None. Tim Pratt & Oliver Coe. Ronald Duyvestijn. Chris Durnford

Transcription

1 Prject title: Refrigeratin-based dehumidificatin: energy perfrmance and crpping effect n cmmercial nurseries Prject number: PE 013 Prject leader: Tim Pratt, Farm Energy Centre Reprt: Final reprt, April 2014 Previus reprt: Nne Key staff: Tim Pratt & Oliver Ce Rnald Duyvestijn Chris Durnfrd Lcatin f prject: Red Rfs Nursery (Nrthmr), E. Yrks Industry Representative: Nigel Bartle, Nrth Bank Grwers Ltd, Teesside Date prject cmmenced: 1 st December 2012 Date prject cmpleted 31 st March 2014 (r expected cmpletin date): Agriculture and Hrticulture Develpment Bard All rights reserved 1

2 DISCLAIMER AHDB, perating thrugh its HDC divisin seeks t ensure that the infrmatin cntained within this dcument is accurate at the time f printing. N warranty is given in respect theref and, t the maximum extent permitted by law the Agriculture and Hrticulture Develpment Bard accepts n liability fr lss, damage r injury hwsever caused (including that caused by negligence) r suffered directly r indirectly in relatin t infrmatin and pinins cntained in r mitted frm this dcument. Cpyright, Agriculture and Hrticulture Develpment Bard All rights reserved. N part f this publicatin may be reprduced in any material frm (including by phtcpy r strage in any medium by electrnic means) r any cpy r adaptatin stred, published r distributed (by physical, electrnic r ther means) withut the prir permissin in writing f the Agriculture and Hrticulture Develpment Bard, ther than by reprductin in an unmdified frm fr the sle purpse f use as an infrmatin resurce when the Agriculture and Hrticulture Develpment Bard r HDC is clearly acknwledged as the surce, r in accrdance with the prvisins f the Cpyright, Designs and Patents Act All rights reserved. AHDB (lg) is a registered trademark f the Agriculture and Hrticulture Develpment Bard. HDC is a registered trademark f the Agriculture and Hrticulture Develpment Bard, fr use by its HDC divisin. All ther trademarks, lgs and brand names cntained in this publicatin are the trademarks f their respective hlders. N rights are granted withut the prir written permissin f the relevant wners. [The results and cnclusins in this reprt are based n an investigatin cnducted ver a ne-year perid. The cnditins under which the experiments were carried ut and the results have been reprted in detail and with accuracy. Hwever, because f the bilgical nature f the wrk it must be brne in mind that different circumstances and cnditins culd prduce different results. Therefre, care must be taken with interpretatin f the results, especially if they are used as the basis fr cmmercial prduct recmmendatins.] Agriculture and Hrticulture Develpment Bard All rights reserved 2

3 AUTHENTICATION We declare that this wrk was dne under ur supervisin accrding t the prcedures described herein and that the reprt represents a true and accurate recrd f the results btained. Tim Pratt Technical Directr Farm Energy Centre Signature... Date... Andrew Kneeshaw Managing Directr Farm Energy Centre Signature... Date... Reprt authrised by: [Name] [Psitin] [Organisatin] Signature... Date... [Name] [Psitin] [Organisatin] Signature... Date... Agriculture and Hrticulture Develpment Bard All rights reserved 3

4 CONTENTS Headline... 5 Backgrund... 5 Summary... 6 Edible crp trials... 6 Ornamental crp mdelling... 8 Financial Benefits... 9 Tmat trials... 9 Ornamental crp mdelling... 9 Actin Pints Intrductin Materials and Methds Trial Site & Descriptin Mnitring and Data Cllectin Results Tmat cmmercial trials Ornamentals crp data cllectin and mdelling Financial impact Crp effect Capital cst Energy saving Discussin Cnclusins Knwledge and Technlgy Transfer Glssary References Agriculture and Hrticulture Develpment Bard All rights reserved 4

5 GROWER SUMMARY Headline Prtected edible crps Refrigerant based dehumidifiers trialled n a tmat nursery in 2013 delivered heat savings f 91kWh/m 2 (24%) cmpared t a cnventinal heating system. This was ffset by electricity use f 19kWh/m 2 and a 1kg/m 2 reductin in yield. Being a single year f trials with n replicates wrk in 2014 aims t investigate this yield lss. Prtected rnamental crps Extraplatin f data frm the trial t cver high energy rnamental crps grwn at 16 C r higher indicates that quicker paybacks may be pssible (less than fur years) due t a reduced dehumidificatin capacity requirement (lwer capital cst). Nurseries that use gas il fr heating shuld get a faster payback but this is ften ffset by the fact that such nurseries use relatively little heat. Backgrund Cntrlling the humidity in greenhuses is a vital part f grwing high-yielding, quality crps with the minimum use f crp prtectin chemicals. Traditinal methds f cntrlling humidity invlve venting warm, humid air frm the greenhuse whilst replacing this with clder, utside air which carries less misture. The cnsequential drp in temperature (lss f energy) is supprted using heat t maintain the required greenhuse temperature. We estimate that 20% t 40% f a nursery s annual energy cnsumptin is fr humidity cntrl. An alternative apprach is t remve the water vapur using a dehumidifier. There are a number f basic designs f dehumidifier; the mst cmmn being the refrigerant-based heat pump which has been used in this prject. The heat pump design is well prven and has fund many applicatins, e.g. grain drying and wd kilning fr instance, and trials have als been carried ut in greenhuses e.g. by ADAS at Stckbridge huse (Bartlett D.;1991). Early investigatin f the technique failed t result in significant cmmercial penetratin but advances in the technlgy and increased energy csts warranted this renewed investigatin. Agriculture and Hrticulture Develpment Bard All rights reserved 5

6 Summary Edible crp trials Trial set up Fur dehumidifiers (supplied by DryGair Ltd), with a cmbined water remval capacity f 180 litres/hur were installed in a 6,120m 2 greenhuse at Red Rfs Nursery Ltd in East Yrkshire. Over a grwing seasn, energy and crp perfrmance were cmpared t an adjacent, cnventinally heated and ventilated greenhuse cmpartment. The dehumidifiers were psitined half-way alng the crp rws and straddled the rws as shwn in the phtgraph belw. Warm, dry air is blwn ut frm all sides High humidity air is drawn in frm each side Figure 1. Dehumidifier in situ at Red Rfs Nursery Agriculture and Hrticulture Develpment Bard All rights reserved 6

