Literature Review: Small-Scale Heat Pumps

Background[edit | edit source]

Heat pumps can be used as an alternative heating and cooling system to reduce the amount of fossil fuel used to preform similar tasks. The purpose of this page is to investigate the feasibility and current and future applications of smaller scale heat pump systems.

Design and fabrication of meso-scale variable capacitance motor for miniature heat pumps[edit | edit source]

R. Agrawal, Q. Hasan, N. Ashraf, , “Design and Fabrication of Meso-Scale Variable Capacitance Motor for Miniature Heat Pumps.”, Journal of Micromechanics and Microengineering, 13(1), 2002

mini motor for refrigeration
using VCM (variable capacitance motor) that is silicon-based
fabrication used pancake method - design of many masks (18.18 mm x 18.104)
4 masks used for rotor and stator
- stator pad connection-bar
- stator dielectric layer
- stator pad
- rotor pads
- carbon layer
possible design for a small system

Design, fabrication, and experimental demonstration of a microscale monolithic modular absorption heat pump[edit | edit source]

Matthew D. Determan, Srinivas Garimella, "Design, fabrication, and experimental demonstration of a microscale monolithic modular absorption heat pump", Applied Thermal engineering, 47, 119-125, 2012

micro absorb HP
fabrication and testing documented
- dims: (200 x 200 x 34 mm), 7 kg
- HX/MX made up of stacks of thin metal
- whole stack made of plates with etched components (40 total, 20 each):
  - SHIM A: condenser, refrigerant HX, Evaporator, Absorber, rectifier, Desorber, Solution HX
  - SHIM B: similar set-up
descriptions of previous attempts at portable cooling systems
feasibility over performance (136-300 W cooling for 500-800 W heat input)

Design, experimental investigation and multi-objective optimization of a small-scale radial compressor for heat pump applications[edit | edit source]

J. Schiffmann, D.Favrat, "Design, experimental investigation and multi-objective optimization of a small-scale radial compressor for heat pump applications", Energy, Vol 35(1), 436-450, 2010

investigation (review and design) into reasons for differences in efficiency between big and small turbo machinery
radial turbo compressor
Limiting factors identified:
- reynolds number, surface roughness
  - increases with smaller impellers
- Tip clearance
  - impaired if its large, avoided with suitable bearings
- feature size
  - issues with scaling and manufacturing process
- non-adiabatic effect
  - important for systems with hot sources close together
  - or high heat exhaust
testrig used to determine if model and design work
- compressor unit, expansion valve, HX, separator in main cycle
- 2nd cycle for refrigerant, for bearing section
results indicate one impeller may be insufficient for an HP
mild climates: A12 design
colder climates: A-12 design

Long-Term Performance Measurement and Analysis of a Small-Scale Ground Source Heat Pump System[edit | edit source]

Hao Liu, Hongyi Zhang, and Saqib Javed, "Long-Term Performance Measurement and Analysis of a Small-Scale Ground Source Heat Pump System", Energies, Vol 13(17), 4527, 2020

outlines system boundary schemes used for evaluating HP system
- gives performance factors
experiment done in a clubhouse building in Sweden (measurements for three years)
- GSHP used for water and air heating in building
- water system portion less efficient than space heating
- 240 m^2 footprint area
set-up:
- 5-kW compressor
- 6-kW auxiliary heater
- 2x circulation pump
- connected to 2x buffer tanks (500-L)
- ground heat exchanger, u-pipe with ethanol/water, 230 m depth in ground
details:
- high hot water demand
- auxiliary heater (3-kW) in hot water tank, legionella protection
consumption (electrical):
- 9.3-10.5 MWh / year total
- compressor: 4.9-5.7 MWh/year
- aux heater: 2.1-2.6 MWh/year
- pumps: 1.2-1.4 MWh/year
- heat pump aux heater: <1 MWh/year except 2014 (1.6MWh)

Design, fabrication and experimental study of a solar photovoltaic/loop-heat-pipe based heat pump system[edit | edit source]

Xingxing Zhang, Xudong Zhao, Jingchun Shen, Xi Hu, Xuezhi Liu, and Jihuan Xu, "Design, fabrication and experimental study of a solar photovoltaic/loop-heat-pipe based heat pump system", Solar Energy, 97,551-568, 2013

description of fabrication
cooling PV & using heat to heat tap water
- COPth = 5.51
- COPpv/t = 8.71
- heat gain for water is avg. 146.86 W (over test duration) (501.107 BTU/hr)
heat-pipe (LHP), spacecraft, lighting applications w/ added heat pump
- vapour-liquid separation (closed-loop)
- includes:
  - evaporator
  - vapor/liquid lines
  - flat-plate HX
  - copper mesh-screen used to minimize radial heat transfer
  - working fluid: 95%/5% water and glycol mixture
  - boiling creating vacuum, exhaust far from boiling

