Ahmet Çağlar

University campuses represent large‐scale building environments with substantial heating energy demand and associated carbon emissions, commonly met by natural gas‐fired hot water boilers. This study evaluates the energy and environmental performance of an air‐source gas engine‐driven heat pump (GEHP) as an alternative to a conventional natural gas‐fired hot water boiler (NGHB) for campus‐scale heating. A thermodynamic model was developed for an R410A‐based heat pump driven by a natural gas engine, with waste heat recovery from the engine jacket cooling water and exhaust gases. The effects of evaporation temperature (−30 to 10°C), outdoor temperature (−15 to 10°C), and condenser temperature (40 and 50°C) were investigated in terms of primary energy ratio (PER), ambient heat utilization, natural gas consumption, and CO ₂ emissions. The GEHP achieved PER values of approximately 1.7–3.6 over the investigated evaporation temperature range, substantially exceeding the NGHB reference value of 0.90. As the outdoor temperature increased, the PER increased from 1.85 to 2.80 at a condenser temperature of 40°C and from 1.65 to 2.30 at 50°C. Compared with the NGHB, the GEHP reduced natural gas consumption by approximately 51%–68% at 40°C and 45%–61% at 50°C, while the corresponding CO ₂ emission reductions reached approximately 64% and 53%, respectively. These findings demonstrate that combining ambient heat utilization with engine waste heat recovery can substantially improve primary energy utilization and reduce the carbon footprint of campus‐scale heating, particularly in low‐temperature heating applications.

Operating room air conditioning systems supplying 100% outdoor air generate high energy loads, particularly in hot and humid climates like Antalya. This study evaluates a minimal‐intervention retrofit to improve the energy efficiency of an operating room HVAC system through year‐round recovery of residual exhaust‐air energy downstream of the existing run‐around coil (RAC). Using EnergyPlus 24.1.0, an 8760‐h single‐zone simulation with TMY3 weather data for Antalya compared the reference system with a scenario integrating an auxiliary exhaust‐air‐source air‐to‐water heat pump under identical geometry, ventilation, and operating schedules. This heat pump utilizes exhaust air, after the existing run‐around coil, to provide hydronic pre‐heating or pre‐cooling to the fresh air line without direct refrigerant contact. The annual simulations predicted a 24.75% reduction in total site energy consumption, dropping from 149.66 GJ/year in the reference scenario to 112.62 GJ/year. Specifically, electricity usage decreased from 121.23 to 96.69 GJ/year, and natural gas from 28.43 to 15.93 GJ/year. Heating‐ and cooling‐related energy use decreased by 27.11% and 66.85%, respectively. Consequently, the annual carbon footprint was reduced by 3.90 tCO ₂ e/year (from 17.39 to 13.49 tCO ₂ e/year), corresponding to a 22.42% reduction. The results indicate that the proposed configuration can achieve substantial reductions in annual energy consumption and operational carbon emissions while maintaining complete separation between the supply and exhaust air streams, supporting its application as a minimal‐intervention retrofit option for existing operating‐room HVAC systems.

Fixed-tilt photovoltaic (PV) systems suffer from cosine losses, especially at low solar angles during morning and evening, because they cannot track the Sun’s daily and seasonal motion. This leads to optical misalignment and reduced efficiency in mid-latitude regions such as Türkiye. Although single-axis tracking systems address this issue, field-validated data on their year-long performance under real industrial conditions remain limited. This study presents a 1-year experimental comparison between fixed-tilt and single-axis tracking PV systems operating in Kocaeli, Türkiye (40°49′20.61″ N, 29°55′23.98″ E). Two identical 2.7 kWp grid-tied arrays were monitored at 5-min intervals from September 2024 to August 2025. The single-axis tracker employed an astronomical, time-based control algorithm to maintain favorable panel orientation throughout the day. The results show an annual energy gain of 28.7%, with monthly improvements reaching 38% during the summer. Winter performance was more site- and condition-dependent: under typical snow-free conditions, the realized gain was lower than in summer and strongly influenced by the direct-to-diffuse irradiance balance. In addition, a snow-shedding event highlighted an operational advantage of the tracker under specific winter conditions, but this event should not be interpreted as a universally representative winter-gain benchmark. From an economic perspective, the tracking system achieved a 12.2% lower Levelized Cost of Energy ($ 0.036/kWh) and a shorter payback period (2.25 years) than that of the fixed-tilt system (2.65 years). Therefore, these findings demonstrate the practical benefit of single-axis tracking under the current industrial rooftop conditions; however, the magnitude of the benefit depends on local climate, inverter sizing, snow behavior, and installation alignment.

