MCS Based Design for GSHPs “Horses for Courses”

MCS Based Design for GSHPs –

“Horses for Courses” GSHPA Energy Expo – Stone – Sept 2017

Robin Curtis – GeoScience Ltd

Dog ‘n Pony Show 

Robin – on “MCS”why / how / what / when / where 

Chris – on “not‐the‐MCS” approachwhy / how /when /where 

Objectives

‐ Background setting‐ Underlying reasoning & approach‐ The MIS‐3005 design “products” ‐ Focus on the ground loop sizing  &‐ Hydraulics                                      

New ground loop sizing toolsfor Domestic GSHP installationsin the UK

Robin Curtis & Tom Pine  ‐ GeoScience Ltd. Chris Wickins ‐ UK Dept. of Energy & Climate Change

EGC – Pisa June 2013

1st UK Closed Loop GSHP Domesticinstallation

1995 Devon   (~8kW)

22 years ‐ 1st routine maintenance/inspection this year. (apart from air‐filter changes)

Background 

The “infamous” EST study

…the intentions………

…the unintended consequences

DECC steps in……. 

Revise guidance for all domesticheating heat pumps (MIS 3005) For all heat pumps (ie ASHPs and GSHPs):

Improve building heat loss estimation

Produce a Heat Pump Emitter Guide 

Require ~ 100% heat pump sizing(for mono‐energetic systems)

Specifically for GSHPs ‐

New guidance for ground loop sizing

Guidance for hydraulic  design

LASHUP ‐ 2Ground related issues

DECC ‐ 9 Mar 2011

“Crazy”paving ?

Ground parameters

ffBuilding thermal loads

Available space Heat pump / SPFFlow rate / min EWT

Total ground loop length+ spacing 

Code ‐ for say, 20 years 

Hydraulics – SPF2? 

Costing 

Heat loss / energy ? 

Energy assessment for closed loop GSHPs–“THE” fundamental 

difference(compared to all fossil fuel boilers, direct electric, and ASHPs ) 

Heat generator

NOT your worry Your worry Your worry

Gas 

LPG 

Oil 

Air 

Conventional – non GSHP heating 

Heat generator

YOUR worry Your worry Your worry

GSHP heating 

Your worryNot dealing with it here ‐

Other than:

1)  FLEQ’s

Annual kWh / heat pump size kW

Ground impact ?

2) Estimated SPF (heat emitter guide)

Ground impact

Ground loop sizing / design

Underlying philosophy

• Conservative• Simple – available to all• Paper based – no HW/SW version issues• Domestic heating + DHW only (<45kW)• To obtain acceptable SPFs• Not the best or cheapest

Previous methods ? Some use of software, eg EED, GLHEPRO, GLD, CLGS

European manufacturers’ software 

VDI 4640 

The well known ROT method 

Concerns ?  Relevance to UK conditions ?

“Ground” rules 

100% sizing – for mono‐energetic systems

Minimum entering water temperature(EWT) O°C(after 20 years) – to maintain SPF

Boreholes Fixed parameters:single 32mm U‐tube, specified borehole resistance, minimum spacing defined

Variable parameters:

Ground equilibrium temperatureThermal conductivityAnnual thermal loads (Run hours / FLEQ) 

for all UK

geology &climate 

Boreholes 

Over a (UK relevant) range of k, ground temperature and FLEQ

Run:      EED, GLHEPRO

Make some check comparisons with VDI 4640 and GLD. 

Ground loop sizing….

Geo En er gy

NB – for domestic sub 45kW ONLY – heating only  

Draft Issue 1.0 (24/08/2011)

5.0

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Mean ground temperature (oC)6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0

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NW

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Mean annual air temperature for UK regions (oC)

14

29

25

20

16

32

28

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18

37

32

26

21

41

35

29

22

45

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Maximum power to be extracted per unit length of borehole heat exchanger (W/m) with 3600 FLEQ run hours

Conditions for use:Heat extraction only (inc. hot water)

6m minimum borehole spacing. Only valid for boreholes arranged in a line; not applicable for a large number of systems in a small areaTable created assuming: 130mm borehole diameter; single U-tube; 32mm OD SDR-11, PE100 pipe with thermal conductivity = 0.420W/m/K; 52mm pipe centre-pipe centre

shank spacing; 25% Mono Ethylene Gylcol thermal transfer fluid; Re > 2500 in the borehole active elements; thermally enhanced grout with thermal conductivity = 2.4W/m/KAssumptions result in borehole thermal resistance = 0.1 m.K/W at 12oC mean ground temp. and 2.5W/m/K average ground thermal conductivity

Horizontal systems Conventional EU style loops (Serpentine) , and SlinkiesFixed parameters: Geometrical layouts and pipe sizes defined.

