VCWA202 Controls Providing Flexibility

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Controls providing exibility for the customerincrease comfort and save energyHalldor Kristjansson, Danfoss A/SPublished in HOT| COOL I/2008, DBDH (www.dbdh.dk)

Technical paper

MAKING MODERN LIVING POSSIBLE


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2 Danfoss District Energy

One of the main advantages of thedistrict heating system is its excellentexibility in utilising waste heat andCHP, as well as most kinds of primaryenergy sources. It is relatively easy to

replace one fuel type with a new one,in case of fuel shortage, or for thepurpose of reduction of fuel costs andenvironmental straining.Another kind of exibility is involvedwith the consumer end of the DHsystem. The heat supplied from the DHsystem to the consumer should matchthe heat demand of the individualconsumer as much as possible. Anydifference between the consumer heatdemand and the heat supplied makesup an energy-saving potential. Theenergy savings can be obtained bymeans of local control equipment(temperature and balancing controls).In theory, it may be possible to designa constant ow heating system withperfect radiator dimensions in a blockof ats. In reality, it is not possible toavoid overheating without localautomatic controls, for the followingreasons: the ows can not be balanced;the dh temperatures are not precise;the insulation effect of a room differfrom preconditions; the wind one dayis from the south and the nex t dayfrom the north; the heat balance is

inuenced by elec trical installationsand persons in the room; the residentsdiffer in their preferences about indoortemperature (Fig. 1), etc. For instance,elderly people and parents to babies

may choose higher indoortemperatures, whereas lowertemperatures are preferred inbedrooms.

In case of heating systems withoutlocal controls, it is necessary tooverheat one part of the building toensure that all residents in anotherpart of the building get sufficient heat.

This results in huge energy lossesrelated to high indoor temperatures,the so called open window losses

Author(s)

Halldor Kristjansson ,Application Consultant, Danfoss A/SDanfoss District Heating, Nordborg, Denmark,+45 7488 2962 [email protected]

Increasing energy prices, together with more demands for comfortlead to further development of DH consumerend technologies. This development involves better controlling and metering possibilitiesfor the individual consumer, so unnecessary heat supplied to theconsumer is not wasted. Maximum individualisation of the heat supplyis becoming more feasible than ever. In the case of blocks of ats, this

brings about thermostatic radiator valves and a district heating unit forthe individual ats, the at station. And blocks of ats include a hugeenergy-saving potential, as they traditionally make up a big part of theDH consumers in most cities. In the former Eastern bloc countries, theyconstitute the majority of consumers.

FIGURE 1: In theory, it may be possible to adjust the heat supply to the heatdemand without local controls but not in reality. The gure showsthe room heat supply, but the same principle applies to the hottap water supply.

TECHNICAL PAPERControls providing flexibility

for the customer increasecomfort and save energy

Individual demand and xed supply in a block of ats

Various demand preferences by residents (example)

Actual supply without local controls (example)

Indoor temperaturescalehot

20C

cold


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3Danfoss District Energy

(Fig. 2). This design was chosen inmany Eastern regions in times with lowfuel prices. In later periods ofrecession, the heat supply was limited,leaving some of the residents with verycold rooms. In this case, an evendispersion of the scarce heat wouldhave improved the average comfortlevel considerably.Comfort level is an important factorinvolved with energy consumption.Economic growth results in increaseddemands of comfort, which in case ofnon-controlled systems leads toa rapidly increasing heat consumption(Fig. 3). The saving potential of local automatic

controls would be underestimated,if the rst sight savings were notadjusted according to thedevelopment (left side of Fig. 3). Thecorrect reference basis is what the heatconsumption of the obsolete systemwould have been in the future. Theseconditions, together with increasingenergy prices, can make investment inlocal automatic controls far morefeasible than at rst sight. The most common examples ofincreasing comfort demands are the

available higher indoor temperatures,elongated heating seasons, more airventilation, and a stable suitable hottap water temperature. The literatureincludes extensive formulas for, forinstance, how indoor comfort dependson indoor air temperature, draught,radiation, humidity, air dust andchemical composition. The purpose of automatic controlequipment is to t the heat supply tothe individual consumer demands,with a minimum of losses. It isimportant to distinguish betweendifferent levels of individualisation ofthe control (Fig. 4). The traditionalEastern regional designs are found inthe left side of the gure, while thebest control quality is found in theright side of the gure. This design involves thermostaticvalves on all radiators and a substationwith a heat meter for every at, the socalled Flat Stations. This design allowseach family to optimise the indoorcomfort and hot tap water preparationwith the heat cost from time to time,providing maximum energy savings(Fig. 5).