7 Results After sme initial prblems with the dehumidifiers were reslved, they successfully perfrmed clse t specificatin extracting apprximately 45 litres/hur f water fr an energy input f 10kW f electricity i.e. 4.5 litres f water remved per kwh f electricity used. This figure is termed the Specific Misture Extractin Rate (SMER) and is a key figure when cmparing different manufacturer s equipment. Althugh the riginal expectatin was that they wuld nly be used when the humidity was at its highest, it was sn evident that savings were pssible in all but the lwest humidity cnditins (<65%). Therefre as lng as the RH was >65% and there was a heat demand in the greenhuse, the dehumidifiers were perated. The exceptin t this was when the heat prduced as a by-prduct f CO 2 enrichment met all f the greenhuse heat demand. As a result, the dehumidifiers were nt used frm week 25 t week 36. Figure 2 belw shws the weekly heat saving achieved. Figure 2. Abslute % (f ttal) weekly heat saving relating t use f dehumidifiers Between weeks 1 t 44 inclusive, the cntrl used 383kWh/m 2 f heat. The dehumidifier cmpartment used 91kWh/m 2 (24%) less and 19kWh/m 2 f electricity. One area f cncern was temperature unifrmity. With the fur dehumidifiers being, in effect, pint heat surces cmpared t the distributed pipe heating surce, ne might have expected sme degradatin in unifrmity. Hwever, measurements shwed there was Agriculture and Hrticulture Develpment Bard All rights reserved 7

8 actually a slight imprvement in temperature unifrmity, pssibly as a result f the fact that dehumidifiers have internal fans t prvide heat delivery and air mixing. The crp in the dehumidifier cmpartment yielded fewer tmates than the cntrl (1.0kg/m 2 ) as a result f the plants becming t vegetative arund week 11. Althugh the crp balance was crrected, the yield was nt recvered. The nursery s crp advisr was cnfident that this culd be avided in the future. This remains t be prven in HDC funded trials in 2014 (PE 013a) A majr plus pint relating t the crp is that n fungicide applicatins were required whereas the cntrl crp needed tw. Frmal disease mnitring was nt carried ut. Ornamental crp mdelling Data was cllected frm the pt chrysanthemum greenhuse at Duble H Nurseries t allw the impact f dehumidifiers t be calculated. We measured the amunt f time that heat was being used whilst the humidity was greater than 65%. Using this with the data recrded in the tmat trial we culd determine the likely perfrmance fr rnamental crp. Figure 3 belw shws the amunt f heat used (n dehumidifiers) and the likely heat saving if they had been used. The key figures are: Original heat use 261kWh/m 2 Heat saving 97kWh/m 2 Electricity used 19.5kWh/m 2 Figure 3. Ornamental crp: heat saving expected Agriculture and Hrticulture Develpment Bard All rights reserved 8

9 Cnsultatin with rnamental plant grwers suggests that n negative impact n plant grwth / yield is likely frm the use f a dehumidifier system. Financial Benefits Tmat trials Assuming, as advice suggests, the yield reductin experienced in 2013 culd be avided then it s fair t cncentrate n the energy saving ptential f the technique. The figures in Table 1 belw shw energy savings/inputs and are based n the premises that : All heat saved wuld have been prduced by a natural gas biler (68p/Therm) All electricity used wuld have been imprted frm the grid (7.0p/kWh) Nurseries that have CHP benefit frm lwer electricity csts which wuld increase the net saving by up t 0.40/m 2. Table 1. Edible: energy saving cst breakdwn kwh/m 2 /m 2 Heat saving (kwh/m 2 ) Electricity used (kwh/m 2 ) Net energy cst saving 1.14 The capital cst f an installatin fr an edible crp is in the rder f 10/m 2 giving a return n investment in nine years. Allwing fr the fact that ne mnth f savings were missed in the figures abve (equipment cmmissining delays) and that simple ptimisatin f the cntrl wuld increase perfrmance, a return n investment in six years appears pssible. Ornamental crp mdelling Advice suggests that n impact n crp yield r quality is likely with rnamental crps. Table 2 belw cmbines data cllectin frm a year rund high temperature rnamentals nursery with perfrmance data frm the tmat trial. The figure in brackets is the cst f heat if gas il is used (70p/litre). Agriculture and Hrticulture Develpment Bard All rights reserved 9

10 Table 2. Ornamentals: energy saving cst breakdwn kwh/m 2 /m 2 Heat saving (kwh/m 2 ) ( 7.36) Electricity used (kwh/m 2 ) Net energy cst saving 1.28 ( 5.99) Althugh net heating use is less fr rnamentals, the capital cst f an installatin fr an rnamental crp is als lwer, as the transpiratin and misture lad is reduced and less dehumidifier equipment is needed per unit area. Als, with n availability f free heat frm a biler which is being used t prduce CO 2, the dehumidifier heat can be useful all year rund. Taking these issues int accunt a return n investment in fur years is pssible (assuming natural gas as a fuel). We must als cnsider here the use f the system fr grwers wh are using gas il as their heating fuel. As this is mre expensive than gas, the payback n dehumidifiers lk even better. Hwever it s imprtant t realise that grwers wh use gas il are likely t be the nes grwing lwer temperature crps with lwer net energy cnsumptins. But even taking this int accunt and taking the example f a grwer wh is using a 1/3 f the energy shwn in the table abve, the return n investment might still be reasnable (pssibly three t fur years). The nly prvis t this is that ur mdelling has been dne n a dehumidifier running in a higher temperature envirnment (>16 C), and ne wuld expect the dehumidifier t perfrm less efficiently at lwer temperatures. Capital cst is clearly a key element in the ecnmics f a dehumidificatin system. As well as the hardware itself, the cst f prviding sufficient electrical pwer t the greenhuse is ften a significant issue. Hwever, this is site specific s hard t factr int a general ecnmic mdel. Agriculture and Hrticulture Develpment Bard All rights reserved 10

