

10 During the period shown in the plots, the NIBE unit control settings were periodically changed. Although an accurate record of changes was not kept for the whole period, simultaneous adjustments in all flats were said to be as follows (dates are approximate): 5/12/10 all units in each flat switched to setting 2 13/01/11 all units in each flat switched to setting 1 20/01/11 all units in each flat switched to setting 2 22/02/11 all units switched to setting 1 with the exception of Flat 59 A number of conclusions can be drawn from the above charts. Annual electricity consumption for each flat in 2010 shown in Figure 4 ranges from 4,493 kwh (Flat 61) to 6,960 (Flat 62), with the other flats being spread fairly evenly between. To put this into perspective, the average annual domestic consumption in England for electricity in 2009 was 4,163 kwh 1. This figure obviously includes some electric heating use, but generally reflects the very large majority of homes having gas, oil or LPG heating, and so is indicative of average use for lighting, pumps/fans and appliances. Figure 5 and Figure 6 show that consumption levels are fairly consistent for all the flats during the nonheating season, but that relative to each other, there is a significant variation during the winter months. In particular, Flats 59, 60 and 62 appear to use significantly more electricity than the others. If hot water and lights/appliance use within each flat is assumed to be relatively constant year round, the differences seen in winter indicate that space heating would be the cause. The periods of significantly increased consumption for the three flats mentioned above appear to coincide with cold snaps in the weather i.e. when the external temperature drops close to zero Deg C or below. 3 Previous investigations In an attempt to resolve the issues of high fuel costs and heating controllability, a number of investigations and actions have already been undertaken by the Aster Group. These are noted as follows: An assessment of fitted carpets and their compatibility with under floor heating resulted in the removal of carpet underlay in some flats, including Flat 59 in March Additionally, some carpets were found to be causing a seal under the doors and hence disrupting the air flows that the heating system is designed to work with; Cowls were fitted to all the heating system vents in March 2010; New wireless thermostats were installed in each living room on 2/09/10. The original units were located in the hall of each flat; this was thought to be unsuitable as the halls experience higher temperatures than other rooms due to a relative concentration of underfloor heating pipes and low rates of ventilation. This resulted in the halls becoming too hot while the other rooms remained too cold; A new NIBE user guide has been produced and distributed in an attempt to clarify how the system works and how it is controlled; 1 Centre for Sustainable Energy 10

11 Hot water temperature restrictors at certain outlets have been removed; Temporary sub metering of the electricity supply to the NIBE units in Flats 58, 59 and 62 was undertaken along with internal and external temperature monitoring during Feb/Mar On reviewing this data as part of the current study, no significant conclusions could be made in regard of the problems under investigation. However, the average proportion of electricity consumed by the NIBE unit compared to the flats total consumption for the monitored period was found to be around 52%, 76% and 77% for Flats 58, 59 and 62 respectively. Although some of the above activities appeared to have successfully tackled specific problems, the consumption plots shown in Section 2, together with continued reports of inadequate levels of heating indicate that underlying problems still exist. 4 Energy modelling 4.1 Overview In order to help establish indicative energy demands and costs of the flats that could be expected according to their design and construction, and whilst under average occupation, modelling has been undertaken using NHER Plan Assessor software. 2 Four of the flats have been modelled, including the highest (62) and lowest (57) energy users, and two in between (55 and 61). Given that two of these flats are on the ground floor and two are on the first floor, any differences in energy use patterns due to location and orientation should be adequately represented. Aspects of the flats built form and heating system have been modelled as accurately as possible using details from architectural drawings and the SAP ratings undertaken at the design and as built stage. SAP and NHER outputs include modelled heat and electricity demands and annual fuel costs, which can be compared with metered usage to gain insight into how well the dwelling, and in particular the heat pump, is performing. It should be noted that there certain limitations to the modelling in that standard assumptions are used and variations in heating control preferences and appliance use, which may have significant impacts on overall electricity use, cannot be taken into account. 4.2 Energy use The table and chart below show the compares the results of modelling two scenarios against metered electricity use. Normal occupancy assumes the heating is on for 2 hours in the morning and 7 hours in the evening) while extended occupancy assumes 16 hours continuous heating per day and above average appliance use. As it was not possible to specifically include an exhaust air source heat pump as the heating system in the modelling, a standard air source heat pump was assumed, having a Coefficient of Performance (CoP) of SAP is the Government s Standard Assessment Procedure for the energy rating of dwellings and is based on the energy costs associated with space heating, water heating, ventilation and lighting (less cost savings from energy generation technologies). NHER (National Home Energy Rating) software is a suite of proprietary tools used to provide energy ratings (including the SAP) and energy analysis for dwellings. Centre for Sustainable Energy 11