Characterization of a solar photovoltaic/loop-heat-pipe heat pump water heating system[edit | edit source]

Xingxing Zhang, Xudong Zhao, Jihuan Xu, and Xiaotong Yu, "Characterization of a solar photovoltaic/loop-heat-pipe heat pump water heating system", Applied Energy, 102,1229-1245, 2013

system review
- electrical efficiency: 10%
- thermal efficiency: 40%
- overall efficiency: 50%
heat pipe based system
- efficient for heat transfer
- seal prevents leakage
- heat distribution even
- 2-phase, looped
components
- evaporator unit integrated into the PV plates
- flat-plate HX
- PV solar collector
- control/storage (electricity)
- hot water tank (100L)
- compressor
- condenser in tank (coil)
- working fluid (95%/5% glycol and water)
- controller (12V)
- DC/AC converter (500 W)
- battery (12 V)
- insulation materials (polyurethane foam)
comparison of theoretical(computer) and experimental model for sys
- experimental model tested inside in controlled conditions (for a month, from 9am until s-s reached)
also have 1kW heat pump w/ refrigerant (R134a) (3412.142 BTU/hr)
- 85% of electricity used for operation
suggestions for optimization included
- 2 LHP under PV
- 5-10 degrees C evaporation temp

Carbon dioxide heat pipe in conjunction with a ground source heat pump (GSHP)[edit | edit source]

Karl Ochsner, "Carbon dioxide heat pipe in conjunction with a ground source heat pump (GSHP)", Applied Thermal Engineering, vol(28) 16, 2077-2082, 2008

VGSHP
- using CO2 and ground to transfer heat to R407c
sub critical intake, trans critical-supercritical output
- use of CO2 inside tube
  - diffuses through polyethylene
- heat pipe is 2-phase, corrugated steel pipe
  - description of design considerations: 1 pipe or multiple
  - need sufficient diameter to prevent premature evap. (40 mm in example)
  - length = 100 m
- HP system used R407c
  - helical tube HX
installation account in Northern Austria
- heating load = 33 W/m^2, 160 m^2 (18,016.107 BTU/hr)
- for space heating
- weights fixed to in-ground pipe

An experimental study of an ejector cycle refrigeration machine operating on R113[edit | edit source]

Nehad Al-Khalidy, "An experimental study of an ejector cycle refrigeration machine operating on R113", International Journal of Refrigeration, vol(21) 8, 617-625, 1998

ejector cycle tested
- influence of temperature evaluated:
  - boiler, boiled with oil through coil,(can operate >70C)
  - condenser (can operate <45C)
  - evaporator , shell and tube, flooded
- R113 used
  - outlined the criteria for selection, ideally high molecular weight
- fiberglass insulation
- other components: expansion valve
- heat to boil from a solar concentrator collector
- 2-sub systems for calculation
  - power: boiler-ejector-condenser-liquid pump
  - refrigeration: evaporator-ejector-condenser-expansion valve
- Controls for:
  - pressure of boiler
  - refrigerant flowrate
  - oil flowrate(solar system)
  - water flowrate (evaporator/condenser and inlet)

Evaluation of the performance of a ground-source heat-pump system with series GHE (ground heat exchanger) in the cold climate region[edit | edit source]

Kadir Bakirci, "Evaluation of the performance of a ground-source heat-pump system with series GHE (ground heat exchanger) in the cold climate region", Energy, Vol(35) 7, 3088-3096, 2010

performance analysis of Vertical GSHP
- heating season for cold climate over a year in Erzurum, Turkey
COP HP: 2.898 (aprox. 3 for coldest months)
sediment type: alluvial structure for 1km, gravel, sand, clay, and volcanic rock
GSHP w/ multiple GX in ground
- components:
  - compressor (hermetic scroll), electrical motor driven
  - water to refrigerant HX
  - evaporator and condenser (water-cooled plate HX)
  - rubber-foam insulated
  - R134a used
    - boreholes 2 x 53 m deep

An investigation of the heat pump performance and ground temperature of a piled foundation heat exchanger system for a residential building[edit | edit source]