11 Actin Pints Edible crps The utcme f the 2014 trials will investigate if the 2013 yield reductin may be avided. Grwers are advised t delay adptin f the technlgy until such time as this is reprted Ornamental crps Dehumidifiers represent a viable energy saving ptin in specific circumstances. Any grwers using gas il t grw crps at 16 C r abve shuld cmpare their energy use t that f the rnamental crp nursery mnitred. Even if using 1/3 f the heat the return n investment is three years Grwers using natural gas shuld make the same cmparisn as abve. The impact f lwer energy cst and therefre savings ptential mean that dehumidifiers are nly likely t be financially viable fr high energy use crps. Agriculture and Hrticulture Develpment Bard All rights reserved 11

12 SCIENCE SECTION Intrductin Gd cntrl f humidity in greenhuses is a vital part f grwing high-yielding, quality crps as it ptimises grwth and minimises disease and the cnsequent use f crp prtectin chemicals. The nrmal methd f cntrlling humidity in a greenhuse invlves venting warm, humid air frm the greenhuse whilst replacing this with clder, utside air which carries less misture. The cnsequential lss f energy is supprted using heat t maintain the required greenhuse temperature. We estimate that 20% t 40% f a nursery s annual energy cnsumptin is fr humidity cntrl. An alternative apprach is t remve the water vapur using a dehumidifier. There are a number f basic designs f dehumidifier the mst cmmn being the refrigerant-based heat pump, and this is the ne which has been used in this prject. The heat pump design is well prven and has fund many applicatins e.g. grain drying and wd kilning and trials have als been carried ut in greenhuses e.g. by ADAS at Stckbridge huse (Bartlett D.;1991). Early investigatin f the technique failed t result in significant cmmercial penetratin. Hwever since then, there have been advances in the technlgy and energy csts are nw mre significant. S a renewed investigatin is justified. Sme internatinal cmmercial trials and applicatins by Israeli dehumidifier manufacturer (DryGair Ltd) and an ffer f equipment fr HDC trials in the UK helped t stimulate this prject. Ptential benefits f dehumidificatin are: A reductin in energy use and cst fr grwing Imprved yield due t reduced venting and therefre higher CO 2 levels Reduced fungal disease due t better humidity cntrl The trial bjective was t evaluate these whilst identifying any dwnsides f the technlgy. Agriculture and Hrticulture Develpment Bard All rights reserved 12

13 Materials and methds Trial Site & Descriptin Tmat - cmmercial trial The prject was carried ut n a cmmercial tmat nursery - Redrfs Nursery s Nrth Mr Lane in Cttingham, East Yrkshire. The test cmpartments used were Cmpartment 3 (CMP3) where the dehumidifiers were situated and Cmpartment 4 (CMP4) which was used as a cntrl. Each greenhuse was a typical duble Venl glass greenhuse structure with thermal screens and hanging gutters. CMP3 had a grwing area f 6,120m 2, CMP4 was 9,432m 2 ; all the data presented in this reprt is per m 2 t allw fr this difference in area. The mst fundamental difference between the cmpartments was that CMP3 had a vided thermal screen (1 in 10 strips missing) whereas CMP4 had a thermal screen with n strips missing. The crp grwn in bth cmpartments in 2013 was the mini plum tmat variety cv. Gurrincha. Yung plants arrived n the nursery in week 1 and crpping cntinued thrugh t week 45. Ornamentals data cllectin and mdelling Rather than carry ut additinal cmmercial trials, perfrmance data cllected frm the tmat trial was used with energy and climate data frm an rnamentals nursery t derive likely perfrmance figures; allwing the impact f dehumidifiers n energy use t be determined. The primary bjective was t prvide a strategic steer n whether rnamental specific trials might be financially viable. Data was cllected frm Duble H s nursery in New Miltn, Hampshire. The mnitred cmpartment was apprximately 18,000 m 2 and is a state f the art all year rund pt chrysanthemum greenhuse. Dehumidifier Equipment The dehumidifier units used in the trial were refrigeratin-based heat pump type dehumidifiers. With these, air is drawn ver the cling cil f a refrigeratin unit and its temperature is reduced t belw dew-pint. At this temperature water vapur starts t cndense frm the air. The cled air is then passed ver the ht cndenser cil picking up the energy lst in the cling/cndensing prcess s that it s humidity is nw lwer and its temperature is typically 6-8 C warmer than when it entered the unit. Agriculture and Hrticulture Develpment Bard All rights reserved 13

14 Belw is a simple schematic shwing the peratin f the units with the key indicative perfrmance figures: Figure 4. Refrigerant dehumidifier schematic This technlgy is well established in the heating, ventilatin and air-cnditining industry. Althugh applied in a different way, the principle f cndensing water n a cld surface t deliver humidity cntrl was used mst recently prir t this prject in clsed greenhuse prjects in the Netherlands. This was reviewed in HDC prject PC 256 (2007). An AFRC Institute f Engineering Research prject (Bailey B.J, Chalabi Z.S; 1989) and further wrk carried ut by ADAS at Stckbridge Huse (Bartlett D.; 1991) cnfirmed that the technlgy culd be applied t greenhuses. Hwever, at the time when energy csts were relatively lw, the savings did nt justify the investment required. The supplier f the equipment fr this prject, DryGair, has carried ut trials at the Vlcani Institute f Agricultural Research in Israel. Althugh published reprts are nt available, a Cefficient f Perfrmance (CP) f 8.0 has been quted (rati f heat saved t electrical energy in). If this culd be replicated in UK cnditins, the heat equivalent csts wuld be arund 0.78p/kwh (23p/Therm); cmpared t gas prices during 2013 f 2.22p/kWh (65p/Therm). The key specificatins f the equipment supplied were: Energy input 10kW f electricity Water remval rate 45 litres per hur Airflw 2 fans with a cmbined capacity f 40,000 m 3 /hr Agriculture and Hrticulture Develpment Bard All rights reserved 14