12 Flat 2010 total metered electricity usage [kwh] Modelled NHER annual energy usage (normal occupancy including appliances) [kwh] Modelled NHER annual energy usage (extended occupancy including appliances) [kwh] 55 6,140 4,588 5, ,461 4,395 4, ,493 4,672 5, ,960 4,738 5,342 Table 2: Metered electricity use compared to modelled use 8,000 Annual electricity use [kwh] 7,000 6,000 5,000 4,000 3,000 2,000 1, total metered electricity usage Modelled NHER annual energy usage (normal occupancy including appliances) Modelled NHER annual energy usage (extended occupancy including appliances) Flat No. Figure 7: Annual metered electricity use compared to predicted use (modelled flats) Electricity Consumption [kwh] 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 Predicted consumption: (normal occupancy and averaged across all flats) Flat No Figure 8: Annual metered electricity use compared to average predicted use (all flats) Centre for Sustainable Energy 12

13 Electricity use for space heating [kwh/yr] Flat No Figure 9: Annual SAP space heating energy requirement Figure 7 shows that the predicted annual electricity consumption of the four modelled flats ranges from around 4,395 to 4,738 kwh, which is likely to represent the range of all eight flats. The small variation is mainly due to different space heating requirements resulting from the effects of orientation, exposure and solar gain. Figure 9 attempts to quantify this variation, which is minimal compared to the actual (metered) range of total electricity consumption across the flats, but indicates that the top floor flats (61 and 62) tend to have greater space heating requirements than those on the ground floor. This is because of greater heat loss through the roof i.e. they do not have a heated space above them. Figure 8 shows that the average predicted consumption across all eight flats corresponds to the lower range of actual metered consumption, such as that of Flats 56, 57, 58 and 61. This is in contrast to the other four flats (55, 59, 60 and 62) which appear to have significantly higher consumption compared to the average predicted figure. Given that flat 55 is on the ground floor and flat 62 is on the first floor, the results suggest that the difference in construction or increased exposure has little effect on energy use. The modelled Design Heat Loss across the flats ranges from 0.99 to 1.23 kw. In theory, if the 550 W heat pump compressor operates at a CoP of 2.5, gross heat output should be 1.38 kw (alongside the 3 kw immersion capacity), which should be more than sufficient to service the heat demand. 4.3 Energy cost Another element of the modelling was to assess the relative annual fuel costs if alternative heating systems were used. The same four flats were modelled with both gas and oil condensing combination boilers as the heating system, and modern electric storage heaters. The results are presented below: Centre for Sustainable Energy 13

14 Annual Fuel Cost [ ] Flat 55 Flat 57 Flat 61 Flat 62 Current heating system (based on metered data) Air source heat pump Gas combi boiler Oil combi boiler Electric heating (storage heaters) Figure 10: Comparison of modelled annual fuel costs assuming different heating systems Flat number Total annual fuel cost with current heating system (based on 2010 metered data) [ ] Air source heat pump Modelled NHER total annual fuel costs [ ] Gas combi boiler Oil combi boiler Electric heating (storage heaters) Table 3: Comparison of modelled total annual fuel costs assuming different heating systems Assumptions: Actual electricity tariffs and bills for all flats were not available so current heating system costs were based on an average electricity price of 13p/kWh Fuel costs assumed by NHER: heat pump elec costs p/kwh, gas 3.34 p/kwh, oil 6.06 p/kwh, elec heating 4.93 p/kwh off peak and p/kwh Normal occupancy and no secondary heating assumed Air source heat pump assumed Coefficient of Performance = 2.5 The results in Figure 10 and Table 3 show that the total annual modelled fuel costs (for space and water heating, lights and appliances) are all similar for a condensing combination gas boiler, air source heat pump and modern electric storage heaters. An oil boiler is notably more expensive, and the flats metered electricity costs (using an assumed tariff) range widely, with two flats (57 and 61) having similar costs to gas, air source heat pumps and storage heaters, and the remaining two flats having significantly higher costs than any of those modelled. Centre for Sustainable Energy 14

