Predictive Pre-cooling Control For Low Lift Radiant cooling USING BUILDING THERMAL MASS. Motivation : energy and climate. Addressing energy, climate and development challenges Buildings use 40 % of energy and 70% of electricity 1
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Predictive Pre-cooling Control For Low Lift Radiant cooling USING BUILDING THERMAL MASS
Addressing energy, climate and development challenges
USDOE 2006. Building Energy Databook
IPCC 2007. Fourth Assessment Report
Sivak 2009. Energy Policy 37
McNeil and Letschert 2007. ECEEE 2007 Summer Study
Predictive pre-cooling control for low lift radiant cooling using building thermal mass can lead to significant sensible cooling energy savings.
Cooling strategy that lever-ages existing technologies:
…to save cooling energy:
Simulated energy savings: 12 building types in 16 cities relative to a DOE benchmark HVAC system
Total annual cooling energy savings
(Katipamula et al 2010, PNNL-19114)
Simulated total annual cooling energy savings:
28 % annual cooling energy savings
(Katipamula et al 2010, PNNL-19114)
700 psia
Low lift vapor compression cycle requires less work
600
500
400
300
Vapor compression cycles shown under typical and low-lift conditions
60
Low-lift refers to a lower temperature difference between evaporation and condensation
200
Predictive pre-cooling of thermal storage and variable speed fans
40
T - Temperature (°C)
Variable-speed compressor adapts exactly and efficiently to conditions
20
100
Radiant cooling and variable speed pump
0
1
1.2
1.4
1.6
1.8
S - Entropy (kJ/kg-K)
LLCS operates achiller at low lift more of the time
where COP = f(Tx,Tz,Q) [kWth/kWe],
subject to just satisfying the daily load requirement:
Predictive pre-cooling control requires a chiller model to predict chiller power consumption, cooling capacity and COP at low-lift
To identify a chiller model under low lift conditions:
Low lift operation
COP ~ 5-10
Typical operation
COP ~ 3.5
EER
51
34
17
4-variable cubic polynomial models
LLCS control requires zone temperature response models to predict temperatures and chiller performance
OPT = operative temperature
OAT = outdoor air temperature
AAT = adjacent zone air temperature
QI=heat rate from internal loads
QC = cooling rate from mechanical system
a,b,c,d,e = weights for time series of each variable
Temperature sensors: OPT, OAT, AAT, UST, RWT
Power to internal loads: QI
Radiant concrete floor cooling rate:QC
Models validated based on accuracy of predicting different data 24-hours-ahead
Sample validation temperature data
Sample validation
thermal load data
Transfer function models accurately predict zone temperatures 24-hours-ahead
Operative temperature (OPT)
Under-slab temperature (UST)
Return water temperature (RWT)
Root mean square error (RMSE)
for 24 hour ahead prediction of validation data
OPT RMSE = 0.08 K
UST RMSE = 0.15 K
RWT RMSE = 0.84 K
Perform optimization at every hour with current building data and new forecasts
Pattern search initial guess at current hour
24-hour-ahead forecasts of outdoor air temperature, adjacent zone temperature, and internal loads (OAT, AAT, QI)
Pattern search algorithm determines optimal compressor speed schedule for the next 24 hours
Operate chiller for one hour at optimal state
Pre-cooling the concrete floor maintains comfort and reduces energy consumption
Pre-cooling the concrete floor maintains comfort and reduces energy consumption
Prior research shows dramatic savings from LLCS, but
How real are these savings?
What practical technical obstacles exist?
FROM RADIANT FLOOR
CONDENSER
FROM INDOOR UNIT (CLOSED)
BPHX
TO INDOOR UNIT (CLOSED)
COMPRESSOR
TO RADIANT FLOOR
ELECTRONIC EXPANSION VALVE
TEST CHAMBER
CLIMATE CHAMBER
LLCS and SSAC use the same outdoor unit
IDENTICAL FOR LLCS AND BASE CASE SSAC
LLCS provides chilled water to a radiant concrete floor (thermal energy storage)
17’
EXPANSION TANK
FILTER
TO CHILLER
RADIANT FLOOR
12’
BPHX
RADIANT MANIFOLD
FROM CHILLER
WATER PUMP
TEST CHAMBER
CLIMATE CHAMBER
Chiller/heat pump
Radiant concrete floor
Tested LLCS for a typical summer week in Atlanta subject to standard internal loads
Atlanta typical summer week and standard efficiency loads
Based on typical meteorological year weather data
Assuming two occupants and ASHRAE 90.1 2004 loads
Run LLCS for one week *(after a stabilization period)
Run split-system air conditioner (SSAC) for one week*
Compare sensible cooling only
Mixing fan treated as an internal load
Repeat for Phoenix typical summer week, high efficiency loads – to be completed after climate chamber HVAC repairs
Outdoor climate conditions
Internal loads
Atlanta test
Phoenix test
LLCS ENERGY SAVINGS relative to SSAC in Atlanta subject to standard loads
Similar to simulated total annual cooling energy savings, 28 percent, by (Katipamula et al 2010)
Predictive pre-cooling control can be applied to other systems to achieve low lift
Masdar Test Building
Slab Temperatures
Freshly Poured
Test Building Instrumentation
Masdar City Phase 1b Demo
Refine LLCS methods
Concrete-core and radiant systems gaining market share, and familiarity among architects and engineers (primarily in Europe)
Automation systems are becoming more prevalent/sophisticated
Capital cost savings for LLCS in medium office buildings,
-0.58 $/sqft incremental cost relative to $7.91/sqft base cost1
Adapt components of LLCS to existing buildings and different new and existing building types, e.g.
1. Katipamula et al 2010, PNNL-19114