Variable parameters:Ground equilibrium temperatureThermal conductivityAnnual thermal loads (Run hours / FLEQ)+ Temperature “swing” and depth 

from Tufte

Horizontal systems Over a (UK relevant) range of :k, ground temperature and FLEQ

Run:     CLGS

Make some check comparisonswith VDI 4640 and GLD. 

Ground loop sizing….NB – for domestic sub 45kW ONLY – heating only  

Hydraulics designof closed loop GSHPs 

The challenge !!

An oversized circulation pump consumes electricity!Ruins performance!

Hydraulics ‐Pressure dropcomponents:

1) Active element(s)2) Headers3) Heat pump4) + contingency/fittings

Hydraulics ‐fixed parameters

• Heat pump flow rate • Non‐laminar – (transition zone)• min % Anti‐freeze

Hydraulics ‐the variables 

• Borehole/loop lengths vs number• Pipe diameter • Borehole pipe configuration (1U / 2U)• Header arrangements

Flow Rate (l/s)

P r e s s u r e D r o p ( k P a / m o f P i p e )

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

00.1

0.20.3

0.40.5

0.60.7

0.80.9

11.1

1.21.3

1.41.5

1.61.7

1.81.9

22.1

2.22.3

2.42.5

2.62.7

2.82.9

33.1

3.23.3

3.43.5

3.63.7

3.83.9

4

SDR11 Header Pipework -Ethylene Glycol (-10°C)

System curve + pump curve

0

5

10

15

20

25

30

35

0 2 4 6 8 10 12Flow rate

Pre

ssu

re d

rop

or

Hea

d

System curvePump curve

The deliverables:

1) flow charts 

2) pressure drop charts

3) accompanying design guide

for:   2 pipe types2 antifreezes2 freeze protection limits@ various pipe diameters 

Links to all of these resources are given in the paper.

Methodology should be applicable to any other country / region.(?)

Awaiting incoming criticism /comment/exocets > 

>>>>  Revision / update

OUTCOME ?

But – if you want to get more     advanced…...........

listen in..........

• Thank you.

Ground Loop Design& the limits of MIS 3005

The Many Faces of Building Loads

Design Day vs Monthly Loads

Design Day (EqFLH)CoolingkW

HeatingkW

0800‐1200 0 142.0

1200‐1600 0 59.7

1600‐2000 0 59.7

2000‐0800 0 59.7

EqFLH 0 2,896

Monthly LoadsHeat Gains Heat Losses

Month Total kWh Peak kW Total kWh Peak kW

Jan 0 54,628  142

Feb 0 52,137 Mar 0 48,869 Apr 0 40,931 May 0 28,791 Jun 0 19,141 Jul 0 0 13,693 Aug 0 14,160 Sep 0 18,207 Oct 0 29,258 Nov 0 41,242 Dec 0 49,491 

Then the Heat Pumps

kWHR

kWHE

kWe

COP = kWHR / kWe

kWHR ≈ kWHE + kWe

Heat Pump Properties

MIS 3005• Assumes you calculate the COP at the design condition and apply that to the building load

• So it returns Heat of Extraction

• No corrections for flow rates

Design Software• Holds data for,

• Source temperatures• Load temperatures• Source flow corrections• Load flow corrections• Heat Pump limits

• Extrapolates & Interpolates from published data

Ground Conditions

MIS 3005• Inputs,

• Undisturbed Ground Temperature

• Conductivity

• Fixed,• Diffusivity

Design Software• Inputs,

• Undisturbed Ground Temperature

• Conductivity• & Conductivity Averager• Diffusivity• & Diffusivity Averager• TRT Data & Processing

Pipes & Pumps

MIS 3005• Basically all fixed,

• 130mm bores• 32mm pipes• 25% MEG• Limited horizontal options

• Turbulent• 2.4 W/mK grout

Design Software• Inputs,

• Circulation Pump Loads• Fluid Properties• Pipe Diameter• Placement in Bore• Horizontal geometries

• 6 pipe, 4 pipe etc• Grout properties• Flow Conditions

• Laminar ‐ Transition ‐ Turbulent

Borehole Locations

In MIS 3005 World In the Real World

The Effect….

• Block of Apartments• 142 kW, 2,896 EqFLH• MIS 3005

• 24 x 169m• 6m spacing

• Actual Design• 24 x 193m• See layout right• BUT it will work!

The Effect….

Take Away Messages….

• Exceptions to the MIS 3005 tables do exist• Know the limits of look‐up table “design”• Look out for the warning signs• Pipe is cheap!• Keep your spacings up – Borehole & Slinky Pitch• Consider further training• Please, Please, Please ask for help