15 5 Parent survey In order to better understand the problems that the tenants and parents have been experiencing, and to explore how the controls have been used to date, a survey was undertaken with the parents. A brief set of questions was initially sent out and followed up with a telephone interview. Feedback was subsequently received from four of the parents relating to Flats 59, 60, 61 and 62, and is summarised below. The key concern is the lack of understanding and control that users currently experience with the system, which is exacerbated by the fact that several staff members may access the flats on a daily basis and potentially adjust the heating controls in addition to the tenants and parents; The lack of control is an issue across all the flats, regardless of their annual energy use. The key problems reported include excessively long warm up times, failing to achieve desired temperatures and low hot water flows; Parents have reported a poor understanding of the controls and the way the system works from the beginning, with little or no clear guidance issued; Confusion over the NIBE settings, particularly position 1 and 2, has been evident from the start, with some parents saying that they were told the system could be left on position 1; The session given on 20 th Jan improved general understanding, but parents were disappointed that such a session was not given much earlier, and soon after the tenants moved in. Additionally, it is evident that some parents remain confused over when to switch between setting 1 and 2. People now realise that setting 2 should be selected with the onset of cold weather and re set to 1 when the cold spell is finished. They don t, however, know exactly when to switch and at what external temperatures; The parents surveyed stated that, to their knowledge, window opening was minimal, with windows rarely opened in winter; Hot water use appears to vary significantly, with tenants taking baths, showers or a mixture of both, although most parents only have a general idea about frequency of use; Use of appliances seems to be relatively constant, with the common kitchen appliances, washing machines and TVs/computers all appearing to be used in similar ways; Secondary heating in the form of portable heaters e.g. oil filled radiators, electric panel heaters and fan heaters have been bought for some of the flats (including Flat 59, 61 and 62). These only tend to be used during severe cold spells; 6 Conclusions and recommendations In attempting to establish the nature, extent and cause of the reported problems at Cambrook House, this study has focussed on looking at metered energy consumption data, theoretical energy performance modelling of the flats and the experiences and practices of the tenants and parents. Discussions have also been held with Aster Group and representatives from NIBE. The following conclusions/recommendations can be made having assessed the desk based analysis along with the survey results: Centre for Sustainable Energy 15

16 Three of the flats (59, 60 and 62) are using significantly more electricity than the others during winter and this appears to be related to space heating. This is also reflected in total annual electricity use and cost, but there is an even spread between the highest and lowest consumers; Theoretical modelling of energy use shows that there is some variation between the flats in space heating requirements due to dwelling location (ground/first floor) and orientation (exposure and solar gain). A consequence of this is that the top floor flats tend to have greater space heating requirements than those on the ground floor. Although this will contribute to the higher winter consumption apparent in Flats 59, 60 and 62, other factors such as hot water, secondary heating and appliance use seem to have a greater effect and it is not currently possible to separately identify these; The size rating of the NIBE units would appear to be suited to the modelled Design Heat Loss of the flats; The key variables relating to the differences seen in electricity use throughout the monitored period are thought to include use of secondary heating systems and use of heating system controls (NIBE switch settings 1 or 2 and room thermostat). Although there is evidence that suggests hot water use (mainly electric shower and hot water for baths) is reasonably constant across the flats (as shown during summer energy use when there is no space heating requirement), variations in winter use may also have a significant impact. NIBE switch settings have been coordinated to a certain extent towards the end of the monitoring period, but there remains uncertainty over the use patterns of these other elements and their subsequent impact on electricity use; This recent coordination of NIBE control settings (i.e. position 1 or 2 ) seems to have improved comfort levels 3 but it is uncertain how this has impacted the variation in consumption across the flats; The point at which the NIBE control should be switched between 1 and 2 is difficult to predict with the modelling tools used for this study. However, whether or not the significant variation in consumption is related to this setting, the metered electricity data suggests that it starts to occur when external temperatures approach freezing point. Overall, the energy use analysis and modelling has suggested that these NIBE systems can potentially offer reasonable performance in terms of comfort levels and energy costs when their characteristics are well understood and they are operated correctly. However, it could be argued retrospectively that Cambrook House is not an ideal application for these units and that conventional systems with simpler controls would be more suited to the situation of the tenants, staff and parents; It is therefore recommended that: o o revised guidance is issued to the parents 4, which explains in clear terms how the system functions and how to operate the controls. The proposed guidance text is included as Annex A; a further training session is then held for both parents and other relevant staff to run through the guidance and answer any queries; 3 It is understood that these NIBE units are common in Sweden, where the long harsh winters require that they are run on Setting 2 for most of the year and that a higher energy use in winter is accepted in order to maintain comfort. 4 Since NIBE produced a Home owner user pack for the NIBE 200P, Fabia Pennington (a relation of one of the tenants) has also produced a guide on operating the system, which has been circulated to some, but not all, of the parents. CSE has therefore consulted with both Fabia and Giles Meredith (from NIBE) in producing the further guidance outlined in Annex A. Centre for Sustainable Energy 16