15 Accrding t the manufacturer a single dehumidifier is suitable fr 1,400m 2 f tmates. With CMP3 being 6,120m 2, DryGair chse t supply five dehumidifiers with a view t nly running fur if they prved t be adequate. The dehumidifiers were installed in a dmin pattern as shwn in Figure 5 belw. In practice fur were prven t be adequate. Dehumidifier Central path Figure 5. Dehumidifier layut The dehumidifier s design allwed them t straddle a rw f tmates whilst still allwing the crp wrk platfrm t pass. With rnamental crps being less leafy / transpiring less, the recmmended installatin density falls t ne dehumidifier fr 3,500m 2. Warm, dry air is blwn ut frm all sides High humidity air is drawn in frm each side Figure 6. Dehumidifier in situ at Red Rfs Nursery Agriculture and Hrticulture Develpment Bard All rights reserved 15

16 Mnitring and Data Cllectin Tw fundamental pints had t be determined fr UK grwers t make well-infrmed investment decisins abut this technlgy: The value f the net reductin in energy cst Heat saved minus electricity used Any effect n crp perfrmance Yield and fungal diseases T this end the fllwing data was cllected at the Red Rfs Nursery trial. Energy and dehumidifier perfrmance Heat used by each greenhuse cmpartment This was mnitred using nn-invasive flw meters and heat meter integratrs installed n the ht water supplies t each cmpartment. Electricity used by the dehumidifiers An electricity meter was installed n ne f the dehumidifiers and cnnected t the same data lgger as the heat meters. As all the dehumidifiers were turned n and ff tgether by the same cntrl equipment, the recrded energy was multiplied by the number f dehumidifiers t give ttal dehumidifier cnsumed energy fr the cmpartment. Dehumidifier perfrmance The key perfrmance indicatr fr a dehumidifier is the amunt f water remved frm the air fr each kwh f energy used. This is knwn as the Specific Misture Extractin Rate (SMER). The water recvered by a single dehumidifier (the ne with the electricity meter fitted) was drained int a sump. The vlume f water was measured using a calibrated pump that transferred the water int the irrigatin drain water cllectin system. The air temperature and humidity at the inlet and utlet f the dehumidifier were als recrded. These allwed the effect f air inlet cnditins n dehumidifier perfrmance t be determined. Anther useful perfrmance measure is the rati f useful heat prduced cmpared t electricity used. This is ften referred t as Cefficient f Perfrmance (CP). Hwever, a better practical measure f the dehumidifier CP is the amunt f heat saved per unit f electricity used; fr the purpses f this reprt we have referred t this as the dehumidifier CP. Agriculture and Hrticulture Develpment Bard All rights reserved 16

17 All the energy and dehumidifier data abve was recrded every five minutes by a data lgger which included a mdem allwing remte access t the data recrded. This enabled regular analysis and feedback in respnse t changes in the cntrl / peratin f the dehumidifier and the greenhuse climate. Greenhuse climate The greenhuse climate was cntrlled by a Brinkman cmputer. This enabled all the nrmal greenhuse climate and equipment status t be recrded; nce again in five minute intervals. Remte access t the Brinkman cmputer facilitated live climate analysis and set pint adjustments and dwnlading f the data fr further investigatin. The fllwing data were captured fr each greenhuse cmpartment: Aerial envirnment Temperature Humidity RH and HD CO 2 cncentratin Equipment status Heating pipe temperature Vent and thermal screen psitin Dehumidifiers n/ff (CMP3 nly) Weather data Light level Outside temperature Simple battery pwered data lggers were als laid ut in a grid pattern in each greenhuse cmpartment t recrd the effect f the dehumidifiers n temperature unifrmity. Agriculture and Hrticulture Develpment Bard All rights reserved 17

18 Crp data Crp registratin data was cllected by the nursery every week, under the guidance f their advisr (Rnald Duyvesteijn). The data cllected was: Fruit set per m 2 Crp balance Fruit size (visual) Leaf length Truss length Truss height Yield kg/m 2 Frmal disease mnitring was nt carried ut. Feedback frm the grwer (Chris Durnfrd) and visiting tmat study grups was hwever nted. Ornamental nursery data cllectin The fllwing data (recrded every 5 minutes) was exprted frm the nursery s climate cntrl cmputer: Heating pipe temperature Vent and shade screen psitin Greenhuse temperature and relative humidity Energy data cllected included: Gas used by the biler weekly meter readings Heat used heat meter cnnected t a GSM enabled data lgger Agriculture and Hrticulture Develpment Bard All rights reserved 18

19 Results Tmat cmmercial trials Key dates / changes Week 1 yung plants arrive frm the prpagatr c.v. Garrincha, pinched and grafted n Maxifr. Starting density 2.86 heads/m 2 Week 5 cmmissining/testing f equipment Als secnd sht taken, increasing the density t 4.3 heads/m 2 Week 6 dehumidifiers turned ff T benchmark greenhuse cmpartment energy use Week 7 dehumidifiers set t run when the HD was less than 3.5g/m 3 Week 8 dehumidifiers set t run 19:00-16:00 all days (n humidity based cntrl) T allw the dehumidifiers t wrk hard and accelerate the understanding f their peratin Week 15 cmpressr replaced n a single dehumidifier Due t pr perfrmance Week 16 dehumidifier cntrl based n HD and vent psitin Turned ff when the HD > 3.5m 3 AND the lee side vent was >10% pen T avid running the dehumidifiers when there was n benefit Week 24 dehumidifiers turned ff Due t lw heat demand and the need t burn natural gas fr CO 2 enrichment satisfying all the heat demand Week 37 - dehumidifier cntrl based n HD and vent psitin Due t increasing heat demand and reducing CO 2 demand Week 45 end f crpping Agriculture and Hrticulture Develpment Bard All rights reserved 19