Hava gibi yoğuşmayan gazlar negatif manometre basınçlarında çalışan adsorpsiyon sistemlerine sızarak performanslarını önemli ölçüde etkileyebilir. Bu çalışma, havanın silika jel-su ve Zeolit 13X-su çiftlerinin adsorpsiyon ve desorpsiyon davranışları üzerindeki etkisini incelemektedir. Kontrollü miktarlarda hava, bir adsorban yatağı ve bir evaporatör/kondenserden oluşan deney düzeneğine enjekte edilerek farklı sıcaklıklarda deneyler gerçekleştirilmiştir. Adsorpsiyon ve desorpsiyon prosesleri, evaporatör/kondenser koşulları sabit tutulurken adsorban sıcaklığının değiştirilmesiyle başlatılmıştır. Havanın etkileri, adsorpsiyon ve desorpsiyon kapasitelerindeki değişimler, basınç dalgalanmaları, gaz ve adsorban sıcaklıkları ile adsorpsiyon/desorpsiyon histerezisi temelinde değerlendirilmiştir. Sonuçlar, artan hava miktarıyla birlikte adsorpsiyon ve desorpsiyon kapasitelerinde önemli düşüşler meydana geldiğini, desorpsiyon proseslerinin adsorpsiyondan daha fazla etkilendiğini göstermektedir. Adsorpsiyon kapasitesindeki azalma, silika jel için üstel, Zeolit 13X için parabolik bir eğilim sergilemiştir. Daha yüksek evaporatör/kondenser sıcaklıkları performans kayıplarını azaltırken, desorpsiyon-adsorpsiyon sıcaklık farkı daha küçük olan silika jel adsorbanlı sistem daha olumsuz etkilenmiştir. Bulgular, adsorpsiyon sistemlerinde hava kaçağının önlenmesinin kritik önem taşıdığını vurgulamaktadır. Atmosfer basıncının yalnızca %0,3–0,9'u kadar iz miktarlardaki hava bile sistem verimliliğini önemli ölçüde düşürebilmektedir.

BiCuSeO oxychalcogenides are promising p-type thermoelectric (TE) materials, yet their TE efficiency is limited by an extremely low intrinsic carrier concentration of ∼ 1018 cm−3. In this study, it is demonstrated that systematic Cd doping triggers the onset of TE performance of BiCuSeO. The substitution of Bi3+ with Cd2+ in a series of Bi1−xCdxCuSeO (x = 0, 0.02, 0.04, 0.06, and 0.08) polycrystalline alloys induces a predictable, near-linear increase in carrier concentration, reaching 3.19 × 1020 cm−3 at x = 0.08 with doping efficiency between 0.27 and 0.41 per dopant. The influence was particularly dramatic at the initial doping (x = 0.02), which boosted the carrier concentration to 1.08 × 1020 cm−3 from an extremely low carrier concentration of 2.82 × 1018 of the pristine sample. This substantial increase successfully activated a high effective mass and power factor. The Boltzmann transport calculations confirm that the electrical transport properties are radically optimized in this high carrier concentration regime. Lattice thermal conductivity decreased from 1.47 W/mK at x = 0 to 1.14 W/mK for x = 0.02 at 300 K, with the reduction being more pronounced gradually at higher doping levels. Consequently, the thermoelectric figure of merit zT showed a significant improvement by 70%, reaching 0.29 for x = 0.02 at 650 K. The optimal TE performance was reached for x ≥ 0.04, as zT values of 0.38–0.43 were attained, representing up to 150% enhancement over the pristine sample. This study demonstrated a facile doping strategy to activate the TE performance of compounds often dismissed for their low intrinsic carrier concentration.