Christopher J. Wood, Hao Liu, and Saffa B. Riffat, "An investigation of the heat pump performance and ground temperature of a piled foundation heat exchanger system for a residential building", Energy, Vol(35) 12, 4932-4940,2010

components:
- 21 x 10 m with single U-pipes
- test area of 72m^2, pile layout, not a building there
- 21 x pile: diameter = 300 mm, depth = 10 m
- polyethylene U tube: diameter outer = 32 mm, thickness = 2.9 mm
- hydronic system
  - buffer tank (180 L)
loading modeled as 27 W/m^2 (coldest conditions), area = 72 m^2 (6,633.2 BTU/hr)
- adjusted monthly from 6 yr data of area
- load taken instantaneous over 24 hrs
transfer of HP heat through plate HX
- heating water (than transferred to air)
- aluminum finned radiator w/ forced convection
testing with thermocouples down piles and in an array

A performance comparison between an air-source and a ground-source reversible heat pump[edit | edit source]

C. A. De Swardt and J. P. Meyer, "A performance comparison between an air-source and a ground-source reversible heat pump", International Journal of Energy Research, Vol(25) 10, 899-910, 2001

ASHP v. GSHP
- GS using municipal water for source/sink
- comparison of heat/cool mode
modeled with HPSIM, predicts behaviour
- inside conditions: 22C, Humidity = 60% (air source)
air source: floor-mounted split
- factory-made HP
- R22 used
- compressor (reciprocating, hermetically-sealed), capacity of 13.7 kW (46,746.34 BTU/hr)
- operating for 5 years prior (Pretoria, South Africa)
- 2 x HX, four circuits, fins and tubes, crossflow
- performance impacted by wet bulb (based on simulation)
ground source: similar inside set-up as air source
- tube-in-tube HX, fluted tube
- capacity of 10.6 kW (36,168.7 BTU/hr)
- municipal water in inner tube, counterflow
- deeper water, better performance
system pays back in 2 years (0.058 $/kWh)

Build-up and long-term performance test of a full-scale solar-assisted heat pump system for residential heating in Nordic climatic conditions[edit | edit source]

B. Stojanovic ́and J. Akander, "Build-up and long-term performance test of a full-scale solar-assisted heat pump system for residential heating in Nordic climatic conditions", Applied Thermal Engineering, Vol(30) 2, 188-195, 2010

testing at house (Sandviken, Sweden)
- poor insulation
- limited radiators
- roof east/west
- 20C inside temperature maintained, no internal heat sources used
- simulated consumption of 2000kWh for summer
- DHW drained 2x/day
- operated and monitored February 2006 to 2088
  - issues in 2007 with fluid in USC system
GHE configuration did not work in its presented design
- when ground below 0, influence of moisture noticeable
- system requires recharging
solar system with a GSHP
- charges ground during non winter months/ evaporator temperatures raised
- domestic water heating included with space heating (radiator circuit)
- components:
  - 39 endopanels (forms large flat panel across whole roof)
  - IVT Greenline HT Plus 9C (8.4 kW)
    - built-n DHW tank, auxiliary heat (electric)
  - GHE (storage), horizontal at 1.5 m, area of 52 m^2
  - control equipment, valves, CPs

Changes in the thermal performance of horizontal boreholes with time[edit | edit source]

Richard A. Beier and William A. Holloway, "Changes in the thermal performance of horizontal boreholes with time", Applied Thermal Engineering, Vol(78), 1-8, 2015

sample of 10 boreholes
- ground thermal conductivity
- borehole resistance
- depths from 1.9-3.4
- adverse effects observed in shallow holes
clay soil, Stillwater, Oklahoma
polyethylene U-pipe (3/4 diameter,SDR-11)
- 6 with benotonite grout (23% solids)
- 8 drilled with benotonite based fluid, 2 with polymer-based fluid
- included a horizontal and angled section
tested from June 17-Aug 8 2010 (round 1)
tested from October 16 - November 4, 2012 (round 2)
- stagnant between tests
drought over testing period (affected thermal performance of boreholes)
results
- shallow holes (less than 2.4): 1.2-2.0(W/m.K)
- Deep holes (2.9 and 3.4 m): 2.8-2.6 W/(m.K)
- no differences for grout and non-grout and drilling

Performance of multi-functional domestic heat-pump system[edit | edit source]

