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<p dir="ltr">Vapor Compression Systems (VCS) are the most common air conditioning technology. However, the VCS process is energy inefficient due to overcooling and reheating. Liquid Desiccant air conditioning (LDAC) is a potentially more energy-efficient air conditioning technology. LDAC removes vapor in the air using the liquid desiccant’s high-water affinity and controls temperature using an additional cooling device. Additionally, LDAC typically requires heating to regenerate the diluted Liquid Desiccant (LD) for repeated use after absorbing moisture.</p><p dir="ltr">Earlier types of the LDAC systems operated at a relative high concentration and temperature during the dehumidification process, resulting in an increased heat source temperatures required for regeneration, which substantially diminished the energy efficiency advantages of LDAC systems. In the past two decades, researchers have explored a new LDAC system configuration that integrates an LDAC system with a heat pump (HP). The HP can deliver sensible cooling to lower the LD operating temperature and cool the process air. Simultaneously, it provides heating at the condenser side to facilitate the regeneration process. Subsequently, membrane-based dehumidifiers were introduced to separate the LD and airflow using a membrane that permits the passage of water vapor. This approach prevents direct contact, which otherwise would result in LD droplet carryover, addressing concerns related to health and the corrosion of air ducts. An internally cooled membrane-based dehumidifier with enhanced performance garners significant attention, as it essentially functions as a three-stream heat exchanger that facilitates both heat and mass transfer processes. Because of the intricate characteristics of the three-stream heat and mass exchanger, the finite difference models used to analyze the internally cooled membrane dehumidifier is highly detailed and comprehensive. These models are well-suited for assisting in the device’s design but are not suitable for system-level simulations. The lack of simple models for internally cooled membrane-based dehumidifiers limits the evaluation of energy performance at the system level. The limitation becomes particularly pronounced when a HP is integrated, as the model hinders our comprehension of the interactions between the HP and LDAC under the transient operating conditions.</p><p dir="ltr">The thesis research aims to bridge the gaps related to system configuration design, limitations of existing dehumidifier models, and the analysis and assessment of transient system level performance. A model of the internally cooled membrane-based dehumidifier, based on artificial neural networks, was created using data generated through the utilization of a published and detailed finite element dehumidifier model. The resulting model was validated by testing it with out-of-sample data and comparing its results with the validated finite difference model. An LDAC system setup using the internally cooled dehumidifier was established in Modelica using the artificial neural network model created. Furthermore, models of a VCS and an LDAC based on adiabatic dehumidifier were also developed to facilitate performance comparison. The different systems underwent simulation for an entire cooling season spanning from May to September. The internally cooled dehumidifier-based system exhibited superior energy performance, achieving seasonal energy performance levels up to 104% and 34% higher than the VCS and adiabatic dehumidifier systems, respectively. The improved performance in comparison to the VCS is due to the higher temperature operation of the HP. The improvement in comparison to the adiabatic dehumidifier system is due to the improved capacity of the internally cooled dehumidifier to deal with the absorption heat released during dehumidification. Depending on the geographical location, the internally cooled dehumidifier system displayed enhanced performance in the applications characterized by moderate sensible cooling, while its efficiency was relatively lower in arid and hot regions. Additionally, the results demonstrated that the adiabatic system performed similarly to the internally cooled dehumidifier system in locations with high sensible and latent cooling loads.</p><p dir="ltr">This work introduces a pioneering data-driven model for internally cooled membrane liquid desiccant dehumidifiers, representing a significant advancement in the field. The model's computational efficiency and accuracy address the challenges posed by sophisticated and computationally expensive physical models, providing a valuable tool for simulating such devices. The creation of the simple ANN-based dehumidifier model opens the possibility for simulation of internally cooled devices as part of dehumidification systems, whereas as of today its study has been mostly limited to single devices simulations. In the study, a model-based comparison of system performance between an HP-coupled internally cooled dehumidifier-liquid desiccant air conditioning system and HP-coupled adiabatic LDAC, as well as Vapor Compression Systems, elucidates the optimal operational configuration and rationale. Furthermore, a climate sensitivity analysis of system simulations guides researchers toward focusing on the development of HP-coupled internally cooled/heated liquid desiccant systems, particularly in climates that offer the greatest potential for energy savings compared to commonly used vapor compression systems. This comprehensive exploration enhances our understanding and paves the way for more efficient and effective developments in liquid desiccant-based dehumidification technologies.</p>