FIGURE 2: Individual needs for heat should be met with individual controls.Otherwise, either comfort, heat, or both, are lost. Note that several parameter alternatives exist on both axes.

FIGURE 3: Within unregulated systems, economic growth results in a substantialincrease in heat consumption and an increased saving potentialthrough local automatic controls. The leftmost side of the gureindicates a tempting underestimation of the nal savings potential.

The demand - Supply difference is an energy saving potential - but comfort is involved

Parameters involvedwith heat consumption: - heat demand, - room temperature, - hot tap water temperature, - htw. circulation temperature, etc.

Parameters involved withindividual situation: - room number, - house, - at, - individual (person), - hour of day, - lenght of heat season preferred - shower and tapping equipment - energy price - family economy, etc.

1 2 3 4 5

Heat supply,surplus

Heat losses(cost)

Heat supply,shortage

Comfortlosses (cost)

Heat supply,local controls

Heat savings

Example:Net heatdemand

Increase in saving potential caused by growth

Annualenergy

consumption

Saving potential of

controls

Final Simple

year 0 later time [years]

Heating system withoutany automatic controlsinside building

Economicalgrowth increasesenergy demand

Heating system withlocal automatic controls

Good times withopen window regulation

25C

Hard times

25C a

b

c

Technical Paper Controls providing flexibility


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Evaluation of the energy-savingpotential of local automatic controlsonly becomes credible when alsoconsidering the comfort level. Energysaving data have to be cleaned fordifferences in comfort level. If thecomfort level were not considered, themost efficient energy savings would beobtained by simply turning off theheat! No controls needed! But as far asthe future brings increasing demandsfor comfort as well as energy savings,a maximum individualisation ofcontrols is the most relevant issue.Another important effect of the atstation design is that the authoritiesrelatively quickly can obtain optimalenergy savings by raising the energyprice during energy crises. It should bekept in mind that building distributionsystems are normally constructed forthe purpose of lasting several decades,while energy crises can occur withinunexpectedly. This is especiallyrelevant for many european countrieswhich rely on imported primaryenergy. The third important effect of the atstation system design is thatinstallations are maintained, as their

condition inuence the consumers billdirectly. Experience shows that jointlyowned substations hidden in cellarsare poorly maintained, causingunnecessary losses and too highreturn temperature in the DH pipenetwork.As for the riser pipe system, thebasement is lled with hot tap waterand room heating pipes connected toseveral riser pipe pairs drilled upthrough the oor and ceilings of ats(Fig. 6). According to the literature, the

HTW system heat losses are biggerthan the net heat for preparing theHTW.As for the at station system, thebasement only includes DH pipesconnected to one DH riser pipe pairin each staircase.All HTW and room heating pipes areplaced inside the ats, usually behindnice-looking skirting boards.(Hydraulic separation and/or a mainheat meter in the basement is still anoption, if required).As for the riser pipe system, the HTWand circulation pipes are kept hot all

FIGURE 4: There are several levels of individualisation of control equipment.They heavily inuence both the energy consumption and thecomfort level.

