Tappvattenvärmning med värmepump. Krav och erfarenheter.

• This licentiate thesis deals with system solutions for heat pump hot water heating inSweden. Hot water heating requires higher temperatures than space heating and thereforelowers the annual performance of the heat pump system. In existing single family houses,space heating represents the majority of heat pump delivered energy. The demand forspace heating decreases in new buildings meanwhile the demand for hot water heatingremains, concurrently efficient hot water heating becomes more important.The choice of system solution affects the possibility to save energy. The prerequisites forsystem development in small houses are examined in this work. It is done partly by asummary of today’s heat pump systems, i.e. the heat pump unit and storage tank, basedon different principles for hot water heating. The summary includes pros and cons withthese system solutions. The work is also done partly by a survey of demands,requirements, recommendations and testing methods for hot water that can influence thesystem design. In addition, analysis of data from field measurements on three domesticheat pump systems shows demands, energy relationships and heat pump operation inexisting single family houses.Heat pump hot water heating requires some kind of storing of energy since theinstantaneous power requirement for hot water heating is huge and the heat pump poweris designed for the space heating demand. Typically, tap water is stored in a tank andnatural convection is used for the hot water heating. It is important to maintain thetemperature stratification in order to maximize the energy extraction from the storagetank. Systems depending on natural convection for water heating, risk unwanted mixingwhen tapping or recharging occurs. In order to avoid this, the design of the system isimportant. Storing of water in a closed water loop system decreases the risk of Legionellagrowth and makes it possible to use a simpler and cheaper tank, compared to fresh waterstorage as in conventional systems. Hot water heating in an external heat exchangerlowers the risk of mixing in the tank. The heat exchanger dimensions and power can bechosen more freely since it is not limited by the space in the tank as with internal heatexchange.Few measurements on tap water usage are available from single family houses whilemany exist for multifamily buildings. Standard estimate energy usage for hot waterheating is typically between 4000-5000 kWh/year in single family houses. The resultsfrom a questionnaire survey made for single family houses with new heat pumpinstallations, shows that the users are well satisfied with the amount and temperature ofhot water.Testing methods for hot water heaters tend to move towards detailed tapping patterns thatshould represent the hot water demand during an actual day instead of a few and largetappings. Even energy efficiency is dealt with in the testing methods by requirements onsystem efficiency for hot water heaters according to the Ecodesign Directive. Demandson hot water have low impact on the heat pump dimensioning, however tapping patternscan be of importance for the heat pump control system design.ivThe operation of three heat pump systems in single family houses is shown throughanalysis of data from field measurements. Two of the systems are equipped with adesuperheater. The analysis shows annual demand, monthly variations of energy use anddetailed heat pump operation during both a summer and winter week.Simplicity and manufacturing costs are prioritized when designing heat pump systemsand performance of hot water heating has not been prioritized in existing systemsolutions. System design can and has been affected by testing methods when connected toa performance requirement. Requirements in the national building code such as limitedmaximum power for space heating have been important. Potential for systemimprovements exist with capacity control and better insulation.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Samhällsbyggnadsteknik -- Husbyggnad (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Civil Engineering -- Building Technologies (hsv//eng)

Nyckelord

system solutions

measurements

Heat pump

hot water

Publikations- och innehållstyp

lic (ämneskategori)

vet (ämneskategori)