20 Dehumidifier perfrmance Specific Misture Extractin Rate (Litres f water remved per kwh f electricity used) Figure 7 shws the SMER thrugh the year. Dehumidifiers perfrm better with higher temperature, higher water cntent air. Therefre, a gradual imprvement was expected as the crp gt bigger and the challenge f maintaining acceptable humidity cnditins within the greenhuse increased. Althugh the graph shws the average perfrmance each week, the data cllected allwed shrter perids (a few hurs) f peratin t be analysed. This allwed the dehumidifier perfrmance under ccasinal ideal cnditins t be determined relatively early in the prject and indicated that SMER was nt up t specificatin. The cause was fund t be a prblem with the cmpressr which was replaced in week 15. The impact f this is demnstrated by the step imprvement in perfrmance in week 16. Fllwing this, the dehumidifier perfrmed at/arund its specificatin. The dehumidifier was turned ff during the summer; hence n data fr this perid is shwn. Figure 7. Dehumidifier perfrmance as litres f water extracted per kwh f electricity Agriculture and Hrticulture Develpment Bard All rights reserved 20

21 Dehumidifier CP This is the rati f heat saved vs. electricity used. The relatively pr perfrmance during the early weeks was due in part t lw greenhuse humidity (small, plants, lw utside temperature) and the cmpressr prblem previusly discussed. The impact f the frmer was exaggerated by the unseasnably cld weather during weeks in particular. The CP frm week 37 nwards appears abnrmally lw especially when the litres/kwh data fr the same perid were similar t the weeks leading up t the summer shutdwn. Late in the crpping year there were differences in the crp that may have cntributed t this apparent pr perfrmance but this was nt prven. A CP f 5.0, reducing t 4.0 by week 45 was expected rather than the achieved average f 3.0. Figure 8. Dehumidifier CP Dehumidifier running hurs The dehumidifiers ran fr a ttal f 3,411 hurs during the 2013 crpping year. Excluding the summer perid when they were turned ff, they were used fr an average f 19 hurs / day. Agriculture and Hrticulture Develpment Bard All rights reserved 21

22 Figure 9. Dehumidifier running hurs Energy data The greenhuse cmpartments were nt identical and were therefre likely t use different amunts f heat even when perated in the same way withut dehumidifiers. T assess the underlying difference, the dehumidifiers were nt run during week 6 and the heat used by each cmpartment was cmpared. On average, CMP3 (cntaining the dehumidifiers) used 6% mre heat than CMP4 (cntrl). All the data that fllws was crrected t take accunt f this difference t facilitate a direct cmparisn. Prir t the trial, we pstulated that the dehumidifiers wuld nly deliver savings when the humidity was high. In such instances they wuld be used as the first line f actin t lwer humidity i.e. befre gapping the screen, pening the vents r increasing the minimum heating pipe temperature. During the early weeks f the trial the dehumidifiers were, in effect run n a timed basis (19:00-16:00). The ff hurs cincided with bth high electricity prices and when a rapid drp in greenhuse temperature was required fr the pre-night temperature strategy. The reasn fr running them such lng hurs when there was ptentially n benefit was t prduce data s we culd learn abut their characteristics quicker. We relied n the underlying physics f the prcess t prvide immediate feedback: Ttal heat utput cmprised tw elements Heat recvered = the energy released by cndensing the amunt f water prduced in 1 hur Electrical energy input via the cmpressr and fans Agriculture and Hrticulture Develpment Bard All rights reserved 22

23 Valuing the heat prduced at the equivalent cst f prducing it frm a biler vs. the cst f electricity used gave a simple is it wrth running answer. Prir t the faulty cmpressr being identified, ur assumptin n ecnmic peratin was crrect. Hwever, nce the cmpressr was repaired the data suggested that running the dehumidifiers at lwer humidity s culd als deliver savings. Experience with this prject has led us t cnclude that dehumidifiers can be run ecnmically : Whenever there is a heat demand But NOT When the greenhuse humidity (RH) is especially lw as the ability t remve water is restricted and the efficiency f the dehumidifier is pr. The cut-ff humidity belw which the dehumidifier shuld be turned ff depends n many factrs but as a guide an RH f 65% r less seems sensible Figure 10 belw details the weekly heat and electricity use and each cmpartment. Figure 11 verleaf details the amunt f heat saved each week. Figure 10. Weekly energy use When the dehumidifiers were nt used, CMP3 used mre heat than CMP4 especially between weeks 25 t 30. This is even thugh the heat use data was crrected fllwing the benchmarking adjustment as described earlier in this reprt. This was, in part, due t tuning set pints in CMP3 after turning ff the dehumidifiers. Frm week 31 nwards there was Agriculture and Hrticulture Develpment Bard All rights reserved 23

24 little difference in heat use. When calculating the heat saving, zer saving was assumed fr weeks 25 t 36 Figure 11. Weekly heat saving in the dehumidifier cmpartment cmpared with the cntrl cmpartment Table 3 belw summarises the ttal amunt f energy used / saved ver the whle crpping year frm weeks 1 t 44 inclusive. As heat data was nt available fr week 1-4 a figure f 11kWh/m 2 was assumed fr bth cmpartments during this perid. Table 3. Ttal energy use Heat used (kwh/m 2 ) Electricity used by dehumidifiers (kwh/m 2 ) CMP3 (dehumidifiers) CMP4 (cntrl) Difference 91 (24%) 19 This gives a whle f seasn dehumidifier CP f 4.8, including a perid when the dehumidifier was nt perating crrectly. Agriculture and Hrticulture Develpment Bard All rights reserved 24

25 It is wrth nting that CMP4 used the equivalent f 450 kwh/m 2 f gas (assumed biler efficiency f 85%). This is already a lw figure cmpared t mst tmat nurseries; making a further reductin f 91kWh (gas equivalent) even mre significant. Greenhuse climate Humidity Dehumidifiers enabled humidity cntrl t g further than wuld have nrmally been the case with using heat venting. As energy savings were pssible in all but the highest HD cnditins (lw RH), it was ratinal t use the dehumidifiers t achieve energy savings in these cnditins. As such lwer verall humidity cnditins were achieved in the cmpartment with the dehumidifiers. Lking at the average weekly daytime HD achieved (figure 12), this effect was relatively small especially between weeks 20 t 24. Even thugh the dehumidifiers did run during the daytime their water remval capacity (294 litres / hur / Ha) was relatively lw cmpared t the transpiratin f the crp. The pr perfrmance f the dehumidifiers early in the year likely lst any difference there wuld have been befre they were repaired in week 15. Figure 12. Average daytime humidity deficit With the crp transpiring much less vernight the dehumidifiers had a bigger impact n the night time HD achieved (figure 13). Agriculture and Hrticulture Develpment Bard All rights reserved 25