17 o coordination of all flats simultaneously switching between NIBE control settings 1 and 2 is continued, and an individual role is formalised with responsibility for monitoring weather forecasts and to communicate an early warning of when severe cold periods are due to begin and end; o should further investigation be thought warranted, specific monitoring of energy use is implemented on two of the higher energy use flats (e.g. 59 and 62) along with two of the lower energy use flats (e.g. 57 and 61). This should aim to monitor external and internal temperatures and distinguish and quantify electricity consumption between appliance use, NIBE hot water use and space heating. Such monitoring should ideally be for a one year period and is likely to be the only robust way to identify the sources of high consumption; Centre for Sustainable Energy 17

18 Annex A: NIBE system control settings proposed guidance for tenants Introduction This guidance aims to give an overview of the controls and settings on the NIBE Fighter 200P exhaust air heat pump as installed within the 8 flats at Cambrook House. These units, together with the underfloor heating systems, function very differently to conventional boilers and radiators. They also use different controls so the user must be confident in their operation to get the best out of the system and to ensure it works efficiently. To understand how the controls work, you need be familiar with the basic components of the NIBE unit and how it works. How the NIBE system works The system uses electricity to provide heating and hot water by means of an air source heat pump and an electric immersion heater, both of which are contained within the unit. The heat pump works by extracting heat energy from waste air drawn out of the property. This energy is used by the heat pump to generate hot water stored in the unit s integral cylinders. The heat is then fed back into the flat via the underfloor heating system or hot water for the taps. Some air source heat pumps take heat from the air outside the building (even on cold days they can extract some heat from this air), but the NIBE units are different they draw stale warm air in through the ceiling vents in the kitchen and bathroom and strip the heat from this air before pumping it outside. The air that is removed is continually replaced by fresh air coming in through the separate vents in the wall. This process provides continual ventilation for the whole flat 24 hours per day and the heating system is carefully designed to remove heat from this air flow and pump it back into the flat at the optimum rate to provide adequate levels of comfort for the tenant. The heat pump is very efficient at moving heat and uses a relatively small amount of electricity to do so in fact, this is just how a fridge works. However, during colder periods the heat pump on its own may not be able to supply enough heat to maintain a comfortable temperature in the flat. Additionally, it will not operate if the air it draws heat from is below a certain temperature (16 C). This is partly the reason why the NIBE unit also contains an electric immersion heater. This immersion heater acts as a boost to top up the heat supply to the flat and provide increased hot water if desired. Depending on the control setting, it will switch on automatically when needed. Put very simply, the heap pump is a more efficient way of providing heat than the immersion heater and so uses less electricity to produce the same amount of heat. In other words it is cheaper to run the heat pump than the immersion heater. However, the immersion heater is an essential part of the system as it is periodically needed to provide top-up heating, although its use will be minimised when the system is operated correctly. When compared to a conventional boiler and radiator system, an important point to remember with these systems is that the underfloor heating is much slower to respond to any required changes in room temperature. A period of several hours or more is often needed to achieve the desired change in temperature. For this reason, the system is designed to operate on a continuous basis and maintain a fairly constant temperature in the flat. Centre for Sustainable Energy 18