I Sverige står bostadssektorn för mer än en tredjedel av landets energianvändning. Byggnader måste minska sin energianvändning för att således kunna uppfylla framtida lagkrav om maximal tillåten energianvändning, men också för att minska påverkan till global uppvärmning. Ytterligare en problematik som råder, däribland i Sverige, är bostadsbrist. Kommunala bostadsbolag står inför utmaningen att kunna bygga bostäder snabbt, billigt och miljövänligt för att minska bostadsbristen i landet. Ett sätt att studera två av tre hållbarhetsaspekter vid val av framtida bostadsbyggande är att utföra en livscykelanalys (LCA) och livscykelkostnadsanalys (LCC) kring de tilltänkta husen. LCA:er indikerar vilken miljöpåverkan en produkt förorsakar under dess livslängd. LCC:er avser att studera vilka kostnader produkter ger upphov till under en given analysperiod. Det svenska kommunala bostadsbolaget Stångåstaden AB står inför utmaningen kring bostadsbrist och vill bygga hållbara bostäder. Bostadsbolaget har önskat en jämförande LCA och LCC av två verkliga flerbostadshus som de genom ramavtal kan upphandla, detta är utgångspunkten för denna studie. Den ena byggnaden har stomme av betong, den andra har stomme av trä. Husen är tänkta att placeras i utkanten av Linköping, Sverige. Studien har valt att analysera miljöpåverkan från husens olika livscykelfaser samt kostnader över analysperioden 50 år. Utöver detta studeras även vilka energieffektiviseringsåtgärder (EEÅ) till byggnaderna som är optimala att genomföra för att öka den termiska prestandan hos huskonstruktionerna. Från litteraturen finns det relativt få studier som kombinerar både LCA och LCC för vanligt förekommande hustyper i städer. I dess standardfall påvisade resultatet från LCA:n att huset med betongkonstruktion hade något lägre påverkan i sex av sju studerade miljöpåverkanskategorier, jämfört med flerbostadshuset i trä. Resultatet skilde sig lite åt då annan typ av indata användes. Vad gäller kostnader under husens livslängd var huset i trä ungefär 20 % dyrare jämfört med huset med betongkonstruktion. Trots annan typ av indata var träkonstruktionen dyrare än betongkonstruktionen. Med en kalkylränta på 7,5 % var det inte lönsamt att genomföra EEÅ för husen, med halverad kalkylränta blev det dock lönsamt att tilläggsisolera krypgrunden i huset med trästomme. Fler studier behöver utföras för att generalla slutsatser ska kunna dras kring vilket konstruktionsmaterial som är mest hållbart. Denna studie baseras på två specifika fall. Samma resultat kan eventuellt inte förväntas för andra byggnader med stomme i betong och trä. / The residential sector accounts for more than a third of the energy use in Sweden. To reduce the energy use of buildings is a necessity in order to meet future regulationof maximum allowable energy, but also important to reduce the impact on global warming. Another complexity arising in Sweden is the shortage of accommodation. Municipal housing corporations face the challenge of constructing residences fast, cheap and with concern of environmental effects in order to reduce the shortage of accommodation. One way of assessing two of the three aspects of sustainability when looking at future construction of residential buildings is to carry out a Life Cycle Assessment (LCA) and a Life Cycle Cost Assessment (LCCA). An LCA can indicate what kind of environmental impact a product causes over its lifetime and the LCC allows for assessing what types of costs are associated with the product. For the municipal housing corporation Stångåstaden AB the shortage of accommodation is a reality and their mindset is sustainable construction of residences. This study was conducted upon request from Stångåstaden who wanted a comparative LCA and LCCA between two prefabricated multi-residential buildings that are available to them through a framework agreement. The first building has a concrete foundation and the second one is made of wood. The houses are planned to be placed at the outskirts of Linköping, Sweden. The focus of this study has been to comparatively assess the environmental impact from the different life cycle phases and the economic costs of the two buildings during a time period of 50 years. Moreover, the thesis also analyze the optimal retrofit strategy for the buildings in order to find the optimal (lowest) life cycle cost. Furthermore, the current literature has conveyed relatively few studies that combine both LCA and LCC methodology for house types that are common in most towns. The result from the LCA indicated that the house with concrete construction had a little less impact in six of the seven studied environmental impact categories compared to the house made of wood. The result differed slightly when the input data were changed. Regarding the LCCA the house made of wood was roughly 20 % more expensive than its concrete counterpart. Changing the input data revealed no difference in the result. With an interest rate of 7,5 % no retrofits were profitable for either building, however reducing the interest rate to half its original value made it cost optimal to increase the floor insulation for the house made of wood. More studies should be conducted to be able to draw general conclusions regarding which construction material that is the most sustainable. This thesis is based on two specific and real cases. The same result could possibly not be expected from other studies comparing buildings with concrete and wood construction.