26 Figure 13. Average night time humidity deficit CO 2 With the dehumidifier achieving a slightly better HD during the daytime in CMP3 with less venting better CO 2 levels might be expected. Hwever, as previusly discussed in relatin t the impact n daytime HD, their impact n daytime HD levels and therefre venting was relatively small. In additin, their greatest impact n venting tended t be when the daily heat demand was still high and therefre CO 2 supply was nt a limiting factr. Overall, the dehumidifiers had n measurable impact n the daytime CO 2 level achieved. The dehumidifiers did hwever have a ntable impact n the night time CO 2 level. This ties in with mre screening hurs and less gapping / venting vernight. Althugh the night time CO 2 level has n direct cnsequence / impact n yield, there was thught t be a ptentially negative impact thrugh the greater retentin f flue gas pllutants such as NO x and ethylene. Thermal screen peratin With the dehumidifiers running almst all the time when the thermal screen was clsed, and delivering a better humidity cntrl, the screens were gapped less and clsed fr lnger cmpared t CMP4 (figure 14). Over the whle crpping year the screens in CMP3 were clsed fr 2,091 hurs cmpared with 1,867 hurs in CMP4 (12% mre). Agriculture and Hrticulture Develpment Bard All rights reserved 26

27 Figure 14. Thermal screen hurs Temperature unifrmity An area f cncern with the dehumidifiers was their pssible adverse impact n temperature unifrmity. We cnsidered that, as a less distributed frm f heat, reginal areas f higher temperature might be evident. Figure 15 belw shws the average temperature achieved n a grid f 15 data lggers ver a 3 day perid in February when the dehumidifiers were turned ff. Figure 16 shws data frm the same lggers under cmparable cnditins ne week later when the dehumidifiers were turned n. With the dehumidifiers ff the highest temperature was 1.9 C abve the average and the lwest was 2.0 C belw the average. With the dehumidifiers n the highest temperature was 0.4 C abve the average and the lwest was 1.7 C belw the average. This result was validated / cnfirmed by cmments frm the grwer pertaining t the cmparative evenness f the crp cmpared with previus years. Agriculture and Hrticulture Develpment Bard All rights reserved 27

28 Figure 15. Temperature unifrmity: dehumidifiers ff Figure 16. Temperature unifrmity: dehumidifiers n Agriculture and Hrticulture Develpment Bard All rights reserved 28

29 Crp data The fllwing data fcusses n the perid up t week 28 and was cmpiled by the nursery s crp advisr Rnald Duyvestijn. After this date ther factrs, principally pests and flue gas pllutants, affected crp perfrmance and made any ptential cmparisn misleading. Fruit set Fruit set was almst equal in the tw cmpartments at the start f the seasn but then tended t be wrse in the dehumidifier treatment during weeks 10 t 16 when the dehumidifiers had their greatest impact n the greenhuse climate (mst ntably HD). This trend reversed between weeks 15 and 20. During this whle perid dehumidifiers treatment set a ttal f 1,936 fruit and the cntrl set 1,886 fruit (figure 18). Figure 17. Fruit set per week Agriculture and Hrticulture Develpment Bard All rights reserved 29

30 Figure 18. Ttal fruit set Fruit size Althugh nt measured specifically fr this trial, measurements in the cntrl treatment gave an average fruit weight f 12g. The fruit size in the dehumidifier treatment was ften visually less. Althugh the fruit set was higher, the quality f fruit set in the dehumidifier treatment was nt as gd. Leaf length Between weeks 7 t 10 the leaf length in the dehumidifier treatment was shrter, pssibly caused by the lwer humidity in that cmpartment (figure 19). Arund week 11 this pattern reversed and althugh the trend was fr shrter leaves, the leaf length in the dehumidifier treatment was always lnger. Lnger leaves suggest a mre vegetative grwth habit. Agriculture and Hrticulture Develpment Bard All rights reserved 30

31 Figure 19. Leaf length Truss length Shrt truss length indicates larger fruit and a mre generative grwth habit. The trend was similar t the leaf length with a ntable change in week 11. The lnger truss length was in line with the visually smaller fruit size seen at the same time. Figure 20. Truss length Agriculture and Hrticulture Develpment Bard All rights reserved 31

32 Truss height There was n clear difference between the treatments. Figure 21. Truss height Yield The ttal yield up t week 30 was 17.2kg/m 2 in the dehumidifier treatment and 18.2kg/m 2 in the cntrl (figure 22). This difference ccurred mainly between weeks 17 and 20. These fruit were set between weeks 10 t 14. This cincides with the mre vegetative trend in the crp nted in the leaf length and truss length at the same time. Lking mre clsely at the yield between weeks 21 t 30, the ttal was 11.68kg/m 2 in (dehumidifier) and 11.66kg/m 2 (cntrl). The fruit harvested in this perid were set when the plants were equally in balance in bth cmpartments and dehumidifiers had a rapidly diminishing impact n the greenhuse climate. Agriculture and Hrticulture Develpment Bard All rights reserved 32

33 Figure 22. Yield Disease Frmal disease mnitring was nt carried ut. Hwever, the clearest indicatin f the impact f dehumidifiers n fungal disease such as Btrytis was the nursery s spray recrds. Cntrl cmpartment (CMP4) tw fungicide applicatins; ne in early May and ne in early Octber. Dehumidifier cmpartment (CPM3) n fungicide applicatins. Albeit smewhat infrmal, tmat study grups that visited the nursery during 2013 agreed that disease levels in CMP3 were lwer than in CMP4. Summary f crp data / effects: The dehumidifiers had a mre vegetative effect n the plants. There was n effect n the ripening speed; as the prductin started in bth cmpartments at the same time. The fruit size was smaller. The ttal fruit set was higher. The ttal prductin was 1 kg/m 2 less. Agriculture and Hrticulture Develpment Bard All rights reserved 33