19 Heat pump control settings The control knob on the heat pump unit has four settings (0-3) to activate different functions within the system. They are not specifically related to temperature. Setting 0 This turns everything OFF. There will be no heating or hot water, and the ventilation will not be running. This means that the only ventilation in the flat will be through the vents in the wall, or from open windows. Only use this setting if the flat will be unoccupied for 10 days or more. If the occupant is away for shorter periods, simply turn the room thermostat down to 17 C. This means that the flat is not overly heated when there s no one at home and avoids the system being turned off and on again over short periods, which can lead to excessive electricity use and high heating bills. Setting 1 Only the heat pump is operational. The heat pump will provide heat, but if the air going in (as drawn from the kitchen and bathroom) falls below 16 C the heat pump will stop providing heat (but will continue to ventilate), the immersion heater will not switch on, and the flat will gradually lose all its heat. It is therefore important to avoid letting the bathroom and kitchen get too cold (below 16 C), so windows should not be left open. Setting 1 is the most efficient mode the system operates on. It should therefore be the default setting and used for most of the time provided the system can keep the temperature in the kitchen/bathroom to above 16 C, i.e. during the non-winter months. Setting 2 The heat pump is operational and the immersion heater can provide top-up heat if required. The immersion heater is now allowed to assist the heat pump if it is needed. Under this setting, the immersion heater will automatically supply heat if the heat pump alone cannot maintain the temperature required by the room thermostat. Additionally, if the air going into the heat pump (as drawn from the Centre for Sustainable Energy 19

20 kitchen and bathroom) falls below 16 C the heat pump will stop providing heat (but will continue to ventilate) and the immersion heater will then take over until the air temperature returns to 16 C, at which time the heat pump begins heating again. Setting 2 should be selected during and ideally one or two days before severe winter cold spells (i.e. when the external temperature looks likely to drop to 1 C or below) when both the heat pump and immersion heater are needed to maintain a comfortable temperature. As the system uses more electricity on this setting, the user should revert to Setting 1 as soon as the cold spell is over. Setting 2 can also temporarily be selected when more hot water is required than the system can normally provide when on Setting 1. Setting 3 Only the immersion heater is operational. The heat pump will stop providing heat (but will continue to ventilate) and the immersion heater will now supply all the required heat. Setting 3 activates emergency heating and should only be used if the heat pump is known to have failed. On this setting, the system will use significantly more electricity than usual and so the heating engineer should be contacted at the earliest opportunity. Indicator lamps A continuously lit top lamp on the front of the unit indicates that the heat pump is operating. A continuously lit bottom lamp on the front of the unit indicates that the immersion heater is operating. (Note - for a full description of these indicator lamps see the NIBE installation and maintenance instructions) Centre for Sustainable Energy 20

21 Adjusting the temperature settings The temperature in the flat can be adjusted by using the room thermostat, which should be located either in the hall or living room. Please read the instructions supplied with this unit to see how to go about doing this. Remember that this is a slow-response system meaning that a period of several hours is often needed to achieve the desired change in temperature. If the flat is too warm.. You can use the thermostat to turn the temperature down but avoid setting the temperature below 17 C as this could potentially cause the heat pump to shut down. Turn the room thermostat down to 17 C if the flat will be vacant for short periods (up to ten days). If the flat is too cold.. Before adjusting the thermostat, see if the heat pump is running by checking the top indicator lamp is continuously lit on the NIBE unit. If this is flashing and the main control knob is on Setting 1, it is likely that the air from the kitchen/bathroom is less than 16 C and the heat pump has therefore shut down. If this is the case, change to Setting 2 and the system will use the immersion heater to bring the flat back up to temperature. Once above 16 C, the heat pump will then automatically activate and provide lower cost heat. Only change back to Setting 1 when the outside temperature increases and there is little or no chance of the kitchen/bathroom dropping below 16 C. If the heat pump is running (the top lamp is continuously lit) then use the room thermostat to nudge the temperature up. As this is a slow response system, it is important to make small changes (1-2 C each time), and wait a few hours for the change to have an effect. You can monitor the room temperature from the display on the thermostat. It is often incorrectly assumed that a home will heat up more quickly by increasing the temperature setting in one large step and setting a higher temperature than you actually want e.g. 22 C instead of 20 C. This is not the case, and is likely to lead to overshoot where the thermostat shuts down the heat supply at the set temperature, but the heating system continues to give out residual heat for some time afterwards causing the room temperature to overshoot the set level. Centre for Sustainable Energy 21