the time, causing considerable pipeheat losses, and, by the way, the risk ofhygienic problems may be increased(Fig. 7). Only 20 30 % of the HTW andcirculation pipe heat losses is utilisedfor room heating, the rest are nallosses.As for at station systems, the HTWpipes are mostly idle, and mostfamilies would not utilise a circulationpipe, or only shortly according toa timer function. Even if the totallength of pipes is slightly larger in caseof at station systems, the heat lossesare lower due to operation time of thedifferent parts of the system (Fig. 8).And as for investment, it is more

convenient to lay horizontal pipesinside ats than to drill riser pipesthrough concrete oors. The piping makes it possible to makeindividual adjustments of the roomheating season. A resident on the topoor would typically prefer the longestheating season. In riser pipe systems,this would keep all risers hot for anextra 500 hours. In case of at stationsystems, this makes no difference. Anexample of energy savings related toindividualisaton and comfort demand.According to measurements of a few

groups of houses in Denmark between1991 and 2005, individual billingresulted in savings of 15 30 %. Savings

Individualisation of controls in blocks of atsFew alternatives in basic designs

1 2 3 4 65

1 2 3

R

N

N

N

N

N

N

R

N

N

N

N

N

R

R

R

R

R

R

R

R

RR

R

Basic control level 1 better 2 better 3 better 4

better 5

best 6.

Basic control level Better Best

R

R

R

R

R

R

R

R

R

R

Room heat part

Hot tap water part

SubstationBuilding block Flat station ( HTW HEX, heat meter, etc.)

DH pipe (f. & return)HTW pipe (& circ)

N : No automatic controlsR: Automatic controls, room heat R: Automatic controls, HTW

N

N

N

N

N



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5Danfoss District Energy

of 15 %, out of an energy cost ofEUR 1,000 per year, would generateEUR 1,500 for the consumer over thenext ten years, provided that energyprices are xed. But energy prices willprobably not stay constant for long - asit is with the demand for comfort inmany countries. The at station design principle is animportant opportunity for energysaving activities in the near future.

FIGURE 6: Principal geometrics and operation modes in case of two basic designs of heat supply system.

FIGURE 5: The increasing demand for both comfort and energy savings urge theindividualisation of automatic controls. The most reliable energysavings are achieved in a system where the individual consumer isallowed to optimise comfort and energy cost (system D).

Energy consumptioninuenced by comfort level and control individualisation level

Energy consumption(annual cost for consumer)

Authority - or consumer

demand for energy savings

Consumer demand for better comfort Comfort level

(average, revenue for customer)

I n d i v i d

u a l i s

a t i o

n -

l e v e l o

f c o n t r o

l s

15 C

25 C

A. Heating system without any automatic controlsinside building

B. Automatic controlsin block basement

C . + thermostatic valves on radiators

D. + + at stationwith hot water preparation, energy meter, individual billing

Open window -regulation

Hard times

A B C D

13

5

(2)

(4)

Piping of two basic designs in a block of flats

Riser pipe system Flat station system

(If required)

Station

Heat meter

Sink, shower, etc.

Radiator HTW / circ CW

DH or RH Hot all day (winter only)Hot few hours / day (all year)

Hot all day (all year)



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FIGURE 8: Comparison of pipe lengths and pipe heat losses for a riser pipe system and a at station system. Operation time indifferent parts of the system strongly inuence the nal heat losses. The example concerns a four-storey buildingwith ats of 120 m 2 each.

FIGURE 7: The Flat Station System decreases the risk of hygiene problems in the hottap water, as it is prepared immediately before consumption,in a one-way ow. In riser systems, the water may ow in a loop fordays, through or past pipes with inexpedient temperatures.

Hygiene risk from basic design of hot tap water system

Riser pipe system Flat station system

Hot tapwater 55 C

Cold water 10 C

Fresh hot tap water 50 C

Cold water

Riser pipes

??C

HTW circulation

Pipe lenght (m / at)

Gross pipe losses(w.av. / at)

Net pipe losses (nal)(kWh /y / at)

HTWater living

HTWater basem

RmHeat living

RmHeat basem

DH living

DH basemRiser pipe

system

Flat stationsystem

Riser pipe

system

Flat stationsystem

Riser pipe

system

Flat stationsystem



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VF.CW.A2.02 Produced by Danfoss A/S, DH-SM/PL 09/2011

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VCWA202 Controls Providing Flexibility