34 The prductin lss ccurred between weeks 7 and 20. This was related t a very vegetative trend perid in the plants in the dehumidifier cmpartment. T avid the lwer yield a mre generative plant shuld be created early in the year. Ornamentals crp data cllectin and mdelling Analysis f data cllected Energy Figure 23 shws the amunt heat used each week by the greenhuse. This served as the benchmark against which savings were calculated. The ttal amunt f heat used p.a. was 261 kwh/m 2. Figure 23. Ornamental crp heat use Greenhuse climate predictin f dehumidifiers peratin As mentined previusly, energy savings can be achieved even when the humidity is deemed t be acceptable. The saving achieved is hwever affected by the amunt f water in the air; a lwer RH resulting in a lwer saving. In additin, a lwer air temperature but high RH will result in a lwer saving as the amunt f water held in the air (abslute humidity) is lw, limiting the latent energy that can be recvered. Frtunately, the temperature in bth the rnamental and tmat greenhuses were bradly similar leaving the humidity as the key difference. Agriculture and Hrticulture Develpment Bard All rights reserved 34

35 T determine the dehumidifier running hurs with the rnamental crp the fllwing cntrl strategy was applied. The dehumidifier was deemed t have been running if: The heating pipe temperature was abve a set threshld Ensuring that it nly runs when a heat saving wuld have been achieved The RH was abve a set threshld Ensuring that it nly runs when it s efficiency is acceptable Figure 24 shws the predicted daily length f dehmidifactin peratin time fr RH and pipe temperature threshlds f 65% and 30 C respectively. In this situatin the dehumidifiers wuld run fr 6,491 hurs p.a. Figure 24. Ornamental crp run regime mdel The mdelled impact f increasing the RH threshld t 70% (the main driving factr) was relatively small, reducing the ttal hurs t 6,401 hurs p.a. (1.4% less). Dehumidifier CP Multiplying the dehumidifier running hurs by pwer rating (kw) gives the ttal kwh f electricity used. Multiplying this by the dehumidifier CP gives the amunt f heat saved. CP data frm the 2013 tmat trial is slightly misleading due t the cmpressr prblem early in the year. Hwever, with the prject being extended int 2014, mre recent data allwed a better assessment f the true CP. Figure 25 shws the CP trend used t calculate the ptential savings. Agriculture and Hrticulture Develpment Bard All rights reserved 35

36 Figure 25. Ornamental crp: CP expected Energy saving Cmbining all the infrmatin abve prduces the data frming Figure 26 belw. The mdel prduces a ptential anmaly arund week 30 in particular; the impact f the dehumidifier seems disprprtinately lw. Hwever with energy used in this perid being small and cnsidering the limitatins f the mdel, the effect n indicated annual perfrmance is deemed insignificant. The prjected annual energy data were: Heat saved 97kWh/m 2 (37%) Electricity used 19.5kWh/m 2 Figure 26. Ornamental crp: calculated heat saving relating t use f dehumidifiers Agriculture and Hrticulture Develpment Bard All rights reserved 36

37 Financial impact Crp effect A lwer yield was recrded in the tmat trial in Hwever, advice suggests that this can be reslved and this is being scrutinised in the 2014 trial. N such effect is expected n rnamental crps. The figures that fllw assume n crp related benefit r lss. Capital cst The current list price f the equipment supplied by Drygair is 17,000 per unit. Nrmal purchasing discunts plus the pssibility f cmpetitin in the market culd reduce the price dwn t arund 14,000 per unit. The cst t install the dehumidifiers can be significant. One area that culd be verlked is the cst f prviding electricity t each unit. This cmprises bth cabling within the nursery plus the pssible need t reinfrce the grid cnnectin t a nursery. Bth are relatively unique t a specific site. Fr the purpses f the fllwing calculatins we have assumed: Tmat crp (bradly applicable t all high temperature edible crps) 6 dehumidifiers per Ha ttal cst 84,000 Electrical installatin including cntrls - 15,000 Ttal installed cst 99,000/Ha ( 9.90/m 2 ) Ornamental crp 3 dehumidifiers per Ha ttal cst 42,000 Electrical installatin including cntrls - 10,000 Ttal installed cst 52,000/Ha ( 5.20/m 2 ) Agriculture and Hrticulture Develpment Bard All rights reserved 37

38 Energy saving Cst f electricity used Red Rfs Nursery benefit frm having CHP. In 2013, the average cst f electricity used was arund 6.0p/kWh. If the electricity was all imprted frm the grid the average wuld be in the regin f 7.0p/kWh. Value f the heat saved With Red Rfs having CHP it culd be argued that the heat saved is wrth less than if it had been prduced by a biler. Hwever, the CHP rarely satisfied all f the heat demand s the heat saved by the dehumidifiers wuld have reduced biler peratin in mst instances. Fr the purpses f this assessment, prices bradly indicative f thse in 2013 were used (assumed biler efficiency f 85%): Natural gas 2.7p/kWh (68p/Therm) Cst f electricity Imprted frm the grid 7.0p/kWh Frm CHP 6.0p/kWh Gas il 7.5p/kWh (70p/litre) Table 4 belw shws detailed results fr each scenari cnsidered. Table 5 shws the net financial saving. Table 4. Energy saving cst breakdwn relating t use f dehumidifiers High temperature edible crps Ornamental crp Heat saving (kwh/m 2 ) Electricity used (kwh/m 2 ) Value f heat saved (natural gas) Value f heat saved (gas il) Cst f electricity used (CHP) Cst f electricity used (100% imprt) Agriculture and Hrticulture Develpment Bard All rights reserved 38