Jie Ji, Gang Pei, Tin-tai Chow, Wei He, Aifeng Zhang, Jun Dong, and Hua Yi, "Performance of multi-functional domestic heat-pump system", Applied Energy, Vol(80) 3, 307-326, 2005

multi-functional domestic heat pump (MDHP)
- cools while producing hot water
components:
- air-cooled condenser
- water-bath condenser
- 3x valves
- evaporator
- four-way valve
- compressor
- 2x capillary tubes (w/ throttling equipment)
- R22 used
3 modes:
- water-heating
- water-heating + space-cooling
- space-heating
tested with in a two-room controlled environment (insulated)
outlines equations of component models
- found to be robust

Experimental thermal performance evaluation of a horizontal ground-source heat pump system[edit | edit source]

Mustafa Inallı and Hikmet Esen, "Experimental thermal performance evaluation of a horizontal ground-source heat pump system", Applied Thermal Engineering, Vol (24) 14, 2219-2232, 2004

HGSHP
- location (38.41 N, 39.14 E, Turkey)
Components (3 circuits):
- working fluid: R22
- 25% glycol water solution to prevent pipes freezing (antifreeze)
- Ground coupling:
  - 2x HGHX
  - antifreeze pump (Alarko,NPVO-26-P)
- Refrigerant:
  - HX (air-cooled condenser)
  - HX (brine and R22)
  - capillary tube (copper)
  - compressor (Tecumseh Europe, hermetic)
  - dryer (Carly DCY 083)
  - observe glass (Carly VCYL 13)
- Fan :
  - condenser fan (Friterm)
tested in a room (16.24 m^2) with a window
- Ground HXs at 1-2 m
- 6 month testing period
- at 20C inside room
results:
- COPsys: 2.66 and 2.81
- properties of soil should be taken before design to prolong life span

Experimental study of a closed loop vertical ground source heat pump system[edit | edit source]

Arif Hepbasli, Ozay Akdemir, and Ebru Hancioglu, "Experimental study of a closed loop vertical ground source heat pump system", Energy Conversion and Management, Vol(44) 4, 527-548, 2003

testing of a water-water GSHP
- location: classroom in Izmir, Turkey (38.24 N,27.50 E) (65 m^2)
- heat/cool loads (3.8/4.2 kW)
- thermal diffusivity of soil (avg. 0.00375 m^2/h for avg. 2 m)
- soil had clay, sand, and silt
components
- working fluid : R22 in refrigerant cycle
- 10% ethyl glycol used to prevent freezing
- Ground circuit:
  - 50 m vertical GHE, U-bend
  - brine pump (Marina,KPM 50)
  - Expansion tank (Zimmet, 541/L)
- Refrigerant circuit
  - 2 x HX (Alfa Laval, CB 26-24,CB 26-34)
  - Capillary (copper)
  - Desuperheater (Alfa laval,CB 14-6)
  - Compressor (herematic, Tecumseh, TFH 4524 F)
  - Fan-coil units (Alarko,SAS 28)
  - Expansion tank (Zimmet, 541/L)
- Fan-coil circuit:
  - water circulating pump (Marina, KPM 50)
results:
- COP (carnot HP) = 5.4
- 11 W/m extraction for bore depth
- capacity 3.405 kW heating (11618.34 BTU/hr)
- COP (system overall) = 1.656-1.339 (8 C)
- oversized system components brought down efficiency
- suggest detailed measurements of soil temperature
important design considerations
- size
- depth of boreholes
- capacity of system
- fluid used for heat transfer
- flow rate of fluid
- pipe size
- spacing of GHE
- soil type

Analysis of gyroid heat exchangers for superconducting electric motors[edit | edit source]

Oliver Bonner-Hutton, Bastian Busch, Yifan Lv, Alan Caughley, Rodney Badcock, Grant Lumsden, Hubertus Weijers, and Sarat Singamneni, "Analysis of gyroid heat exchangers for superconducting electric motors", Materials Today: Proceedings, 2023

triply periodic minimal surfaces (TPMS)
- free form surfaces made up of trig functions, repeat in 3 dimensions
- ex. Gyroid sheet-network (in this paper)
- reduces frictional energy loss
- counter-flow design
geometry generated from equations in MATLAB
designed compared to block of tubes
- same dimensions as gyroid block ( 50x50x100 mm)
SLM (selective laser melting)
analysis of overall energy efficiency at varying fluid velocities
results:
- greater heat transfer but also pressure loss
- geometry randomly selected, could be optimized, changed until it meshed with ANSYS fluent