39 Table 5. Energy saving summary Saving /m 2 High temperature edible crps Ornamental crp Natural gas heat surce / CHP electricity Natural gas heat surce / 100% imprt electricity Gas il heat surce / CHP electricity Gas il heat surce / 100% imprt electricity Edible crps In practice mst nurseries have natural gas. In this case the simple return n investment wuld be 9 years based n the trial results as measured. Hwever, with experience gained during this prject additinal savings f 30kWh/m 2 seem pssible. This wuld bring the simple return n investment dwn t 6 years. Ornamental crps Very few (if any) rnamental nurseries in the UK have CHP i.e. all electricity used wuld be imprted frm the grid. Furthermre high energy rnamental crps tend t use natural gas. Therefre a saving f 1.28/m 2 is mst likely t apply t high energy rnamentals nurseries. This being the case, a simple return n investment in 4 years is expected. Due t the cst f gas il, rnamental nurseries that use it tend t grw lwer energy requirement crps. Therefre the ptential energy saving (kwh) will be les; s the cmparisn in the abve table is less likely t ccur in practice. In this situatin, a simple pr-rata f the savings based n ttal current heat use cmpared with the data frm Duble H Nurseries is useful. Fr example, if a nursery used 1/3 f the heat p.a. the savings wuld be in the rder f 1/3 ( 1.82/m 2 ). Even s, with the high cst f gas il the simple return n investment wuld then be 3 years. Agriculture and Hrticulture Develpment Bard All rights reserved 39

40 Discussin Tmat trial Energy Albeit cmprmised t sme degree by pr perfrmance f the dehumidifiers early in the trial the ttal heat saving achieved was still significant (22%). Interestingly, this is f a similar magnitude t the first year savings btained when thermal screens were first trialled in the UK (PC 198, 2003) and thermal screens are nw accepted as standard equipment in a mdern glasshuse. With the experience gained during 2013 it is als clear that savings culd have been realised befre week 7 when the dehumidifiers were nt used in Additinally, the unusual cld March and April in 2013 will have resulted in smaller savings than wuld have been btained in an average year. There is therefre little dubt that energy savings recrded fr the tmat crp in 2013 can be beaten. A target saving f 100kWh/m 2 seems realistic. Beynd the impact f the dehumidifiers in islatin, they have ptential t change ther aspects f greenhuse cnstructin/equipment. The mst bvius is thermal screens where there is ften a cmprmise between energy saving and humidity cntrl. There is a particular fcus by thermal screen manufacturers n develping materials that are well sealed with regard t air exchange but that have an inbuilt wicking actin t allw misture t pass thrugh them. Hwever, even allwing water vapur t pass thrugh is allwing energy t be lst. Dehumidifiers bth remve the need t allw misture t pass thrugh screens, thereby allwing higher energy saving materials t be used, and recver the energy cntained in the water vapur. This prvides the pprtunity fr a secnd tier f energy saving thrugh the use f different thermal screen materials and/r the additin f a secnd thermal screen (whether mveable r temprary). We believe that there is the ptential t save a further 20-40kWh/m 2. This wuld bring the ttal annual energy use f a mdern, but far frm state f the art greenhuse, dwn t the same levels as thse being achieved at the Imprvement Centre (NL) using the New way f Grwing. As with many energy saving technlgies and/r alternative heat surces, the need fr CO 2 in edible crps in particular limits the savings they can deliver fr as lng as grwers are reliant n natural gas as their surce f CO 2. Greenhuse climate The greatest cncern abut the dehumidifiers used fr the trial was their heat distributin characteristic. Warm air discharge was delivered ver the tp f the crp cntrasting with Agriculture and Hrticulture Develpment Bard All rights reserved 40

41 warm air rising frm heating pipes with a cnventinal ht water system. One impact f this culd have been slwer ripening f the fruit, but this was nt evident in the crp data. One thery was that the warm air being blwn acrss the tp f the crp cntributed t the vegetative shift f the crp arund week 11. Hwever, the crp advisr did nt believe that this was the case. A secnd cncern was whether fur pint surces f heat, albeit with built-in fans t deliver increased air mvement, wuld deliver gd temperature unifrmity. A netwrk f data lggers shwed that, if anything, there was a slight imprvement in temperature unifrmity when the dehumidifiers were used. Crp Althugh there was a negative impact n yield, the nursery s crp advisr is cnfident that it can be avided in the future. This des hwever remain t be prven and will be tested in the fllw up HDC funded prject PE 013a. The mst psitive finding in relatin t the crp was that n fungicides were applied t the crp with dehumidifiers whereas the cntrl crp had tw applicatins. Nte these results are frm ne year f trials and there were n replicates. Ornamental crp mdelling The need fr less dehumidifiers per Hectare reduced the capital cst cmpared t an edible crp. Cmbined with the fact that they can be perated all year (nt restricted due t the need fr CO 2 ) the end result financially is reasnably attractive. Lwer energy use rnamental nurseries that use gas il fr heating have less t save in energy (kwh) terms. Hwever, the substantially higher unit cst f gas il means that dehumidifiers culd still represent a gd investment. Dehumidifier perfrmance with lwer temperature crps (less than 16 C) will be less than detailed abve. The effect f this culd nt be quantified. Agriculture and Hrticulture Develpment Bard All rights reserved 41

42 Cnclusins Edible crp trial Heat savings f 91kWh/m 2 p.a. (24%) were achieved. Nte this excluded 1 mnth f ptential savings Dehumidifier electricity use f 19kWh/m 2 N fungicides were applied t the dehumidifier crp cmpared with tw applicatins t the cntrl crp Yield in the dehumidifier crp was 1kg/m 2 less Advice suggests that this can be avided in the future Return n investment 9 years based n current perfrmance (excluding yield lss) Reduces t 6 years if experience gained frm 2013 trials is prven in 2014 The need fr CO 2 (frm burning natural gas) during the summer significantly limits the savings that are pssible. Ornamental crp mdelling Savings f 97kWh/m 2 (37%) were calculated vs. electricity use f 19.5kWh/m 2 The need fr less dehumidifiers means that a return n investment within 4 years appears pssible. Nurseries that use gas il fr heating tend t be lwer energy users. Hwever, the high cst f gas il ffsets the lwer kwh saving and culd deliver a return n investment within 3 years. Knwledge and Technlgy Transfer Tmat Wrking Party nursery visit, April 2013 HDC Energy News July 2013 Tmat Grwers Assciatin Technical Cmmittee meeting, September 2013 Tmat Grwers Assciatin Annual Cnference, September 2013 British Prtected Ornamentals Assciatin Technical Cmmittee meeting, Octber 2013 Agriculture and Hrticulture Develpment Bard All rights reserved 42